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Offlineimachavel
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so in theory in space.......
    #14796071 - 07/20/11 02:03 AM (12 years, 9 months ago)

if I had a space ship that was 5 miles away from a grenade, and this grenade exploded, in theory, it would travel at the same speed for 5 miles and hit my space ship as though it had exploded right next to it.

without air friction, or gravity, objects in motion tend to stay in motion. this is how the voyager got to pluto with a few rocket corrections right? objects in motion tend to stay in motion makes so much more sense in space


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:kingcrankey: I did not say to edit my signature soulidarity! Now forever I will never remember what I said about understanding the secrets of the universe by paying attention to subtleties!

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Re: so in theory in space....... [Re: imachavel]
    #14796462 - 07/20/11 06:06 AM (12 years, 9 months ago)

It seems like you think grenades are projectiles like bullets.


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[quote]Asante said:
You constantly make posts thatr fling middle school insults at people you don't like mixed in with maladjusted psychopathic comments about wanting to beat up the other poster with a crowbar.

You know how shit you are, you just don't give a fuck for precisely that reason.

I disendorse you.[/quote]

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Re: so in theory in space....... [Re: TheFakeSunRa]
    #14796492 - 07/20/11 06:18 AM (12 years, 9 months ago)

It seems like you think grenades are projectiles like bullets.

Grenades are projectile weapons...the blast doesn't kill you, it's the flying shards of metal that do it. Grenades are designed so that the housing will shred into a lot of metal shards.


To the OP: yes, theoretically the grenade pieces will hit you with the same force as if you were right beside the explosion.

However, this is highly unlikely...at 5 miles out from the blast, the ever-expanding wave of shards will drop off to 1 shard per a few miles of space. It is unlikely that you would be in just the right location to be hit.

That being said...it is theoretically possible.


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Once, men turned their thinking over to machines in the hope that this would set them free.
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OfflineSeussA
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Re: so in theory in space....... [Re: trendal]
    #14796530 - 07/20/11 06:38 AM (12 years, 9 months ago)

Ignoring the grenade, and pretending that it is a bullet instead...

The bullet started at rest and accelerates as it leaves the gun barrel.  Assuming there are no other forces acting on the bullet, does it continue to accelerate (going faster and faster), or does it travel at a fixed velocity?

(I know the answer, this is for the OP to think about...)

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Offlineimachavel
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Re: so in theory in space....... [Re: Seuss] * 3
    #14800127 - 07/20/11 08:39 PM (12 years, 9 months ago)

I don't know, I don't see why it would accelerate. objects at rest tend to stay at rest, objects in motion tend to stay in motion. What would cause the bullet to accelerate further?

I actually looked this up one time online, because a bullet is a lot different from a grenade as an example. a grenade explodes and the metal shards don't travel much more then a few feet or meters usually. a bullet being fired can travel over a mile if it's powerful enough. so a grenade was a much better example to show how things in space will move forever. now when I looked it up online, the only things that would stop a bullet is the gravity of earth, the gravity of the moon, or the gravity of the sun or another planet. if these conditions are right, a bullet being fired will travel through space at the same velocity for an infinite amount of time. but it will eventually collide with something else or fall into orbit or a planets gravity.

Now I once looked up if a bullet can be fired in space, and obviously there is no oxygen in space. And the answer is yes, because a bullet is gas propelled, the oxygen is between the blasting pin(cartridge) and the projectile(bullet) so the pin hits the cartridge and the bullet will still explode. However, you probably could not fire more then a few shots. there is no air in space, and most guns are air cooled. even though it might appear when firing one, that the chamber stays hot for a very long time, the air moving through the chamber actually keeps the gun from getting past a certain temperature as it is cooled in mili seconds with the air. in space firing a few shots might cause the gun to melt, especially if you have multiple clips.

but take in mind, in space certain temperatures make earth temperature look mild, in the day time in space the temperature can get past water boiling temp (212 Fahrenheit) and at night I guess can get below 200 Fahrenheit. Would a gun really be able to fire at such a low temperature? I guess above boiling wouldn't be TOO bad. Remember, in a desert there are no clouds keeping the temperature in, so in the day it's really hot and at night really cold. now imagine in space! there is NOTHING to hold in temperature, except the object itself, so between sun light and sun set, the temperature might easily drop from boiling to below 200 in minutes if not seconds. I suppose there is nothing to measure temperature change in space if no objects are present, so only the object itself would be able to tell you how fast that would be. So would an object at boiling temperature take longer then minutes to reach negative temperature? I doubt it, air does indeed keep temperatures from changing too fast, even though it doesn't appear that way. it also cools things too though, so what you'd probably see with a piece of metal is a hot piece of metal red hot, that stays red hot as long as it's kinetic energy is still within the metal. as soon as it disappears however, in minutes or seconds it would probably reach negative temperature.

now even though air cools things, it also has density, and temperatures are harder to change in density. so it's possible the gun would take a little longer to cool but once it did would cool at an extreme rate. Did I say that right? It's so hard to figure out the difference. Ok according to this I'm right in that it would take longer for things to cool down without atmosphere. also here are some really contradicting space facts:

http://www.sailwithbluemoon.com/how-long-can-you-survive-in-space-without-a-space-suit.html/

apparently nasa says you can survive 30 seconds in space if you hyperventilate to get as much oxygen in your blood as possible, then release your breath so your lungs don't explode at the loss of pressure. but then someone else says people have put pets in a vicum chamber which creates an instant vacuum and kills the pet immediately. really crazy shit. apparently the oxygen and c02 in your lungs start to expand and create bubbles which explode your veins, and also your blood boils as it's mostly water which boils in space at a temperature of like 45 degrees. I guess water is a phenomenon that occurs only on planets with gravity. all the pressure keeps it from boiling. if you were born in space water would be as rare as dry ice or liquid nitrogen. in space 99.98 percent of water is ice or gas, there isn't enough pressure to turn it into water.

space is a pretty hostile place. I feel bad for that dog on sputnik, fucking communists send a dog into space knowing it will die to run tests on life. fucking gar-bage.


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:kingcrankey: I did not say to edit my signature soulidarity! Now forever I will never remember what I said about understanding the secrets of the universe by paying attention to subtleties!

:facepalm: I'm never giving you the password again. Jerk

Edited by imachavel (07/20/11 08:58 PM)

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InvisibleDoc_T
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Re: so in theory in space....... [Re: imachavel]
    #14800149 - 07/20/11 08:42 PM (12 years, 9 months ago)

Well researched!

:highfive:


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InvisibleStonehenge
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Re: so in theory in space....... [Re: Doc_T]
    #14812971 - 07/23/11 10:54 AM (12 years, 9 months ago)

The question of the bullet fired in space is not as simple as it seems. The textbook answer may be that after firing it continues at the same velocity. I believe that is incorrect and i intend to show why.

First of all, the acceleration does not fall to zero the instant the bullet leaves the muzzle. It does drop off but a column of hot gases erupt after the bullet and keep pushing it for a while. On earth, the atmosphere quickly cancels this acceleration and produces braking or deceleration. In space, we could expect the acceleration to continue for some ways after it leaves the gun. As long as some of the gas is pushing on it, it has a tiny acceleration. After the propellant gases diffuse to the point that no molecules of it are pushing, then velocity will not increase from that push, possibly a mile or two out

There are other forces at play including the solar wind. This is composed of fast moving charged particles from the sun. The wind will take over accelerating the bullet a tiny bit until it has left the solar system and the wind falls to zero. Even then we still have another force which is light pressure. Light exerts a tiny push on anything it hits. So in theory at least, the bullet could continue to accelerate indefinitely.


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Offlineimachavel
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Re: so in theory in space....... [Re: Stonehenge]
    #14825435 - 07/26/11 12:12 AM (12 years, 9 months ago)

umm, from what I know in space, only gravity of a planet or another planets orbit will change the speed and velocity of the bullet. nothing else will slow it down, it should go on forever. from what I know a comet is a piece of rock from a planet that exploded years ago, that is still traveling at the same exact speed.

why would any of this other stuff be different? whether the bullet would explode is the question


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:kingcrankey: I did not say to edit my signature soulidarity! Now forever I will never remember what I said about understanding the secrets of the universe by paying attention to subtleties!

:facepalm: I'm never giving you the password again. Jerk

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InvisibleDieCommie

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Re: so in theory in space....... [Re: imachavel]
    #14825589 - 07/26/11 12:54 AM (12 years, 9 months ago)

.

Edited by DieCommie (11/16/16 10:04 AM)

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OfflineSeussA
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Re: so in theory in space....... [Re: DieCommie]
    #14826259 - 07/26/11 06:25 AM (12 years, 9 months ago)

> In physics we sometimes call those 'higher order terms'.

Or as my physics adviser used to say, "Assume that we have a spherical chicken traveling with a velocity of ..." along with "Take any complex physics problem and make assumptions until the problem becomes easy to solve."  (The last statement was usually used in the context of theoretical and experimental physics.)


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OfflineSeussA
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Re: so in theory in space....... [Re: Stonehenge]
    #14826274 - 07/26/11 06:34 AM (12 years, 9 months ago)

> After the propellant gases diffuse to the point that no molecules of it are pushing, then velocity will not increase from that push, possibly a mile or two out

Without the walls of the barrel, the gasses and the bullet are going to quickly reach equilibrium.  Remember, the mass of the bullet is many orders of magnitude larger than the the mass of the gas. Acceleration (ignoring gravity, solar wind, etc) will drop to nearly zero almost instantaneously (around 1E-3 second) after the combustion gasses are no longer constrained by the barrel.


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InvisibleStonehenge
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Re: so in theory in space....... [Re: Seuss]
    #14827831 - 07/26/11 02:39 PM (12 years, 9 months ago)

Diecommie, you are correct. I was deliberately ignoring many factors, chief among them gravity which would also act on the bullet. Gravity could hinder, modify or increase the speed of the bullet. The voyager spacecraft used the slingshot effect of a large planet's gravity, in this case jupiter, to give it added speed so it could escape the solar system without using a lot of fuel. There are also electrostatic fields and static em fields in space which could act on a bullet.

>Without the walls of the barrel, the gasses and the bullet are going to quickly reach equilibrium.  Remember, the mass of the bullet is many orders of magnitude larger than the the mass of the gas. Acceleration (ignoring gravity, solar wind, etc) will drop to nearly zero almost instantaneously (around 1E-3 second) after the combustion gasses are no longer constrained by the barrel.

It will drop off quickly but not instantaneously. I estimated a mile or two before it reached zero. Don't forget that the gas has a higher velocity than the bullet, has a forward motion and is produced for an instant after the bullet exits. That explains the flash from a muzzle seen at night and why flash suppressant guards must be used on combat. The propellant keeps burning long enough that we can see it burn after it exits the barrel behind the bullet. What e are you referring to and by -3 do you mean minus 3 or to the  -3 power? That would be shown as e^-3. But you know that so we can only guess at your meaning and how you arrived at it. If you mean e as in the mathmatical e, how does that relate to time in this case?

Exactitude will never be had but i wanted to show that it was not a simple situation. The gravity of the gun itself would pull on the bullet so it's a highly complex problem if you want to get it to perfection. Can't be done.

As for the gun overheating, that will not be a problem. In space, materials give off heat and cool rapidly unless they are close to a source of radiant heat.


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“A democracy cannot exist as a permanent form of government. It can only exist until the voters discover that they can vote themselves largesse from the public treasury. From that moment on, the majority always votes for the candidates promising the most benefits from the public treasury with the result that a democracy always collapses over loose fiscal policy, always followed by a dictatorship.” (attributed to Alexis de Tocqueville political philosopher Circa 1835)

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InvisibleDieCommie

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Re: so in theory in space....... [Re: Stonehenge]
    #14827979 - 07/26/11 03:08 PM (12 years, 9 months ago)

10e-3 = 1x10-3, he means a millisecond.


Quote:

In space, materials give off heat and cool rapidly unless they are close to a source of radiant heat.




Well, a vacuum is a great insulator.  I dont think it would cool rapidly.  There will be no conduction and no convection, only radiation.

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Re: so in theory in space....... [Re: DieCommie]
    #14828130 - 07/26/11 03:40 PM (12 years, 9 months ago)

>Well, a vacuum is a great insulator.  I dont think it would cool rapidly.  There will be no conduction and no convection, only radiation.

Bingo! radiation it is. Even highly polished objects lose heat rapidly in space. Deep space has the temperature equivalent of nearly zero. That is to say, thermal radiation coming in is equal to that. Roughly.

>10e-3 = 1x10-3, he means a millisecond.

That isn't what he said, he said 1e-3. I'm not that up on math so i don't know all the shorthand terms. I recall from my days in college that e was about 2.7 but if he meant log to the base e it would be something else. So i'm still in the dark. Engineers are used to talking in highly cryptic terms that will throw the layman. They love doing that.


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“A democracy cannot exist as a permanent form of government. It can only exist until the voters discover that they can vote themselves largesse from the public treasury. From that moment on, the majority always votes for the candidates promising the most benefits from the public treasury with the result that a democracy always collapses over loose fiscal policy, always followed by a dictatorship.” (attributed to Alexis de Tocqueville political philosopher Circa 1835)

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InvisibleDieCommie

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Re: so in theory in space....... [Re: Stonehenge]
    #14828259 - 07/26/11 04:02 PM (12 years, 9 months ago)

Right, I wrote that wrong.  1e-3 = 1x10-3.  the 'e', often written as 'EE' or 'ee' is the calculator button for ' x 10 ^ '.

As for the temperature... I believe the amount of heat radiating away or on to it is really low compared to the heat that can be lost through convection.  The gun would thus stay hot longer in space, unless you fired it near a star to keep it hot.

Edited by DieCommie (07/26/11 04:12 PM)

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Re: so in theory in space....... [Re: DieCommie]
    #14828390 - 07/26/11 04:27 PM (12 years, 9 months ago)

>Right, I wrote that wrong.  1e-3 = 1x10-3.  the 'e', often written as 'EE' or 'ee' is the calculator button for ' x 10 ^ '.

Not on my calculator. But a millisecond would not be correct either. The gas rushing out would continue at least a second though it would drop off rapidly. We are talking theory here, not practicality.

>As for the temperature... I believe the amount of heat radiating away or on to it is really low compared to the heat that can be lost through convection.  The gun would thus stay hot longer in space, unless you fired it near a star to keep it hot.

The suns radiated heat travels an average of 93 million miles and you can feel it easily. Would you say radiation doesn't work very well? The earth would be cold without it. Objects in space quickly cool to near zero temps unless they are warmed in some way. The space shuttles and crafts had to equalize the heat taken in by the sun and radiated away. The side away from the sun got extremely cold and the other side got very hot unless something was done.

But if it was near enough to the sun, then it would stay hot or heat up even more.


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“A democracy cannot exist as a permanent form of government. It can only exist until the voters discover that they can vote themselves largesse from the public treasury. From that moment on, the majority always votes for the candidates promising the most benefits from the public treasury with the result that a democracy always collapses over loose fiscal policy, always followed by a dictatorship.” (attributed to Alexis de Tocqueville political philosopher Circa 1835)

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InvisibleDieCommie

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Re: so in theory in space....... [Re: Stonehenge]
    #14828401 - 07/26/11 04:29 PM (12 years, 9 months ago)

Quote:

Objects in space quickly cool to near zero temps unless they are warmed in some way.




If by quickly you mean as slow as possible, then yes.  :tongue:  Again, vacuum is the best insulator there is.

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Re: so in theory in space....... [Re: DieCommie]
    #14828427 - 07/26/11 04:34 PM (12 years, 9 months ago)

Firing a gun several times rapidly would melt it, yes.
No way to radiate the heat in a vacuum until it gets glowing hot and starts emitting photons.

Even in atmosphere you can do it, howitzers have strict limits on firing rates for this reason.
(One I worked on was "4 rounds per minute for first three minutes, then one round a minute after that.")


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Re: so in theory in space....... [Re: Doc_T]
    #14828764 - 07/26/11 05:33 PM (12 years, 9 months ago)

Doc t, i'm sure you are correct about howitzers. Heat loss in a vacuum would depend on the surface of object. Bright shiny metal would radiate the least, and black will radiate the most.

Objects are radiating photons of energy at all times. When you are next to an object at the same general temperature as yourself, you feel no heat but it is radiating heat. Have you ever been right next to something very cold and felt like it was radiating cold? Cold can not be radiated, only heat, light and so on. When your hand is next to an object of about the same temp, it radiates heat to you at the same rate you radiate it to the object. If the object is very cold, it radiates less heat. You are giving it heat and getting very little in return. It feels like the object radiates cold.


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“A democracy cannot exist as a permanent form of government. It can only exist until the voters discover that they can vote themselves largesse from the public treasury. From that moment on, the majority always votes for the candidates promising the most benefits from the public treasury with the result that a democracy always collapses over loose fiscal policy, always followed by a dictatorship.” (attributed to Alexis de Tocqueville political philosopher Circa 1835)

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InvisibleDieCommie

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Re: so in theory in space....... [Re: Stonehenge]
    #14828785 - 07/26/11 05:36 PM (12 years, 9 months ago)

The amount of heat lost from an object depends on its temperature alone (blackbody radiation).  The qualities you describe, the surface and the shine, only affect how incoming radiation will interact with the object.

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Re: so in theory in space....... [Re: DieCommie]
    #14828837 - 07/26/11 05:46 PM (12 years, 9 months ago)

Quote:

DieCommie said:
The amount of heat lost from an object depends on its temperature alone (blackbody radiation).




Is that per unit of area?
Say you have a pound of feathers and a pound of lead, but instead of dropping them you measure the temp.
Feathers have vast surface area... do they cool off faster in a vacuum than some lead shot of equal mass and starting temp?
(Part of me wants to argue each side of this.)


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InvisibleDieCommie

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Re: so in theory in space....... [Re: Doc_T]
    #14828870 - 07/26/11 05:51 PM (12 years, 9 months ago)

Yea, per unit surface area.  Thats right.

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Re: so in theory in space....... [Re: DieCommie]
    #14828946 - 07/26/11 06:03 PM (12 years, 9 months ago)

:header:





Space is weird, physics is weird.


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InvisibleDieCommie

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Re: so in theory in space....... [Re: Doc_T]
    #14829090 - 07/26/11 06:27 PM (12 years, 9 months ago)

Another weird thing I thought of in this thread is that the bullet will torque around and spin longways.  Even though its fired out of barrel spinning around its low moment of inertia axis, as it radiates away energy (from blackbody and the non-rigid nature of the bullet) it will re-align itself such that it spins long ways over itself.  This is the bullet conserving its angular momentum while having a lower angular velocity from dissipated energy.

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Re: so in theory in space....... [Re: DieCommie]
    #14829285 - 07/26/11 07:00 PM (12 years, 9 months ago)

You are spouting gibberish now, dc. You were perfectly lucid a while ago. What force would cause the bullet to do what you say?

It's true that the higher the temp the greater the amount of energy radiated. However, white and bright shiny surfaces give off and receive the least amount of heat. Black gives off and absorbs the most. Why do you think they call it "blackbody" radiation?


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“A democracy cannot exist as a permanent form of government. It can only exist until the voters discover that they can vote themselves largesse from the public treasury. From that moment on, the majority always votes for the candidates promising the most benefits from the public treasury with the result that a democracy always collapses over loose fiscal policy, always followed by a dictatorship.” (attributed to Alexis de Tocqueville political philosopher Circa 1835)

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InvisibleDieCommie

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Re: so in theory in space....... [Re: Stonehenge]
    #14829387 - 07/26/11 07:21 PM (12 years, 9 months ago)

Quote:

What force would cause the bullet to do what you say?




The torque due to the non-rigid nature of the bullet.  A spinning object will always torque it self into its principle axis due to the combination of conservation of angular momentum and conservation of energy.

Quote:

Why do you think they call it "blackbody" radiation?




Because you ignore any radiation directed on to the object and consider only radiation emitted from the object.  Blackbody radiation (per unit area) is a function of temperature alone.  Room temperature coloring is irrelevant because it comes from radiation that is reflected off of the object, not emitted from it.  The color of a blackbody is also uniquely determined by the temperature(not the other way around):smile:.

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Re: so in theory in space....... [Re: Stonehenge] * 1
    #14829719 - 07/26/11 08:23 PM (12 years, 9 months ago)

Quote:

Stonehenge said:
You are spouting gibberish now, dc. You were perfectly lucid a while ago. What force would cause the bullet to do what you say?




I'm not sure it matters, though I believe diecommie mentioned electromagnetic radiation, which would amount to a force against the bullet opposite to the direction it was emitted.

This result seems nonintuitive to me, as well, but looking at the equations, it seems he'd be correct.  As angular momentum is angular velocity times moment of inertia but rotational kinetic energy is angular momentum times the square of the angular velocity, and the angular momentum would be conserved, the case with the lower angular velocity and higher moment of inertia would have a lower kinetic energy, being more favorable than the higher energy state. 

As the bullet will be subject to any number of forces, including the radiative cooling, its energy will decrease and the tumbling state will be more energetically favorable.

If you look at a simple ratio of KE(rot)/KE(tum)=I(tum)w(tum)w(tum)/[I(rot)w(rot)w(rot)], you can see that since the momentum is conserved, I(tum)w(tum)=I(rot)w(rot)=L(tum)=L(rot)

hence, KE(rot)/KE(tum)=L/L*w(rot)/w(tum), thus KE(rot)/KE(tum)=w(rot)/w(tum).  Since by definition the rotating bullet has a smaller moment and hence greater angular velocity, this ratio is greater than one and the tumbling bullet thus has lower kinetic energy than the rotating bullet of the same angular momentum

(been a while since I've done this kinda thing, hope that's correct, lol)

Quote:

It's true that the higher the temp the greater the amount of energy radiated. However, white and bright shiny surfaces give off and receive the least amount of heat. Black gives off and absorbs the most. Why do you think they call it "blackbody" radiation?




I think its called black body radiation because the interest is on the radiation emitted by the particular object due to its thermal energy, rather than due to reflected radiation.  As a perfect black body will not reflect energy, it is the object relevant to this case.

You haven't proven that an object's color effects the energy it radiates, all else being equal, you've simply declared it to be so.  As far as I can tell, the only difference would be that a non-black object would reflect some radiation and hence you could spuriously presume the detected radiation is from the object's thermal energy when it is not.

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Re: so in theory in space....... [Re: johnm214]
    #14829739 - 07/26/11 08:26 PM (12 years, 9 months ago)

Color aside, does it matter at all what the material is?
Metal, wood, plastic, ionic salt, diamond, etc?


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Re: so in theory in space....... [Re: Doc_T]
    #14829749 - 07/26/11 08:29 PM (12 years, 9 months ago)

Isn't pluto like 200 lightyears away or something? How did we get something there?


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Re: so in theory in space....... [Re: Doc_T] * 1
    #14829793 - 07/26/11 08:35 PM (12 years, 9 months ago)

Quote:

Doc_T said:
Color aside, does it matter at all what the material is?
Metal, wood, plastic, ionic salt, diamond, etc?





No, that's the point of the matter: to investigate the radiation due to the thermal energy of the object and nothing else.

Of course since real objects like those you mention don't have perfect black bodies and have an internal structure that absorbs some wavelengths preferentially and reemits still other wavelengths, they don't have this perfect spectrum even if you ignore relections, but the material will still approximate the behavior of a black body to some degree, which is why its a useful concept: its the ideal case that neglects the potentially unknown intervening factors.

The color of real objects also is a function of those frequencies of light they simply reflect to some degree without absorbing, so a simple measure of the radiation coming from a 'real object' with imperfect absorption will neccesarily not be recording just the radiation attributed to the thermal energy of the object.

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Re: so in theory in space....... [Re: johnm214]
    #14830147 - 07/26/11 09:45 PM (12 years, 9 months ago)

.

Edited by DieCommie (11/16/16 10:30 PM)

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Re: so in theory in space....... [Re: DieCommie]
    #14830563 - 07/26/11 11:04 PM (12 years, 9 months ago)

Quote:

DieCommie said:
  For a bullet, the higher moment of inertia is about the axis where the bullet rotates as a throwing knife.  Normally, a high spin and the resistance of the air renders the nature irrelevant and the bullet stays spinning along its low inertia axis for the duration of its flight.





right, but the reason why this is the preferred rotation (tubmling) is because its a lower energy state for the same angular momentum, correct? 

That's one of the things I really like about the natural sciences: even in dispartate fields a few fundamental bits of information drive most of the processes, such as a lower energy state being more stable than a high energy state.  From that you get chemical reactions or bullets tumbling instead of rotating, osmotic pressure, and any number of other things: all going from a high energy state to a low energy state.

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Re: so in theory in space....... [Re: johnm214]
    #14830726 - 07/26/11 11:35 PM (12 years, 9 months ago)

Quote:

the reason why this is the preferred rotation (tubmling) is because its a lower energy state for the same angular momentum, correct? 




Yea, that's the way I see it.

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Re: so in theory in space....... [Re: Seuss]
    #14831289 - 07/27/11 03:12 AM (12 years, 9 months ago)

Quote:

Seuss said:
> After the propellant gases diffuse to the point that no molecules of it are pushing, then velocity will not increase from that push, possibly a mile or two out

Without the walls of the barrel, the gasses and the bullet are going to quickly reach equilibrium.  Remember, the mass of the bullet is many orders of magnitude larger than the the mass of the gas. Acceleration (ignoring gravity, solar wind, etc) will drop to nearly zero almost instantaneously (around 1E-3 second) after the combustion gasses are no longer constrained by the barrel.




yes that's true, also air pressure might build up in the barrel after the projectile is fired, along with the gaseous chemical reaction from the cartridge exploding, that helps the bullet pop out of the barrel faster. although this is contradictory, because of the fact that the air pressure should slow the bullet down as it tries to pop out of the barrel. so maybe one way or another it would be faster or slower, but the reaction is so simple, that I honestly believe the speed would hardly change much. I think it would either work at just about normal speed or it wouldn't work at all. It would be very interesting for a scientist/astronaut out in space to try this, but how would you measure the bullets speed? LOL. I'm guessing the experiment would mostly be just to see if the pistol fired or not :shrug:


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Re: so in theory in space....... [Re: imachavel]
    #14831310 - 07/27/11 03:18 AM (12 years, 9 months ago)

Of course it would fire. Gunpowder is self-oxidizing.
Measure the speed with radar or a camera, like Mythbusters.


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Re: so in theory in space....... [Re: DieCommie]
    #14831323 - 07/27/11 03:24 AM (12 years, 9 months ago)

Quote:

DieCommie said:
Right, I wrote that wrong.  1e-3 = 1x10-3.  the 'e', often written as 'EE' or 'ee' is the calculator button for ' x 10 ^ '.

As for the temperature... I believe the amount of heat radiating away or on to it is really low compared to the heat that can be lost through convection.  The gun would thus stay hot longer in space, unless you fired it near a star to keep it hot.




I believe it takes longer for things to cool down actually. remember, cold isn't an actual temperature, it's simply the absence of heat. here on earth, something really cold cools down heat instantly, because of all the molecules coldness around it, that are moving slower, they absord the kinetic radiation. in space there is no cold, only a lack of radiation except provided by the sun, therefore things will not regain heat until the sun hits them. so it will cool down and stay cold longer. but the cooling process won't be quick. on earth, "cold" air or "cold" water has an effect on things with kinetic radiation. because they absorb the radiation of the "hot" element. but there is really no true cold, only the slowing down of molecular movement. obviously in space, there is no molecular movement, as there is no atmosphere, outside of the element, so whatever kinetic radiation energy pours out of it, or dies down in the object, won't be regained. but also without atmosphere there will be no other molecules to absorb the kinetic radiation, so it will take longer to cool down.

then again, atmosphere, even below zero, has kinetic radiation, that will keep an object from cooling down completely, as it absords kinetic radiation from the atmosphere. so in space, things should take longer to cool, but once cool, should really eventually reach a temperature as cold as liquid nitrogen, no matter the object. as there is absolutely no radiation energy in space aside from the suns rays. but keep in mind, there is no such thing as cold, only the lack of radiation energy. how this would effect a bullets velocity is beyond me.


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Re: so in theory in space....... [Re: Doc_T]
    #14831329 - 07/27/11 03:26 AM (12 years, 9 months ago)

Quote:

Doc_T said:
Of course it would fire. Gunpowder is self-oxidizing.
Measure the speed with radar or a camera, like Mythbusters.




that's right I forget, radar waves work through space, as do radio waves, which are different wave lengths of the same waves if I'm correct. do you think the bullet would fire at the same speed though? well it'd be ABOUT the same speed anyway


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Re: so in theory in space....... [Re: imachavel]
    #14831339 - 07/27/11 03:30 AM (12 years, 9 months ago)

Slightly faster muzzle velocity is my guess, since there's no air in the barrel.
Just a tiny difference, probably within normal variance of real bullets.


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Re: so in theory in space....... [Re: johnm214]
    #14831344 - 07/27/11 03:36 AM (12 years, 9 months ago)

Quote:

johnm214 said:
Quote:

Stonehenge said:
You are spouting gibberish now, dc. You were perfectly lucid a while ago. What force would cause the bullet to do what you say?




I'm not sure it matters, though I believe diecommie mentioned electromagnetic radiation, which would amount to a force against the bullet opposite to the direction it was emitted.

This result seems nonintuitive to me, as well, but looking at the equations, it seems he'd be correct.  As angular momentum is angular velocity times moment of inertia but rotational kinetic energy is angular momentum times the square of the angular velocity, and the angular momentum would be conserved, the case with the lower angular velocity and higher moment of inertia would have a lower kinetic energy, being more favorable than the higher energy state. 

As the bullet will be subject to any number of forces, including the radiative cooling, its energy will decrease and the tumbling state will be more energetically favorable.

If you look at a simple ratio of KE(rot)/KE(tum)=I(tum)w(tum)w(tum)/[I(rot)w(rot)w(rot)], you can see that since the momentum is conserved, I(tum)w(tum)=I(rot)w(rot)=L(tum)=L(rot)

hence, KE(rot)/KE(tum)=L/L*w(rot)/w(tum), thus KE(rot)/KE(tum)=w(rot)/w(tum).  Since by definition the rotating bullet has a smaller moment and hence greater angular velocity, this ratio is greater than one and the tumbling bullet thus has lower kinetic energy than the rotating bullet of the same angular momentum

(been a while since I've done this kinda thing, hope that's correct, lol)

Quote:

It's true that the higher the temp the greater the amount of energy radiated. However, white and bright shiny surfaces give off and receive the least amount of heat. Black gives off and absorbs the most. Why do you think they call it "blackbody" radiation?




I think its called black body radiation because the interest is on the radiation emitted by the particular object due to its thermal energy, rather than due to reflected radiation.  As a perfect black body will not reflect energy, it is the object relevant to this case.

You haven't proven that an object's color effects the energy it radiates, all else being equal, you've simply declared it to be so.  As far as I can tell, the only difference would be that a non-black object would reflect some radiation and hence you could spuriously presume the detected radiation is from the object's thermal energy when it is not.




why does all this temperature come into play? where do you get the idea that the temperature effects the bullets speed. a comet is made of ice, freezing fucking cold, floating through space faster then the fastest rocket we have here, without friction from the atmosphere nothing will cause the comets temperature to rise.

a bullets temperature will not effect it's speed, it has already left the barrel of the gun, and as the law of physics go, in space, an object should travel at the same speed continually until infinity, unless some other force act on it to slow it down. right now we are just trying to figure out if the bullet will leave the gun barrel in the first place.


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Re: so in theory in space....... [Re: Doc_T]
    #14831348 - 07/27/11 03:38 AM (12 years, 9 months ago)

Quote:

Doc_T said:
Slightly faster muzzle velocity is my guess, since there's no air in the barrel.
Just a tiny difference, probably within normal variance of real bullets.




yeah I'm guessing. up late huh? me also. so if the bullet was fired outside the milky way galaxy, with no gravity and no planets orbit to effect the bullet, until it reaches another galaxy, assuming it will, it SHOULD travel at the same speed it left the barrel muzzle at until infinity. correct??


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Re: so in theory in space....... [Re: imachavel]
    #14831350 - 07/27/11 03:41 AM (12 years, 9 months ago)

I'm up early. :frown:

There will be gravity in space, and also a certain amount of material, even between galaxies.
But yeah, a bullet would travel for millions of years until it hit something.


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Re: so in theory in space....... [Re: Doc_T]
    #14831389 - 07/27/11 03:58 AM (12 years, 9 months ago)

it should. check this out:



I wish he threw those balls really hard I'd like to see how they bounce around :lol:


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Re: so in theory in space....... [Re: DieCommie]
    #14831411 - 07/27/11 04:18 AM (12 years, 9 months ago)

> 1e-3 = 1x10-3.

Yes, that is what I meant. 

> The gas rushing out would continue at least a second though it would drop off rapidly.

We are talking about acceleration (and equilibrium), not 'continuing'.  I made a rough estimate given the mass of the gas versus the mass of the bullet, the freedom of the gas to diffuse, and an estimated speed of the bullet.  If the bullet has a velocity of 1000m/s, then I don't find it unreasonable that the gasses would continue to add to the bullets acceleration for the first meter after leaving the barrel, or around 1/1000th of a second.  After that, the force that the gas can exert on the bullet is going to be negligible, thus the acceleration is going to be zero (negligible).


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Re: so in theory in space....... [Re: Seuss]
    #14832502 - 07/27/11 11:09 AM (12 years, 9 months ago)

Glad to see you back in the thread, seuss. This has really revived interest in science so no matter what we conclude, it contributed something.

Sorry, but i'm going to have to be picky here and pick apart many of your statements. I realize you were speaking in general so maybe that isn't totally fair but we want to find the truth, not generalities.

>1/1000th of a second.  After that, the force that the gas can exert on the bullet is going to be negligible, thus the acceleration is going to be zero (negligible).

First of all, negligible is not the same as zero. We are talking about whether there will be any change in the bullets velocity, either positive or negative acceleration. There is not threshold below which we can ignore forces and say they are "negligible" A force that exerted one billionth of a gram of force on the bullet would have a major impact on it's trajectory over a long distance. We are talking about space, not firing a bullet into a target a short distance away. Therefore even slight forces must be acknowledged.

The bullets mass is not "many orders of magnitude" greater than that of the gas. The mass of the gas is equal to the mass of the propellant which is perhaps one order of magnitude less than that of the bullet. As long as the hot gas pushed into the bullet, a slight acceleration would result. It would fall to zero when no more molecules of gas hit the bullet.

DieCommie, there is a reason the bullet has an angular momentum put on it by rifling in the barrel. It is precisely to prevent tumbling, not to cause it. This is due to the gyroscopic effect.

http://en.wikipedia.org/wiki/Gyroscope

Far from causing tumbling, spin tends to resist tumbling when traveling through the atmosphere. In space where there is no outside force which could cause tumbling, the spin prevails. The energy in the rotation of any object resists a change in orientation such as spinning end over end. Without a strong outside force, the bullet will continue to spin and to travel with the nose forward.

As for the color affecting the amount of heat absorbed or given off, pretty much anyone knows that dark colors absorb heat much faster than light ones. Try wearing black clothes out in the sun on a hot day if you doubt it. As for dark colors radiating more heat, why do you suppose parkas and other cold weather gear is usually white and never black? Here is an excerpt from a physics professor

http://www.newton.dep.anl.gov/askasci/phy00/phy00156.htm

>The darker the object, the better its emission of heat because it is a better absorber of light.

I hope this settles a few of the points. There are still more things to discuss, ever slighter forces which would act on the bullet. Eventually it would hit atoms or molecules of hydrogen which exist between galaxies.


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Re: so in theory in space....... [Re: Stonehenge]
    #14832769 - 07/27/11 12:13 PM (12 years, 9 months ago)

> First of all, negligible is not the same as zero.

I use the words interchangeably in the context we are discussing.  As an example, there are a few particles of gas (hanging out in space) that the bullet is going to hit as well that are going to slow the bullet down a little bit as energy is transferred from the bullet to these few particles of gas.  However, the net result is negligible... as in literally unmeasurable... thus given the magnitude of the numbers we are working with, the effect is insignificant.

> The bullets mass is not "many orders of magnitude" greater than that of the gas. The mass of the gas is equal to the mass of the propellant which is perhaps one order of magnitude less than that of the bullet.

I'm talking specifically about the mass of the few stray gas particles that are going to strike the bullet some time after the bullet has left the barrel.  Once free from the confines of the barrel, most of the gas is going to quickly dissipate.  Even in the barrel, you might have 30 grains of propellant vs 150 grains of bullet.  That is still over an order of magnitude difference.

A good thought experiment... pretend that the gas is a single solid object behind the bullet (such as another bullet) and imagine what happens when that single large object pushes the bullet out of the barrel.  If the single large object continues to accelerate the bullet, what force is acting on the single large object?


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Re: so in theory in space....... [Re: Seuss]
    #14833139 - 07/27/11 01:18 PM (12 years, 9 months ago)

OK, you clarified what you meant by several things. If you are referring to the time at which the gas has diffused down to a few molecules, it's not too out of line to call it negligible. However, over a long distance even the solar wind will make a difference.

I also mentioned the stray atoms of gas the bullet would encounter. It's my understanding that the density of the galactic nebulae is about 1 atom of hydrogen per cubic meter of space. About what we would call an extremely hard vacuum. Empty space would be expected to have a much lower density.

>Once free from the confines of the barrel, most of the gas is going to quickly dissipate.

Sure, but it will follow a cone shape as it's tendency to spread out interacts with it's forward velocity. .001 seconds later i don't think we will be down to a molecule or two.

>Even in the barrel, you might have 30 grains of propellant vs 150 grains of bullet.  That is still over an order of magnitude difference.

Correct me if i'm wrong but i thought an order of magnitude was 10x?

>A good thought experiment... pretend that the gas is a single solid object behind the bullet (such as another bullet) and imagine what happens when that single large object pushes the bullet out of the barrel.  If the single large object continues to accelerate the bullet, what force is acting on the single large object?

Then we would have a totally different situation. Rather than the propellant being a solid object that got it's momentum from something else, it is a dynamic expanding gas. It is pushing on the gun at the same rate it pushes on the bullet so the gun is going to accelerate backward after firing. The gas continues to expand and even in empty space, a gas can expand and push in all directions. I grant you it would be quickly dissipated and we can discuss what amount of time it would take to get down to a molecule or two striking the bullet. It's the equivalent of an explosion in space and the force is generated by that explosion.


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Re: so in theory in space....... [Re: Stonehenge]
    #14833201 - 07/27/11 01:30 PM (12 years, 9 months ago)

Quote:

Stonehenge said:


First of all, negligible is not the same as zero. We are talking about whether there will be any change in the bullets velocity, either positive or negative acceleration. There is not threshold below which we can ignore forces and say they are "negligible" A force that exerted one billionth of a gram of force on the bullet would have a major impact on it's trajectory over a long distance. We are talking about space, not firing a bullet into a target a short distance away. Therefore even slight forces must be acknowledged.




You use relative terms such as "major" impact and "long" distance versus "short" distance.  To speak of such relative qualities and then conclude there is no negligible factor, such as a nanogram, is silly.

Quote:



DieCommie, there is a reason the bullet has an angular momentum put on it by rifling in the barrel. It is precisely to prevent tumbling, not to cause it. This is due to the gyroscopic effect.




?  What's your point?  The angular momentum is conserved when the bullet changes from spinning on its long axis to its short axis.  As for the intent of using rifling, unfortunately the universe isn't too concerned with our intentions.


Quote:


Far from causing tumbling, spin tends to resist tumbling when traveling through the atmosphere. In space where there is no outside force which could cause tumbling, the spin prevails.




Spin is not conserved, angular momentum is.  You have not established that there is any violation of the conservation of momentum for a bullet to transition to turning about its short axis, so there is no reasoned objection.  I've worked out above a very simple example showing why the tumbling bullet has less kinetic energy for the same angular momentum, and you've taken no issue with this nor provided any other objection.

As for the relatively slight forces on the bullet compared to earth, you don't say what the relevance of this comparison is, and I don't see it, either.  The discussion is over what the bullet will tend to do over time, what the lower energy state is, and hence I don't see how a discussion of the relative time it would take could be contradictory in the slightest.

Quote:

The energy in the rotation of any object resists a change in orientation such as spinning end over end. Without a strong outside force, the bullet will continue to spin and to travel with the nose forward.




Again, what does the strength of the force have to do with a discussion of the bullet's tendancy over time? 

Quote:

As for the color affecting the amount of heat absorbed or given off, pretty much anyone knows that dark colors absorb heat much faster than light ones.




So what?

Quote:

As for dark colors radiating more heat, why do you suppose parkas and other cold weather gear is usually white and never black? Here is an excerpt from a physics professor




Ignoring style, I would imagine its to reflect radiation.  As the flux through the parka from the body is surely greater than that from the environment, this makes sense.  What does this have to do with black body radiation?  The whole point is to ignore reflection.



Quote:

>The darker the object, the better its emission of heat because it is a better absorber of light.




So what?  The whole point is the emissions due to the object's own thermal energy, temperature.  Considering a case where the object is heated by incoming radiation supposes an additional energy source, which is not what the black body case is examining.

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Re: so in theory in space....... [Re: Seuss]
    #14833213 - 07/27/11 01:32 PM (12 years, 9 months ago)

.

Edited by DieCommie (11/10/16 07:22 PM)

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Re: so in theory in space....... [Re: DieCommie]
    #14833375 - 07/27/11 02:06 PM (12 years, 9 months ago)

DC and john, i'm sorry you don't understand the physics of a gyroscope or how it affects the trajectory of a bullet. I provided a link but it seems to have been ignored. You can say "so what" as many times as you want but not only physicists but people in the field have proven what i said to be true.

>Spin is not conserved, angular momentum is

Spin IS angular momentum. In order for the bullet to tumble end over end, it must overcome not only inertia but also the spin put on by the barrel. You and dc seem to think the angular momentum will translate into end over end tumbling due to your interpretation of something or other. You have shown nothing to demonstrate this phenomenon or given any links. You don't see seuss agreeing with that part. He knows better.

>Yes, anyone knows that dark clothes absorb heat faster.  But they do not give off heat faster.

Did you follow that link? You are saying you know more about the subject than a physics professor? Where is your proof of that? I gave my evidence, where is yours?


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Re: so in theory in space....... [Re: Stonehenge]
    #14833505 - 07/27/11 02:33 PM (12 years, 9 months ago)

Quote:

Stonehenge said:
DC and john, i'm sorry you don't understand the physics of a gyroscope or how it affects the trajectory of a bullet. I provided a link but it seems to have been ignored. You can say "so what" as many times as you want but not only physicists but people in the field have proven what i said to be true.




You don't seem to understand that a bullet is not a gyroscope.

Quote:


Spin IS angular momentum.




"Spin", as you are using it, is a loose, ambiguous shorthand.  Angular momentum on the other hand, is well-defined.

Quote:

In order for the bullet to tumble end over end, it must overcome not only inertia but also the spin put on by the barrel.




I don't understand this sentence.  The angular momentum of the bullet remains the same when the bullet transitions from minor axis to major axis rotation.  The energy of the bullet also decreases slightly in the process making the process a favorable one. 

Quote:


The bullet You and dc seem to think the angular momentum will translate into end over end tumbling due to your interpretation understanding of something or other basic physics.




Fixed it for you.

Quote:

You have shown nothing to demonstrate this phenomenon or given any links.




Actually, they both provided explanations.  Two entirely different explanations that arrived at the same result.

Quote:


Did you follow that link? You are saying you know more about the subject than a physics professor? Where is your proof of that? I gave my evidence, where is yours?




Where in that link does anyone say that dark colors emit heat at a higher rate than light colors?  What I see is a statement that darker colors absorb more visible light which is turned into heat internally and then re-emitted.  So, subject to an external source of radiation, darker objects convert light into heat more rapidly.  When dealing with a blackbody, however, we aren't considering external light sources so this is completely irrelevant.

[Edit:  Last paragraph is written poorly, reader beware.  :wink:]

Edited by ChuangTzu (07/27/11 07:47 PM)

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Re: so in theory in space....... [Re: ChuangTzu]
    #14833895 - 07/27/11 03:57 PM (12 years, 9 months ago)

You guys aught to go explain to the gun makers and shooters that they are all wrong about putting spin on a bullet. They think it prevents tumbling, but you folks seem to know better than me and better than them that it's the opposite. You have explained that it promotes tumbling. I'm sure they will smack themselves in the face and say "of course, we've been doing it backwards all this time"

Hurry up before someone else tells them and maybe you can get a nobel prize or something?

And then explain to the parka makers that black does not give off any more heat than white and since it absorbs heat better, they should make winter clothing in black only. They will do the forehead smack and thank you for your help.

I'm convinced, now go out and explain it to those fools who still think the other way.

Seuss, you are convinced too aren't you? How could you doubt all that sincerity?


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Re: so in theory in space....... [Re: Stonehenge]
    #14833911 - 07/27/11 04:00 PM (12 years, 9 months ago)

Quote:

I'm convinced, now go out and explain it to those fools who still think the other way.




Thats my job.  :grin:

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Re: so in theory in space....... [Re: DieCommie]
    #14833924 - 07/27/11 04:03 PM (12 years, 9 months ago)

Quote:

DieCommie said:
Quote:

I'm convinced, now go out and explain it to those fools who still think the other way.




Thats my job.  :grin:




Physics is tough like that. :sadyes:


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Re: so in theory in space....... [Re: Doc_T]
    #14834014 - 07/27/11 04:27 PM (12 years, 9 months ago)

hard core :shrug:


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Re: so in theory in space....... [Re: Stonehenge]
    #14834291 - 07/27/11 05:26 PM (12 years, 9 months ago)

Quote:

Stonehenge said:
You guys aught to go explain to the gun makers and shooters that they are all wrong about putting spin on a bullet. They think it prevents tumbling, but you folks seem to know better than me and better than them that it's the opposite. You have explained that it promotes tumbling. I'm sure they will smack themselves in the face and say "of course, we've been doing it backwards all this time"




The physics of a bullet in an atmosphere over the course of its couple second flight time are in no way representative of the physics of a bullet in free space over the course of its multi-billion year trajectory.

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Re: so in theory in space....... [Re: Stonehenge]
    #14834420 - 07/27/11 05:51 PM (12 years, 9 months ago)

.

Edited by DieCommie (11/14/16 11:36 AM)

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Re: so in theory in space....... [Re: DieCommie]
    #14834516 - 07/27/11 06:15 PM (12 years, 9 months ago)

:thumbup:

Check out the video on the about half way down the page on the right called "6-Minute video of Astronaut Owen Garriott demonstrating the changing polhode paths of a partially-full drink bottle rotating in zero G aboard the NASA Skylab".

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Re: so in theory in space....... [Re: ChuangTzu]
    #14834757 - 07/27/11 07:03 PM (12 years, 9 months ago)

That is very interesting about polhode motion. This seems to be related to changes in torque experienced by the body. In this case a bullet. It would seem likely that some tiny wobble would be present. However, for this to progress to tumbling end over end would seem to require either outside interference or a liquid or elastic center which causes losses in torque. Where would this come from?

>It is important to note that these changes in the orientation of the body as it spins may not be due to external torques, but rather result from energy dissipated internally as the body is spinning. Even if angular momentum is conserved (no external torques), internal energy can be dissipated during rotation if the body is not perfectly rigid

Since we have no external influences that would slow it's rotation, the fact it is reasonably rigid should seem to minimize any polhode motion showing up. In the near zero temps of outer space, this would be even more so. The earth having an elastic core has a slight polhode motion. The earth is billions of years old. How many billions of years would it take for a detectable motion to be seen in the bullet? However, i commend diecommie for coming up with an interesting effect even if it does not cause the bullet to tumble end over end any time soon. Maybe after a trillion years? It's possible.

Any scientific stuff to back up the theory that black does not give off heat faster than white?


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Re: so in theory in space....... [Re: Stonehenge]
    #14834951 - 07/27/11 07:37 PM (12 years, 9 months ago)

Quote:

Stonehenge said:
That is very interesting about polhode motion. This seems to be related to changes in torque experienced by the body.




What do you mean by changes in torque?  Our analysis doesn't include any external torques.

Quote:

In this case a bullet. It would seem likely that some tiny wobble would be present. However, for this to progress to tumbling end over end would seem to require either outside interference or a liquid or elastic center which causes losses in torque. Where would this come from?




A bullet is not a rigid body.  In fact, it is less rigid than the quartz spheres in the article DieCommie linked to...

Quote:


Since we have no external influences that would slow it's rotation, the fact it is reasonably rigid should seem to minimize any polhode motion showing up.




Minimize?  What do you mean?  Making the bullet out of the most rigid material would "minimize" the rate at which this phenomenon occurs, but it would still occur.  Lead is nowhere near the most rigid material known--it's actually quite elastic.  Quartz is very, very rigid and still showed this effect very rapidly in the experiment talked about in DieCommie's link.  I would estimate that the bullet would have completely shifted its axis of rotation within minutes, rather than a trillion years as you assert.

Quote:

In the near zero temps of outer space, this would be even more so. The earth having an elastic core has a slight polhode motion.  The earth is billions of years old. How many billions of years would it take for a detectable motion to be seen in the bullet?




A tiny fraction of a billion.

Quote:

However, i commend diecommie for coming up with an interesting effect even if it does not cause the bullet to tumble end over end any time soon. Maybe after a trillion years? It's possible.




Why don't you calculate it?

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Re: so in theory in space....... [Re: DieCommie]
    #14835939 - 07/27/11 10:47 PM (12 years, 9 months ago)

Quote:

DieCommie said:
Here you go stonehenge,  http://einstein.stanford.edu/highlights/hl_polhode_story.html

It has einstein and stanford in the name so maybe you will take it more seriously than a guy named diecommie.  I like how they articulate the difference between an unstable axis of rotation and moving into a high moment of inertia configuration after losing energy.

Quote:

Every solid body inherently has three principal axes of symmetry through its center of mass, and each of these axes has a corresponding moment of inertia. The moment of inertia about an axis is a measurement of how difficult it is to accelerate the body about that axis. The closer the concentration of mass to the axis, the smaller the torque required to get it spinning at the same rate about that axis.

The shortest axis of symmetry (i.e. the axis through the center of the wood block from front to back) has the largest or maximum moment of inertia. If energy is dissipated while an object is rotating, this will cause the polhode motion about this maximum axis of inertia to damp out or stabilize, with the polhode path becoming a smaller and smaller ellipse or circle, closing in on the axis.

The intermediate axis of symmetry (e.g. the axis through the center of the block of wood, from side to side) corresponds to an intermediate moment of inertia that lies between the minimum and maximum moments of inertia. A body is never stable when spinning about this axis, and dissipated energy will cause the polhode to start migrating to the object’s axis of maximum inertia. The transition point between two stable axes of rotation is called the “separatrix,” along which the angular velocity passes through the axis of intermediate inertia.

The longest axis of symmetry (i.e. the axis through the center the wood block, from top to bottom) corresponds to the smallest or minimum moment of inertia. Rotation about this axis is also stable, but given enough time, such as a body rotating in zero g, any perturbations due to energy dissipation or torques would cause the polhode path to expand, in larger and larger ellipses or circles, and eventually migrate through the separatrix and its axis of intermediate inertia to its axis of maximum inertia.







btw whatever happened to those funny celebrity comics you used to make?? :lol:


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Re: so in theory in space....... [Re: Stonehenge]
    #14836681 - 07/28/11 02:06 AM (12 years, 9 months ago)

Quote:

Stonehenge said:

Seuss, you are convinced too aren't you? How could you doubt all that sincerity?




Rather than making irrelevant appeals, it would be helpful if you could indicate what exactly you find incorrect and how you've reached that conclusion.  I explained why I felt the way I do, and you've not taken issue with any of it except to pick at straw man arguments such as 'sincerity' and other nonsense nobody asserted was persuasive.

Quote:

DieCommie said:
"Energy of rotation" does not resist change in orientation, angular momentum does.  And the angular momentum does not change, only the axis of rotation with respect to the body.  Its in the tumbling over end that the bullet is able to maintain its angular momentum in spite of losing energy. 




I assume this tumbling would tend to be transverse to the linear momentum, right?  Since the bullet's angular momentum is initially parrallel to its linear momentum, I would assume that it would tend to retain this, given there's no aerodynamic considerations to prevent this. I couldn't tell if you were suggesting something else or not.


Quote:

Stonehenge said:
DC and john, i'm sorry you don't understand the physics of a gyroscope or how it affects the trajectory of a bullet. I provided a link but it seems to have been ignored. You can say "so what" as many times as you want but not only physicists but people in the field have proven what i said to be true.




If you have some source that is persuasive your going to have to make an argument and cite it with particularity to the relevant portion.  I'm not going to attempt to search out your argument for you in some document when I don't believe you are correct in the first place, especially not if you can't explain yourself.

Edited by johnm214 (07/28/11 02:13 AM)

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Re: so in theory in space....... [Re: johnm214]
    #14838424 - 07/28/11 11:53 AM (12 years, 9 months ago)

I remember now that i read about this years ago in regards to the earths tilt on it's axis. The axis wobbles over time and the change in the wobble was referred to as the precession of the equinoxes and would change a tiny bit over centuries.

The earth is a non rigid body, it's made up mostly of liquids in the form of melted rock and molten iron. It is flying through space, much like a bullet. The bullet has no liquids in it and would rapidly lose what little heat it had and have a temperature close to absolute zero. The earth is said to be about 8 billion years old. My question to all you out there is why hasn't the earth flipped and why isn't it tumbling end over end? It is still rotating about its axis with only a minor wobble. Perhaps in another 8 billion years it will or it might take a lot longer.

I grant you a bullet will eventually start tumbling but not in the time frame indicated. Anything that takes billions of years to be seen is what i call negligible.

OK, we are all learning some science here. Everyone has gone silent on the dark objects absorbing and giving off radiant  energy faster than white. I take it silence equals assent?


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Re: so in theory in space....... [Re: Stonehenge]
    #14838557 - 07/28/11 12:17 PM (12 years, 9 months ago)

Quote:

My question to all you out there is why hasn't the earth flipped and why isn't it tumbling end over end?




If and when the rotation slows down, it will.

Quote:

Anything that takes billions of years to be seen is what i call negligible.




Life took billions of years to be seen.  But I dont suspect it would take anywhere near that long.  Would be a fun little calculation to do.


Quote:

Everyone has gone silent on the dark objects absorbing and giving off radiant  energy faster than white. I take it silence equals assent?





Ha.  I dont know what to tell you.  You keep confusing the process of absorbing radiation with the process of emitting it as a black body.  As long as you choose not to see the difference, you will remain confused.

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Re: so in theory in space....... [Re: DieCommie]
    #14839971 - 07/28/11 04:53 PM (12 years, 9 months ago)

>Would be a fun little calculation to do.

Knock yourself out

>Ha.  I dont know what to tell you.

Fair enough

We may have explored this thread as far as it's reasonable to go.


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Re: so in theory in space....... [Re: Stonehenge]
    #14840365 - 07/28/11 06:36 PM (12 years, 9 months ago)

Still waiting on what your point of disagreement was and why, or any evidence that your point of view is correct.  Not much to talk about if you won't answer any questions or provide the basis for your claims.

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Re: so in theory in space....... [Re: Stonehenge]
    #14841123 - 07/28/11 09:44 PM (12 years, 9 months ago)

Quote:

Stonehenge said:
I remember now that i read about this years ago in regards to the earths tilt on it's axis. The axis wobbles over time and the change in the wobble was referred to as the precession of the equinoxes and would change a tiny bit over centuries.

The earth is a non rigid body, it's made up mostly of liquids in the form of melted rock and molten iron. It is flying through space, much like a bullet. The bullet has no liquids in it and would rapidly lose what little heat it had and have a temperature close to absolute zero. The earth is said to be about 8 billion years old. My question to all you out there is why hasn't the earth flipped and why isn't it tumbling end over end? It is still rotating about its axis with only a minor wobble. Perhaps in another 8 billion years it will or it might take a lot longer.

I grant you a bullet will eventually start tumbling but not in the time frame indicated. Anything that takes billions of years to be seen is what i call negligible.

OK, we are all learning some science here. Everyone has gone silent on the dark objects absorbing and giving off radiant  energy faster than white. I take it silence equals assent?




because it's perfectly balanced in precise orbit. to answer something for you, you are thinking a bullet that falls into a planets gravity or orbit won't tumble. sure it will. we are argueing that if the bullet flies through space infinitely that it will or won't tumble. I say it won't, it will follow the same path and in such as the same way that it left the gun. ever play asteroids? an object in motion tends to stay in motion, an object at rest tends to stay at rest. what would cause the bullet to change it's characteristics and tumble? air friction? doesn't exist in space? maybe tiny molecular particles broken off from the asteroid belt flowing around could. but really nothing else could. idk w/e


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Re: so in theory in space....... [Re: imachavel]
    #14842420 - 07/29/11 04:16 AM (12 years, 9 months ago)

> My question to all you out there is why hasn't the earth flipped and why isn't it tumbling end over end?

The moon.


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Re: so in theory in space....... [Re: Seuss]
    #14843053 - 07/29/11 09:51 AM (12 years, 9 months ago)

Imach, your answer flies in the face of the polhode theory which has been proven on the basis of the earth's wobble about it's axis as well as experimentally. Seuss, you haven't explained how the moon would do this.

The path of the bullet would depend on whether it escaped the gravity of the solar system as well as the gravity of planets in the system. It might go into orbit around the sun, around a planet or large asteroid. It might hit some solid object and shatter. Or, it could fly out into outer space and be pushed with a tiny acceleration by light pressure. Any pelhode wobble in it's spin would take possibly billions of years to show up. By then it may have made it to another solar system. Some poor alien might be walking along and whammo! gets hit by a chunk of lead. "where the @xF%! did that come from?"


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Re: so in theory in space....... [Re: Stonehenge]
    #14843110 - 07/29/11 10:14 AM (12 years, 9 months ago)

Nature:
Quote:

Stabilization of the Earth's obliquity by the Moon

J. Laskar, F. Joutel & P. Robutel

Astronomie et Systèmes Dynamiques, Bureau des Longitudes, 77 Avenue Denfert-Rochereau, F75014 Paris, France

ACCORDING to Milankovitch theory1,2, the ice ages are related to variations of insolation in northern latitudes resulting from changes in the Earth's orbital and orientation parameters (precession, eccentricity and obliquity). Here we investigate the stability of the Earth's orientation for all possible values of the initial obliquity, by integrating the equations of precession of the Earth. We find a large chaotic zone which extends from 60° to 90° in obliquity. In its present state, the Earth avoids this chaotic zone and its obliquity is essentially stable, exhibiting only small variations of plusminus 1.3° around the mean value of 23.3°. But if the Moon were not present, the torque exerted on the Earth would be smaller, and the chaotic zone would then extend from nearly 0° up to about 85°. Thus, had the planet not acquired the Moon, large variations in obliquity resulting from its chaotic behaviour might have driven dramatic changes in climate. In this sense one might consider the Moon to act as a potential climate regulator for the Earth.




(Obliquity is the axial tilt.)

NASA:
Quote:

The Moon is more than a pretty accessory in our night sky. It stabilizes Earth's wobble, which led to a more stable climate and probably helped life evolve. The Moon also guides the ebb and flow of Earth's oceans.




NASA:
Quote:

Does the Moon stabilize Earth in its rotation?

Well, I'm no expert on motions of the Earth, but the Moon does add drag to the Earth's rotation in the form of tides, both oceanic and internal. This added drag tends to stabilize the rotation. It is also gradually slowing down the rotation of the Earth, which gradually lengthens Earth days.

Dr. Eric Christian and Beth Barbier




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Re: so in theory in space....... [Re: Seuss]
    #14843162 - 07/29/11 10:42 AM (12 years, 9 months ago)

Seuss, that's interesting. But they couch it in terms of "may" stabilize the earth's tilt and climate variations. However, in the explanation of polhode wobble, they say that internal or external changes in torque drive the polhode effect. For example, movements of internal liquid can cause a loss of spin which would give more wobble. The moon exerting a drag would seem to be an external force which would drive it further. We seem to have competing theories here. Why would an external drag not add to the polhode effect? All i see above is the statement that it stabilizes but no hard facts to back it up. Sounds like speculation.

I quote from the source dc gave:

>The longest axis of symmetry (i.e. the axis through the center the wood block, from top to bottom) corresponds to the smallest or minimum moment of inertia. Rotation about this axis is also stable, but given enough time, such as a body rotating in zero g, any perturbations due to energy dissipation or torques would cause the polhode path to expand, in larger and larger ellipses or circles, and eventually migrate through the separatrix and its axis of intermediate inertia to its axis of maximum inertia.


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Re: so in theory in space....... [Re: Stonehenge]
    #14843192 - 07/29/11 10:50 AM (12 years, 9 months ago)

So which axis for an oblate spheroid corresponds to the smallest moment of inertia?  Are you sure you are considering the right axis?  Think about it for a bit.  This might help, http://en.wikipedia.org/wiki/Ellipsoid

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Re: so in theory in space....... [Re: DieCommie]
    #14866677 - 08/03/11 10:47 AM (12 years, 9 months ago)

I know this isn't quite on topic, but as it's related, I thought I would ask.

As there's no convection in space, and therefor cooling is very slow, how would it feel to put... say your hand into space? I guess after a number of seconds you would get 'the bends' in your hand, and that would cause some type of feeling associated with that effect, but how would the temperature feel on your hand?

I guess the thing that makes me wonder this, is all the time on Earth, we're having molecules hitting our skin (from clothing, air, water, etc), so I wonder if it would be a noticeable difference if someone placed their hand in space, and no molecules were hitting their hand.

Thoughts, anyone?

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Re: so in theory in space....... [Re: HeavyToilet]
    #14866856 - 08/03/11 11:41 AM (12 years, 9 months ago)

Quote:

HeavyToilet said:
I know this isn't quite on topic, but as it's related, I thought I would ask.

As there's no convection in space, and therefor cooling is very slow, how would it feel to put... say your hand into space? I guess after a number of seconds you would get 'the bends' in your hand, and that would cause some type of feeling associated with that effect, but how would the temperature feel on your hand?

I guess the thing that makes me wonder this, is all the time on Earth, we're having molecules hitting our skin (from clothing, air, water, etc), so I wonder if it would be a noticeable difference if someone placed their hand in space, and no molecules were hitting their hand.

Thoughts, anyone?




It would feel like when you put your hand over the end of a vacuum cleaner except that pink circle that you get on your hand after doing that would cover your whole hand.  Whatever you had sealing the rest of your arm off from the vacuum would get really tight when your hand swelled and it would cut off circulation to your hand.  It would be very painful and I doubt you'd notice the temperature effects.

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Re: so in theory in space....... [Re: ChuangTzu]
    #14866884 - 08/03/11 11:48 AM (12 years, 9 months ago)

I'm thinking about more of an idealized situation. Like if there was such a way that you could have some kind of seal that would have your hand in outer space, but the rest of your body inside, and the seal wasn't strong enough to cut off circulation, but would prevent the oxygen and whatnot from rushing out.

I know such a thing would probably be impossible to set up, but I'm just wondering exclusively about the temperature, or lack of feeling of molecules constantly bumping into the skin, rather than considering all the issues with setting up such a situation.

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Re: so in theory in space....... [Re: ChuangTzu]
    #14866886 - 08/03/11 11:48 AM (12 years, 9 months ago)

The water in your blood in the hand would tend to boil in the zero pressure of space. Unless it had sun shining on it it would get cold really fast. If it did have sun shining on it you would pick up a nasty burn in short order. Now picture yourself trying to get your hand back out and it's stuck. If you did pull it out the air in the cabin would fly out the hole unless it was quickly plugged.


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Re: so in theory in space....... [Re: HeavyToilet]
    #14866892 - 08/03/11 11:51 AM (12 years, 9 months ago)

Quote:

HeavyToilet said:
I know such a thing would probably be impossible to set up, but I'm just wondering exclusively about the temperature, or lack of feeling of molecules constantly bumping into the skin, rather than considering all the issues with setting up such a situation.




The lack of molecules bumping into the skin is exactly the feeling of your hand swelling up like a balloon that I described.

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Re: so in theory in space....... [Re: Stonehenge]
    #14870659 - 08/04/11 03:42 AM (12 years, 9 months ago)

Quote:

HeavyToilet said:
I'm thinking about more of an idealized situation. Like if there was such a way that you could have some kind of seal that would have your hand in outer space, but the rest of your body inside, and the seal wasn't strong enough to cut off circulation, but would prevent the oxygen and whatnot from rushing out.

I know such a thing would probably be impossible to set up, but I'm just wondering exclusively about the temperature, or lack of feeling of molecules constantly bumping into the skin, rather than considering all the issues with setting up such a situation.





Ignoring the pressure change and all that entails, I would imagine you wouldn't feel much of anything, as if you were in room temperature, followed by a very gradual decrease in temperature due to radiative heat loss (your skin putting off more radiative energy than it takes in per period of time and thus the temperature decreasing).  Of course, your blood stream would almost certainly provide many orders of magnitude more heat to the tissue than is lossed in radiative heat loss, so perhaps nothing at all.


Quote:

Stonehenge said:
The water in your blood in the hand would tend to boil in the zero pressure of space.





Naw, that's just an old myth.  Your blood isn't in the zero pressure of space, its in your blood vessels which are in your hand. If your blood vessels and tissueshave the integrity to maintain their shape and function during normal activities, they certainly have the integrity to resist to some degree the huge loss of pressure which would be required to bring the water in the mixture to the boiling point.  Add in the other tissues which the vessels are imbedded into, and its obvious there's no way the pressure in your hand is going to drop to below boiling pressure for water at physiological temp, much less whatever temp is required to boil the mixture that is blood.

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Re: so in theory in space....... [Re: johnm214]
    #14870768 - 08/04/11 05:00 AM (12 years, 9 months ago)

>> The water in your blood in the hand would tend to boil in the zero pressure of space.
> Naw, that's just an old myth.

You are both correct... This has been well documented by NASA and the Soviet Union through various accidents where people were exposed to a hard vacuum (and most lived to tell the tale).  See http://www.damninteresting.com/outer-space-exposure/ for more details.


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Re: so in theory in space....... [Re: Seuss]
    #14870830 - 08/04/11 05:36 AM (12 years, 9 months ago)

Hmm, are you suggesting there's some merit to the claim that the blood would tend to boil in a hand exposed to space?

That's an interesting article (wasn't aware there were real-world examples of this occurring) but I didn't see any mention of boiling blood inside the body.  The closest was mention of pressure's effect on solubility of gasses, but that's not boiling (the gasses are already far past their boiling temperature at both terrestrial and space conditions, obviously).

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Re: so in theory in space....... [Re: johnm214]
    #14870845 - 08/04/11 05:48 AM (12 years, 9 months ago)

> Hmm, are you suggesting there's some merit to the claim that the blood would tend to boil in a hand exposed to space?

Yes, a tiny bit of merit (though I was thinking of an entire body exposed, not just a hand). Length of exposure and a beating heart would be large mitigating factors.  A few seconds of exposure (to a hard vacuum) of a hand attached to a living body isn't going to cause blood to boil.

I could be wrong... :smile:

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Re: so in theory in space....... [Re: Seuss]
    #14871544 - 08/04/11 10:14 AM (12 years, 9 months ago)

Quote from the link

>in the absence of atmospheric pressure water will spontaneously convert into vapor, which would cause the moisture in a victim’s mouth and eyes to quickly boil away. The same effect would cause water in the muscles and soft tissues of the body to evaporate, prompting some parts of the body to swell to twice their usual size after a few moments

>>Stonehenge said:
The water in your blood in the hand would tend to boil in the zero pressure of space.


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Re: so in theory in space....... [Re: Stonehenge]
    #14871927 - 08/04/11 11:56 AM (12 years, 9 months ago)

For what its worth, some guy on NASA's site agree's with me: 

Quote:

If you don't try to hold your breath, exposure to space for half a minute or so is unlikely to produce permanent injury. Holding your breath is likely to damage your lungs, something scuba divers have to watch out for when ascending, and you'll have eardrum trouble if your Eustachian tubes are badly plugged up, but theory predicts -- and animal experiments confirm -- that otherwise, exposure to vacuum causes no immediate injury. You do not explode. Your blood does not boil. You do not freeze. You do not instantly lose consciousness.


emphasis added

http://imagine.gsfc.nasa.gov/docs/ask_astro/answers/970603.html

Quote:

Stonehenge said:
Quote from the link

>in the absence of atmospheric pressure water will spontaneously convert into vapor, which would cause the moisture in a victim’s mouth and eyes to quickly boil away. The same effect would cause water in the muscles and soft tissues of the body to evaporate, prompting some parts of the body to swell to twice their usual size after a few moments

>>Stonehenge said:
The water in your blood in the hand would tend to boil in the zero pressure of space.




How does that quote back up your claim?  The cited examples refer to water located on external surfaces which would be exposed to the vacuum to some extent.  The water in your blood in your hand is not on an external surface which would be exposed to the vacuum to some extent.

What evidence of your claim do you have?

A bit technical, and perhaps the article's author didn't want to get into such things, but water spontaneously evaporating is not boiling.  Boiling is when the partial pressure of the liquid equals/exceeds the atmospheric pressure.  Spontaneous vaporization can occur for any number of reasons at below the boiling point.

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Re: so in theory in space....... [Re: johnm214]
    #14872038 - 08/04/11 12:21 PM (12 years, 9 months ago)

Ive never heard that the blood would boil (except for movies), and I dont see why it would.  Your skin is still keeping it under pressure.  Ill read some of those links later.

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Re: so in theory in space....... [Re: johnm214]
    #14872070 - 08/04/11 12:26 PM (12 years, 9 months ago)

Quote:

johnm214 said:
A bit technical, and perhaps the article's author didn't want to get into such things, but water spontaneously evaporating is not boiling.  Boiling is when the partial pressure of the liquid equals/exceeds the atmospheric pressure.  Spontaneous vaporization can occur for any number of reasons at below the boiling point.




A bit technical, but I think you meant that boiling is when the vapor pressure of the substance equals/exceeds the atmospheric pressure.  :wink:

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Re: so in theory in space....... [Re: ChuangTzu]
    #14872338 - 08/04/11 01:15 PM (12 years, 9 months ago)

"exposure to vacuum causes no immediate injury"

No one said it was immediate. And anyway the guy is just estimating

>How does that quote back up your claim?  The cited examples refer to water located on external surfaces which would be exposed to the vacuum to some extent.  The water in your blood in your hand is not on an external surface which would be exposed to the vacuum to some extent.

>>The same effect would cause water in the muscles and soft tissues of the body to evaporate, prompting some parts of the body to swell to twice their usual size after a few moments.

If anyone thinks the skin or outer tissues will maintain normal pressure on internal parts, they are welcome to try exposing themselves to a vacuum though i don't recommend it.


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Re: so in theory in space....... [Re: Stonehenge]
    #14872452 - 08/04/11 01:44 PM (12 years, 9 months ago)

Quote:

ChuangTzu said:
Quote:

johnm214 said:
A bit technical, and perhaps the article's author didn't want to get into such things, but water spontaneously evaporating is not boiling.  Boiling is when the partial pressure of the liquid equals/exceeds the atmospheric pressure.  Spontaneous vaporization can occur for any number of reasons at below the boiling point.




A bit technical, but I think you meant that boiling is when the vapor pressure of the substance equals/exceeds the atmospheric pressure.  :wink:




lol, yeah, you're correct of course: the partial pressure of the gas component


Quote:

Stonehenge said:
"exposure to vacuum causes no immediate injury"

No one said it was immediate. And anyway the guy is just estimating




I'm not claiming that particular assertion is disputed.  It was included as it was part of the discussion which claimed the blood would not boil when a person is exposed to space.

Quote:

>How does that quote back up your claim?  The cited examples refer to water located on external surfaces which would be exposed to the vacuum to some extent.  The water in your blood in your hand is not on an external surface which would be exposed to the vacuum to some extent.

>>The same effect would cause water in the muscles and soft tissues of the body to evaporate, prompting some parts of the body to swell to twice their usual size after a few moments.

If anyone thinks the skin or outer tissues will maintain normal pressure on internal parts, they are welcome to try exposing themselves to a vacuum though i don't recommend it.





I'm not sure what the relevance of your reply is.  I asked what the source mentioned by Seuss that you cited had to do with your claim: it didn't seem to justify it.  Further, I've asked what the basis for your claim that the blood in your hand would boil if your hand was exposed to space.  You have not answered.

Please provide the justification for your claim.

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Re: so in theory in space....... [Re: johnm214]
    #14872488 - 08/04/11 01:52 PM (12 years, 9 months ago)

john, i know you can read so i must assume its your pride which prevents you from admitting you were wrong. No one goes very long without being wrong unless they say nothing. We can quibble about whether rapid evaporation is the same as boiling but there is no point in it. Believe what you wish, i'm done with that particular topic.


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Re: so in theory in space....... [Re: Stonehenge]
    #14872517 - 08/04/11 02:00 PM (12 years, 9 months ago)

Quote:

Stonehenge said:
john, i know you can read so i must assume its your pride which prevents you from admitting you were wrong.




Lame, as usual.

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Re: so in theory in space....... [Re: Stonehenge]
    #14872520 - 08/04/11 02:00 PM (12 years, 9 months ago)

Quote:

Stonehenge said:
john, i know you can read so i must assume its your pride which prevents you from admitting you were wrong. No one goes very long without being wrong unless they say nothing. We can quibble about whether rapid evaporation is the same as boiling but there is no point in it. Believe what you wish, i'm done with that particular topic.




I didn't really care about this particular subject, but john is right that you erroneously used Seuss's link as support for your claim.  The quoted portion of the text doesn't talk about blood boiling.  It mentions liquids outside the blood vessels which aren't constrained by the body's vasculature.  Furthermore, a hand exposed to vacuum is still connected to the rest of the rest of the body which is still at pressure.  Either the blood inside the hand stays at pressure, or the hand bursts.  The blood would not boil unless the hand burst.

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Re: so in theory in space....... [Re: Stonehenge]
    #14872616 - 08/04/11 02:22 PM (12 years, 9 months ago)

Quote:

Stonehenge said:
john, i know you can read so i must assume its your pride which prevents you from admitting you were wrong. No one goes very long without being wrong unless they say nothing. We can quibble about whether rapid evaporation is the same as boiling but there is no point in it. Believe what you wish, i'm done with that particular topic.




If this isn't a prideful post I don't know what is. :lol:

Quote:

johnm214 said:
Quote:

HeavyToilet said:
I'm thinking about more of an idealized situation. Like if there was such a way that you could have some kind of seal that would have your hand in outer space, but the rest of your body inside, and the seal wasn't strong enough to cut off circulation, but would prevent the oxygen and whatnot from rushing out.

I know such a thing would probably be impossible to set up, but I'm just wondering exclusively about the temperature, or lack of feeling of molecules constantly bumping into the skin, rather than considering all the issues with setting up such a situation.





Ignoring the pressure change and all that entails, I would imagine you wouldn't feel much of anything, as if you were in room temperature, followed by a very gradual decrease in temperature due to radiative heat loss (your skin putting off more radiative energy than it takes in per period of time and thus the temperature decreasing).  Of course, your blood stream would almost certainly provide many orders of magnitude more heat to the tissue than is lossed in radiative heat loss, so perhaps nothing at all.




Thank you John, I figured as much... makes sense! :thumbup:

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Re: so in theory in space....... [Re: HeavyToilet]
    #14872652 - 08/04/11 02:34 PM (12 years, 9 months ago)

Your ears would probably pop like mad though huh?  Eyeballs seem like they could be very pressure sensitive (maybe Im just thinking of Total Recall? :lol:)  I wonder about your breath?  How hard would it be to maintain a pressure difference with your mouth?  (Maybe Ill ask some girls at work :wink:)

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Re: so in theory in space....... [Re: DieCommie]
    #14872767 - 08/04/11 02:56 PM (12 years, 9 months ago)

Now, these are the experiments they should be conducting on the International Space Station! I can just imagine a bunch of Russians taking turns sticking their heads out into space. :grin:

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Re: so in theory in space....... [Re: HeavyToilet]
    #14872844 - 08/04/11 03:09 PM (12 years, 9 months ago)

I'm pretty sure they did do these experiments.  With animals.

Edit: for example: http://www.ncbi.nlm.nih.gov/pubmed/5972265

Edited by ChuangTzu (08/04/11 03:12 PM)

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Re: so in theory in space....... [Re: ChuangTzu]
    #14872872 - 08/04/11 03:14 PM (12 years, 9 months ago)

Quote:

ChuangTzu said:
I'm pretty sure they did do these experiments.  With animals.




Or on humans in large vacuum chambers before space flight.  I would guess from some Mengele like character.

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Re: so in theory in space....... [Re: DieCommie]
    #14873105 - 08/04/11 04:17 PM (12 years, 9 months ago)

Chuang wrote:

>you erroneously used Seuss's link as support for your claim.  The quoted portion of the text doesn't talk about blood boiling.  It mentions liquids outside the blood vessels which aren't constrained by the body's vasculature.

So you don't think water spontaneously turning into vapor is another term for boiling? You want to see a pot with bubbles coming up from the bottom before you call it boiling? You did see the part where they said the muscles and soft tissues would swell up after a few moments? Notice i didn't give a time frame for this to happen nor did i say the hand would explode. It would rapidly swell due to the water rapidly turning into vapor which everyplace else is considered boiling. You think the thin walls of the blood vessels would withstand a pressure difference of nearly 15 lb per sq inch? If they could do that, then why would the hand swell so rapidly?

It seems we have a dispute over what constitutes boiling. I say it's water turning rapidly into vapor which usually has bubbles as part of the process. Are you saying there would be no bubbles or what is the argument being made that the blood would not boil?

Here is a link which shows that the temperature at which water will boil is -70f in a hard vacuum

http://www.engineersedge.com/h2o_boil_pressure.htm

The blood in the hand being at a temperature some 160 degrees higher than the boiling point will surely boil. Doesn't that make sense? It may take a few moments for the blood to boil since the link seuss gave said it took a few moments for the tissues to swell but i don't see how you can get around it boiling. If it's still attached to the body the poor person will find his blood spurting out as the blood vessels disintegrate and he needs to close that opening and give up the hand if need be. Not an experiment i'd like to try.


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Re: so in theory in space....... [Re: Stonehenge]
    #14873232 - 08/04/11 04:52 PM (12 years, 9 months ago)

Quote:

Stonehenge said:
So you don't think water spontaneously turning into vapor is another term for boiling?




Sometimes it is, sometimes it isn't.  Every liquid is vaporizing and re-condensing all the time at some rate.

Quote:


You did see the part where they said the muscles and soft tissues would swell up after a few moments?




Yes, it's talking about interstitial fluids.  Where did it say that blood, which is contained in pressurized vessels, would do this?

Quote:

Notice i didn't give a time frame for this to happen nor did i say the hand would explode.




So what?

Quote:

It would rapidly swell due to the water rapidly turning into vapor




Why do you think that water is coming from the blood?

Quote:


You think the thin walls of the blood vessels would withstand a pressure difference of nearly 15 lb per sq inch?




It's irrelevant what I think.  I'm just saying that you failed to support your argument. 

Quote:


It seems we have a dispute over what constitutes boiling.




Perhaps, but that is not at issue here.  That's a completely separate matter.  Your argument was not supported by Seuss's link.  Anything else you bring up is just a distraction.

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Re: so in theory in space....... [Re: ChuangTzu]
    #14873310 - 08/04/11 05:07 PM (12 years, 9 months ago)

Ask me if i care about your opinion? Base it on facts and we will get somewhere. You simply nay say everything which is boring. I say i have amply supported the fact that the blood boils when exposed to space. You have shown no evidence that blood vessels are able to withstand those forces.

And when you say no it isn't

My reply is "yes it is"


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Re: so in theory in space....... [Re: Stonehenge]
    #14873470 - 08/04/11 05:47 PM (12 years, 9 months ago)

Quote:

Stonehenge said:
Ask me if i care about your opinion?




Your previous post repeatedly asked me what I think.  That is you (seemingly) caring about my opinion.  Regardless, I never actually provided my opinion so I have no idea what you're talking about.  My issue is with the way you form arguments, not with your positions. 

Quote:


You simply nay say everything which is boring.




No, I point out where you don't make sense.

Quote:

You have shown no evidence that blood vessels are able to withstand those forces.




Why should I provide this evidence?

Quote:


And when you say no it isn't

My reply is "yes it is"




:cactuarrun:

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Re: so in theory in space....... [Re: Stonehenge]
    #14874793 - 08/04/11 11:42 PM (12 years, 9 months ago)

Quote:

Stonehenge said:
The water in your blood in the hand would tend to boil in the zero pressure of space. Unless it had sun shining on it it would get cold really fast. If it did have sun shining on it you would pick up a nasty burn in short order. Now picture yourself trying to get your hand back out and it's stuck. If you did pull it out the air in the cabin would fly out the hole unless it was quickly plugged.




I don't believe this is entirely true. in space there is no convection, no air, I believe the correct way to say it is things would cool off slower and warm up faster. I think I mentioned this earlier in the post. if you put your hand out side the ship in micro gravity and no pressure, and the pressure didn't cause the blood in your hand to boil, which would be presented if your hand wasn't outside in the vacuum, I believe your hand would stay warm for a little longer then it would in absolute zero temperatures on earth.

but then again the atmosphere also holds in heat, so perhaps the temperature would be sucked out immediately in the vacuum. I suppose if your hand was sealed though, it would act like a thermas, taking forever to cool down. once it did though, it would reach absolute zero, unless the sun came up before that temperature could be achieved. I wonder if apollo 11 and apollo 12 or whoever it was that made it to the moon, took temperature readings of the soil on the moon before and after the sun came up, or went down, to see how long it would take for the temperature of the soil to cool down. I'm guessing below the surface of the moon a mile or so, the temperature has probably remained the same since the moon cooled down. whatever that may be, as there are no 'seasons' on the moon, only night and day and no atmosphere.

about the vacuum thing, yes your blood would boil, but it wouldn't boil until the vacuum broke open your blood vessels. remember, you have internal pressure, and it is mostly sealed. not your internal pressure wouldn't last long once he vacuum rips you apart, from what I heard you'd need to breathe out all your air and not hold your breath or your lungs would be ripped open from the loss of pressure.


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Re: so in theory in space....... [Re: johnm214]
    #14874867 - 08/04/11 11:58 PM (12 years, 9 months ago)

Quote:

johnm214 said:
For what its worth, some guy on NASA's site agree's with me: 

Quote:

If you don't try to hold your breath, exposure to space for half a minute or so is unlikely to produce permanent injury. Holding your breath is likely to damage your lungs, something scuba divers have to watch out for when ascending, and you'll have eardrum trouble if your Eustachian tubes are badly plugged up, but theory predicts -- and animal experiments confirm -- that otherwise, exposure to vacuum causes no immediate injury. You do not explode. Your blood does not boil. You do not freeze. You do not instantly lose consciousness.


emphasis added

http://imagine.gsfc.nasa.gov/docs/ask_astro/answers/970603.html

Quote:

Stonehenge said:
Quote from the link

>in the absence of atmospheric pressure water will spontaneously convert into vapor, which would cause the moisture in a victim’s mouth and eyes to quickly boil away. The same effect would cause water in the muscles and soft tissues of the body to evaporate, prompting some parts of the body to swell to twice their usual size after a few moments

>>Stonehenge said:
The water in your blood in the hand would tend to boil in the zero pressure of space.




How does that quote back up your claim?  The cited examples refer to water located on external surfaces which would be exposed to the vacuum to some extent.  The water in your blood in your hand is not on an external surface which would be exposed to the vacuum to some extent.

What evidence of your claim do you have?

A bit technical, and perhaps the article's author didn't want to get into such things, but water spontaneously evaporating is not boiling.  Boiling is when the partial pressure of the liquid equals/exceeds the atmospheric pressure.  Spontaneous vaporization can occur for any number of reasons at below the boiling point.




the greater mass of water may not boil, but I don't know where people get the idea that water can go straight to vapor form. it boils first. if only for a millionth of a second before it vaporizes it boils. and yes i've seen experimental videos of people putting water in a vacuum chamber, and before it vaporizes it boils momentarily. also it actually loses heat instead of gaining it, and ice crystals form as it boils. intense, water only exists in liquid form instead of solid or gas in a pressurized environment. funny though, in space ice crystals bounce around all the time, you'd think the sun would warm up the ice and cause it to vaporize. I suppose there is answer, I can't explain it.

no, you wouldn't immediately freeze, burn, boil, or what not in zero gravity zero pressure. but your ear drums would rupture, and your lungs would break like you said if there was no pressure. but this is only momentarily. nasa is probably assuming you will find another sealed exposure within minutes.

those same people experimenting on animals have seen the animals blood vessels rupture and their body turn into a giant bruise. I'm assuming in a vacuum the pressure would start dropping out of your pours, the oxygen would start getting sucked out through your pores slowly. on earth this happens at such a slow extent, and the massive pressure slows it down, also you keep breathing and circulating more oxygen. in space you have a problem, whatever pressure is released slowly from your pours, will get sucked out in seconds. I don't know if it would take awhile, or be very quick, but eventually your blood would form bubbles, that would cause you to swell.eventually your blood would boil when your body can't contain the pressure.

remember in space there is no temperature. temperature is measured by atoms vibrating. there is really no cold, only lack of heat. so by default in space with no sun light the temperature is automatically absolute zero. your body on earth absorbs light and your molecules heat up. like wise people use something called laser cooling which creates an opposite effect, somehow the lasers block any light from being absorbed into an object, and the temperature drops very quickly. without convection your body wouldn't cool down very quickly, as in space no molecules equal no temperature. but how long can your body without pressure hold in it's own heat? it might take a bit to cool down, but you would eventually make frozen meat in the freezer look like it's boiling in a pot compared to how frozen you would become.

I'm assuming the pressure in space at the international space station, is what keeps the temperature inside maintained. it is not absolute zero out side of the ship, there is no temperature out side of the ship. only with molecular movement, can temperature be achieved, inside the ship your worst worry would be the sun heating up the hull so badly that the inside of the ship cooks. as long as no pressure is released however, I can't imagine how the ship would cool down. however does that mean the hull wouldn't cool down? good question yes it probably would get very cold without outside temperature, the hull itself would have nothing to keep it warm, aside from the inner temperature being transferred to the hull.

I don't know this all gets confusing, I suppose there is a science class that explains it, or videos online I just don't know where to find them.


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Re: so in theory in space....... [Re: imachavel]
    #14874881 - 08/05/11 12:01 AM (12 years, 9 months ago)

Quote:

remember in space there is no temperature.




Sure there is.  You dont need atoms to have temperature, you need only energy density.  The temperature of space is about 4K, due to its energy density.

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Re: so in theory in space....... [Re: HeavyToilet]
    #14874900 - 08/05/11 12:04 AM (12 years, 9 months ago)

Quote:

HeavyToilet said:
Now, these are the experiments they should be conducting on the International Space Station! I can just imagine a bunch of Russians taking turns sticking their heads out into space. :grin:




I should have read all this before I replied. it looks like everything I said was already stated before hand. yes your hand would hold in the pressure of your blood as long as your hand maintained internal pressure. how long would that be in a vacuum? amazing.


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Re: so in theory in space....... [Re: DieCommie]
    #14874921 - 08/05/11 12:10 AM (12 years, 9 months ago)

Quote:

DieCommie said:
Quote:

remember in space there is no temperature.




Sure there is.  You dont need atoms to have temperature, you need only energy density.  The temperature of space is about 4K, due to its energy density.




no shit. but that's gotta be the energy density around this part of the solar system or galaxy. now way out in space beyond the milky way, is there any energy at all? the temperature of energy density must have nowhere near the same physical laws as temperature with extreme matter density such as it exists here on earth. what cools faster, a thermometer left under the ground in cold soil, or held in the air? I actually don't know, I'm asking, but I assume because of the density of mercury, the results will be the same, because the mercury is what's cooling, not the soil or air. at least that's what you are measuring.

now if there was a way to measure temperature directly, which would cool faster, the air or ground? or is pressure between air and ground at sea level basically the same? there is probably no way to get accurate reading on earth huh on which would cool faster?


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Re: so in theory in space....... [Re: imachavel]
    #14875171 - 08/05/11 01:21 AM (12 years, 9 months ago)

Quote:

imachavel said:
what cools faster, a thermometer left under the ground in cold soil, or held in the air?




A thermometer left under the ground because soil has a much higher heat capacity and thermal conductivity than air (assuming reasonably still air). 

Quote:

now if there was a way to measure temperature directly, which would cool faster, the air or ground?




This is a totally different question and the answer depends on lots of specifics like how you are heating each, surface area, volumes, etc.

Quote:

or is pressure between air and ground at sea level basically the same?




Yes.

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Re: so in theory in space....... [Re: Stonehenge]
    #14876250 - 08/05/11 10:42 AM (12 years, 9 months ago)

Quote:

Stonehenge said:
john, i know you can read so i must assume its your pride which prevents you from admitting you were wrong. No one goes very long without being wrong unless they say nothing.




Please confine yourself to discussing the arguments and ideas expressed by the posters.  Your feelings on fellow poster's personality and motivations are not relevant to this thread nor this forum's topic- it also tends to cause off topic arguments and more insults.


Quote:

We can quibble about whether rapid evaporation is the same as boiling but there is no point in it. Believe what you wish, i'm done with that particular topic.




?  Boiling points are pretty well defined: that point where the partial pressure of a liquid's vapor equals the atmospheric pressure.  "Rapid Evaporation" happens in many circumstances below the boiling point, such as with a closed system with a dry atmosphere and some water, say at standard conditions.

What exactly are you claiming is going to happen, if not "boiling"?  Clearly "rapid evaporation" cannot occur for very long as the physical integrity of the hand would have to be compromised to allow even a small portion of the blood to vaporize- the volume difference between the vaporized and liquid water being so great.  ChuangTzu went over all this before, and you seem to have left this point unchallenged, so its unclear what your saying.

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Re: so in theory in space....... [Re: johnm214]
    #14876380 - 08/05/11 11:26 AM (12 years, 9 months ago)

So you use your capacity as a moderator to give me an official warning basically for disagreeing with you. I suppose i'll get another one for this post but it's the truth.


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Re: so in theory in space....... [Re: Stonehenge]
    #14876455 - 08/05/11 11:43 AM (12 years, 9 months ago)

Yeah, it must be due to you disagreeing with him. It couldn't possibly due to your numerous attempts at derailing the discussion combined with a personal attack. :lol:

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Re: so in theory in space....... [Re: Stonehenge]
    #14876466 - 08/05/11 11:45 AM (12 years, 9 months ago)

Was that why you were warned- for disagreeing with me?

Quote:

Stonehenge,
Please do not insult other posters and confine your discussion to the topic of the forum and thread in question.  In general, you may criticize and discuss the ideas of posters without limit, but you may not make negative personal comments or try and change the discussion from the merits of various ideas to the personal qualities of forum members. 

This warning is based on the following two posts:

Quote:

Stonehenge said:
Ask me if i care about your opinion?[...]



http://www.shroomery.org/forums/showflat.php/Number/14873310#14873310

Quote:

Stonehenge said:
john, i know you can read so i must assume its your pride which prevents you from admitting you were wrong.[...]



http://www.shroomery.org/forums/showflat.php/Number/14872488#14872488

If you need any help understanding the rules or with anything else, please feel free to contact me or any other moderator.

-johnm214
:cheers:




Hmm, where did it mention anything about disagreements?  In fact, I thought I explicitly said that was ok?

If you want to bitch, either confine it to the feedback/complaints thread in my journal, send me a PM stating your disagreement, or send in a support ticket.

Quote:

Stonehenge said:
I suppose i'll get another one for this post but it's the truth.




Naw, if you're intent on getting yourself banned to justify your persecution complex, your going to have to do better than that :thumbup:

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Re: so in theory in space....... [Re: johnm214]
    #14876614 - 08/05/11 12:20 PM (12 years, 9 months ago)

So "Ask me if i care about your opinion?" can't be said anymore?

Saying your pride prevents you from admitting you were wrong is now an offense? Or only if a mod is involved?

I see stronger stuff than that every day on these boards, we all do. In most big forums they have a rule that a mod can not moderate in a thread that he/she is involved in. That is to prevent a hot headed response.

In this same thread diecommie said

>Lame, as usual

Which is clearly a personal attack but it supported john so no warning. I personally think minor stuff like that is no big deal. It's selective enforcement that is wrong.

In another thread i read today someone said someone else had the brains of a cow. Normally, if a mod thinks a conversation is getting too heated, he will tell everyone to knock it off. Curse words are used fairly frequently and usually receive no notice. But if you use the world "pride" and a mod doesn't like it, it can be an official offense. Selective enforcement by someone with a motive to be harsh is wrong.


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Re: so in theory in space....... [Re: Stonehenge]
    #14876711 - 08/05/11 12:43 PM (12 years, 9 months ago)

Quote:

Which is clearly a personal attack but it supported john so no warning.




I dont think it is.  Your response and ideas are lame.  I dont know anything about you personally.

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Re: so in theory in space....... [Re: Stonehenge]
    #14876714 - 08/05/11 12:44 PM (12 years, 9 months ago)

Quote:

Stonehenge said:
So "Ask me if i care about your opinion?" can't be said anymore?




Quote:


Saying your pride prevents you from admitting you were wrong is now an offense? Or only if a mod is involved?




This has nothing to do with the scientific discussion we are having.

Quote:

I see stronger stuff than that every day on these boards, we all do. In most big forums they have a rule that a mod can not moderate in a thread that he/she is involved in. That is to prevent a hot headed response.



This forum is for scientific discussion, those forums are not. :shrug:

Quote:


In this same thread diecommie said

>Lame, as usual

Which is clearly a personal attack but it supported john so no warning.




It looks like to me that he was responding to your post. He was not saying that you, as a human being are lame. It was pretty obvious he was calling your tactic of side stepping, and attacking John personally, rather than discussing the topic, lame.

Edited by HeavyToilet (08/05/11 12:47 PM)

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Re: so in theory in space....... [Re: Stonehenge]
    #14877623 - 08/05/11 04:23 PM (12 years, 9 months ago)

Again: take it somewhere else.

As for diecommie's statement, report it if you think there's a problem.  I don't see why this is such a big mystery though: attacking a person's post is perfectly fine, attacking their person is not.  He can call your post lame if he wants to.

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Re: so in theory in space....... [Re: johnm214]
    #14878961 - 08/05/11 09:36 PM (12 years, 9 months ago)

yes please. this thread has been derailed by moderators and shroomery members. what does any of this have to do with an object traveling in space, or the way an object would travel in space due to loss of atmospheric pressure? cmon


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Re: so in theory in space....... [Re: imachavel]
    #14879545 - 08/06/11 12:42 AM (12 years, 9 months ago)

Quote:

imachavel said:
if I had a space ship that was 5 miles away from a grenade, and this grenade exploded, in theory, it would travel at the same speed for 5 miles and hit my space ship as though it had exploded right next to it.

without air friction, or gravity, objects in motion tend to stay in motion. this is how the voyager got to pluto with a few rocket corrections right? objects in motion tend to stay in motion makes so much more sense in space




okay how am i going to explain this in text....the answer is yes and no...gravity affects everything...that is why we will use gravity to slingshot off of planets and such....as you are moving the gravity will slow you down gradually...explosions have never been 'tested' in outer space(which is why we are afraid to use nuclear energy in space) honestly even with my experience in science and physics im unsure on what to say...it could explode and then implode on itself  :shrug: it may not even explode at all! space is a vaccum, and when you pull the pin on a grenade it releases a spring mechanism that pushes the pin into a peice of metal which creates a spark, lights the fuse, and in 5 seconds it goes BOOM! theres two things that would cause me to think that your idea wouldnt work...

1. How would the absence of gravity affect the grenades spring mechanism?
2. well the grenade be able to produce a spark to ignite the fuse and can that fuse stay ignited....i dont believe the fuse would become ignited and even if it did become ignited it the fuse would become snuffed out because space is a vaccum...

but HEY! who knows! we are constantly discovering new things about space so maybe everything i said is wrong but im about 80% sure what i said is right :grin:


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Re: so in theory in space....... [Re: GrimReaper6942]
    #14879548 - 08/06/11 12:44 AM (12 years, 9 months ago)

Quote:

1. How would the absence of gravity affect the grenades spring mechanism?




It wouldn't.  Springs dont need gravity to compress or expand.

Quote:

2. well the grenade be able to produce a spark to ignite the fuse and can that fuse stay ignited....i dont believe the fuse would become ignited and even if it did become ignited it the fuse would become snuffed out because space is a vaccum...




You could put the oxygen in the fuel/explosive material, like a rocket engine.

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Re: so in theory in space....... [Re: DieCommie]
    #14879569 - 08/06/11 12:55 AM (12 years, 9 months ago)

Quote:

DieCommie said:
You could put the oxygen in the fuel/explosive material, like a rocket engine.




yeah but im assuming he is using your average hand grenade hahaha but even if that happens what would the explosion cause? it would start deteriorate but since its not under the same pressure as it would be on earth it would be a MUCH BIGGER explosion than what you would expect... all in all until we study more into explosions in outer space dont go throwing random hand grenades out of your space ship! :wink:


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Re: so in theory in space....... [Re: DieCommie]
    #14879596 - 08/06/11 01:06 AM (12 years, 9 months ago)

You could put the oxygen in the fuel/explosive material, like a rocket engine.




and with the way a hand grenade works it would be impossible to do that because the grenade would have to be air tight...so for your idea to work you would have to create a brand new grenade...and then you would make millions!

I copyright this post ;D muahaha now I will have millions and you wont(:<


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Re: so in theory in space....... [Re: GrimReaper6942]
    #14879619 - 08/06/11 01:11 AM (12 years, 9 months ago)

I would guess that grenades already do have the oxygen in the fuel.  :shrug:


Im not sure it would combust fast enough if it didnt.

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Re: so in theory in space....... [Re: DieCommie]
    #14879743 - 08/06/11 02:31 AM (12 years, 9 months ago)

I asked this guy in a pm, and he didn't reply. I was asking if grenades were air tight, I guess the fuse that lights inside the grenade is open after the pin is pulled? I just wasn't sure because I thought in movies you can't see any fuse light in the grenade. obviously those aren't grenades, but I was under the impression it was sealed inside and self oxygenated.


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Re: so in theory in space....... [Re: imachavel]
    #14879745 - 08/06/11 02:34 AM (12 years, 9 months ago)

I dont know... But I dont think it would need to be air tight.  I would presume it uses a solid fuel/oxygen mixture not completely unlike some rockets.

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Re: so in theory in space....... [Re: DieCommie]
    #14879749 - 08/06/11 02:37 AM (12 years, 9 months ago)

Quote:

DieCommie said:
I would guess that grenades already do have the oxygen in the fuel.  :shrug:


Im not sure it would combust fast enough if it didnt.




well speed isn't what I'm thinking of, any explosive can com bust as fast as it wants, look at c4. I think what you mean is if the fuse wasn't sealed but the inside explosive was then how would it get oxygen to com bust?

mainly I'm just thinking that when a fuse is pulled on a grenade, you don't see smoke. therefore the fuse and entire reaction must be self contained, am I wrong? :shrug:


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Re: so in theory in space....... [Re: imachavel]
    #14881779 - 08/06/11 04:37 PM (12 years, 9 months ago)

Grenades are (or at least should be) completely sealed up for the most part.  This prevents them from being rendered inoperable if submerged in water.  The entire process of detonation of a grenade is self-contained.  You could even put the grenade under water, pull the pin, release the spoon, and it would detonate. 

Even old-school cannon fuse will burn under water.


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Re: so in theory in space....... [Re: ChuangTzu]
    #14882155 - 08/06/11 06:11 PM (12 years, 9 months ago)

The US grenades are much simpler than the picture above.  The fuse assembly (M213) contains the striker, striker spring, primer (percussion cap), delay train (chemical delay), and detonator all in line with one another.  The delay train is specified by mil-c-13789a (good luck finding a copy), and is required to burn in an enclosed environment (no access to external oxygen).  Most compositions use potassium nitrate, potassium chlorate, or potassium perchlorate as an oxidizer along with something to consume the oxygen (charcoal) and a binder (dextrin) to regulate burning speed.  The donator is several layers, typically lead styphnate followed by lead azide followed by PETN.  *sigh*  Sometimes, I miss my old job...


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OfflineChuangTzu
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Re: so in theory in space....... [Re: Seuss]
    #14882259 - 08/06/11 06:32 PM (12 years, 9 months ago)

Quote:

Seuss said:
The US grenades are much simpler than the picture above.




Yeah.  On those, the assembly you mention is part of the same mechanism that contains the lever, pin, and everything else except the case and main explosive charge.  It all screws in from the top and there are no other holes in the case.

Quote:

*sigh*  Sometimes, I miss my old job...




I wish that was my job.  I got a demilled Mk.II grenade when I was a kid and spent hours disassembling it and putting it back together again.  If I remember right, there were only 3 or 4 pieces but I was fascinated nonetheless.

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Re: so in theory in space....... [Re: ChuangTzu]
    #14882353 - 08/06/11 06:57 PM (12 years, 9 months ago)

First of all, chemical reactions do not require oxygen to detonate (From what I can remember about fire safety, this is why you can't poor water on a chemical fire to put it out).  Second of all, we can just look at our favorite person of all times, NEWTON.  An object in motion will remain in motion, unless acted upon by another force.  Also, every action has an equal and opposite reaction.  So what ever happened to the grenade, would also happen to the spaceship.  BUT, lets not forget that the spaceship's mass is WAY more than the grenades, hehe, now we are going to have a debate.  Trust me when I say, that both objects would move away from each other at the same rate.


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Re: so in theory in space....... [Re: Jryan]
    #14882366 - 08/06/11 07:00 PM (12 years, 9 months ago)

Quote:

First of all, chemical reactions do not require oxygen to detonate (From what I can remember about fire safety, this is why you can't poor water on a chemical fire to put it out).




Combustion reactions do, and thats what happens in a grenade.

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Re: so in theory in space....... [Re: DieCommie]
    #14882378 - 08/06/11 07:05 PM (12 years, 9 months ago)

Quote:

ChuangTzu said:
Quote:

Seuss said:
The US grenades are much simpler than the picture above.




Yeah.  On those, the assembly you mention is part of the same mechanism that contains the lever, pin, and everything else except the case and main explosive charge.  It all screws in from the top and there are no other holes in the case.

Quote:

*sigh*  Sometimes, I miss my old job...




I wish that was my job.  I got a demilled Mk.II grenade when I was a kid and spent hours disassembling it and putting it back together again.  If I remember right, there were only 3 or 4 pieces but I was fascinated nonetheless.



Quote:

DieCommie said:
Quote:

First of all, chemical reactions do not require oxygen to detonate (From what I can remember about fire safety, this is why you can't poor water on a chemical fire to put it out).




Combustion reactions do, and thats what happens in a grenade.



Ah, are you referring to the fuse then?


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InvisibleDieCommie

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Re: so in theory in space....... [Re: Jryan]
    #14882379 - 08/06/11 07:06 PM (12 years, 9 months ago)

No, Im referring to the final detonation.

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Re: so in theory in space....... [Re: DieCommie]
    #14882388 - 08/06/11 07:08 PM (12 years, 9 months ago)

Quote:

DieCommie said:
No, Im referring to the final detonation.



So maybe it is a "space Granade" ;-0


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OfflineChuangTzu
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Re: so in theory in space....... [Re: Jryan]
    #14882448 - 08/06/11 07:23 PM (12 years, 9 months ago)

If explosives relied on atmospheric oxygen, their burn rate would be severely limited and they wouldn't do much exploding.  That is why every explosive and propellant ever used packs its own oxidizer, whether it's contained with fuel in the same molecule, or separately as a mixture.

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Re: so in theory in space....... [Re: ChuangTzu]
    #14882456 - 08/06/11 07:25 PM (12 years, 9 months ago)

Quote:

ChuangTzu said:
If explosives relied on atmospheric oxygen, their burn rate would be severely limited and they wouldn't do much exploding.  That is why every explosive and propellant ever used packs its own oxidizer, whether it's contained with fuel in the same molecule, or separately as a mixture.



But, if their was any explosion AT all, both objects (Granades matter and Spaceships matter) would move in the opposite directions at the same rate.  Newtonian physics ftw!


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Re: so in theory in space....... [Re: Jryan]
    #14882502 - 08/06/11 07:35 PM (12 years, 9 months ago)

Quote:

Jryan said:
But, if their was any explosion AT all, both objects (Granades matter and Spaceships matter) would move in the opposite directions at the same rate.  Newtonian physics ftw!




Not exactly. 

The grenade's momentum would be conserved, sending shrapnel out radially in such a pattern that the average momentum of the pieces of the grenade is the same as the grenade had before the explosion. 

The momentum of the grenade + spaceship system would remain the same too.  Any particles of the exploding grenade that impinge on the space ship would transfer some momentum to it losing momentum.  The space ship moves off in such a way that the average momentum remains the same. 

The grenade ceases to be an object per se when it blows up and becomes a massive number of particles of various masses and velocities.  The key is that the momentum is conserved, not that the the pieces leave at the same rate.  This would only be the case in certain, particular situations (for example, if the space ship and grenade were loaded into a tube, the grenade's propellant charge was placed between them, and the grenade and space ship had the same mass).

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Re: so in theory in space....... [Re: ChuangTzu]
    #14883712 - 08/07/11 01:03 AM (12 years, 9 months ago)

yes, I understand. I wish grim reaper did he seems to have a hard time understanding. if a grenades fuse wasn't self contained you would see some smoke, no such thing happens.

it is amazing that in space if no force acts upon the explosion, the particles, although scattered, will travel infinitely through space at the same speed until they hit something, minus the shock wave blast, as I believe that needs air to transfer. amazing stuff!


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Re: so in theory in space....... [Re: ChuangTzu]
    #14884984 - 08/07/11 10:53 AM (12 years, 9 months ago)

Quote:

ChuangTzu said:
Quote:

Jryan said:
But, if their was any explosion AT all, both objects (Granades matter and Spaceships matter) would move in the opposite directions at the same rate.  Newtonian physics ftw!




Not exactly. 

The grenade's momentum would be conserved, sending shrapnel out radially in such a pattern that the average momentum of the pieces of the grenade is the same as the grenade had before the explosion. 

The momentum of the grenade + spaceship system would remain the same too.  Any particles of the exploding grenade that impinge on the space ship would transfer some momentum to it losing momentum.  The space ship moves off in such a way that the average momentum remains the same. 

The grenade ceases to be an object per se when it blows up and becomes a massive number of particles of various masses and velocities.  The key is that the momentum is conserved, not that the the pieces leave at the same rate.  This would only be the case in certain, particular situations (for example, if the space ship and grenade were loaded into a tube, the grenade's propellant charge was placed between them, and the grenade and space ship had the same mass).



Good explanation :thumbup:


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Re: so in theory in space....... [Re: Jryan]
    #14886466 - 08/07/11 04:39 PM (12 years, 9 months ago)

yes, of course, momentum is conserved, but that doesn't mean the rules apply COMPLETELY differently just because the objects are in microgravity instead of on earth. if two freight trains slam into each other, will they both because of opposite reaction be pushed backwards in the opposite direction and keep traveling that way? definitely not. this is the difference with objects in space, obviously things don't work exactly the same. but will two freight trains somehow speeding towards each other in a straight line in space, once crashed into each other, both pummel backwards in a perfect direction at the exact same speed they crashed into each other? I think not. the reaction might be different then on earth, but not THAT different, the effect is the same.

now someone said don't even ask why, but that he knew for sure that a grenade exploding right next to the international space station would give both objects equal momentum, the space station, and the grenade shards. I know this isn't true, one thing being the space stations mass is much much greater. but he said this wouldn't matter. surely it would. Now would the space station gain momentum in the opposite direction from the reaction? surely, but it isn't conserved with completely different rules then the ones governing physics on earth. the reaction might be more exaggerated, but the greater mass will mean the space station will only gain so much momentum, as a reaction from the force acted upon it from the grenade.

imho I think it would be pretty impressive all together, just to see the grenade explode next to the international space station, and to see the space station start to move in the opposite direction from the force of the blast. in this example, if the gravity of earth didn't stop the space station, it also, would travel through space in the opposite direction at the same velocity it started moving when the grenade forced it in the opposite direction, for infinity. even slowly, this would be an amazing phenomenon. it's obvious this law holds true, as voyager didn't have it's rockets on towards it's entire trip towards Jupiter, just enough to get it hurtling through space, and then obviously it got momentum and changed trajectory sling shooting off other planets orbits.

the laws of physics in space can be well experienced by playing the game asteroids. the only thing people barely can account for are gravitons. but we know a bigger object with much larger mass and density will very much so attract a smaller object into orbit around it. we've seen it happen in experiments aboard the international space station. salt forms clumps and the smaller clumps will eventually start a slow orbit around the larger clumps after awhile. water itself will form a perfect sphere, showing gravitons are exerted by all objects no matter how small they are. of course this is INSIDE the international space station, where the pressure will keep the water from vaporizing.


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OfflineChuangTzu
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Re: so in theory in space....... [Re: imachavel]
    #14888490 - 08/08/11 01:52 AM (12 years, 9 months ago)

Quote:

imachavel said:
yes, of course, momentum is conserved, but that doesn't mean the rules apply COMPLETELY differently just because the objects are in microgravity instead of on earth. if two freight trains slam into each other, will they both because of opposite reaction be pushed backwards in the opposite direction and keep traveling that way? definitely not. this is the difference with objects in space, obviously things don't work exactly the same. but will two freight trains somehow speeding towards each other in a straight line in space, once crashed into each other, both pummel backwards in a perfect direction at the exact same speed they crashed into each other? I think not. the reaction might be different then on earth, but not THAT different, the effect is the same.




There is no distinction between trains crashing in space or trains crashing on Earth.  A train collision is an inelastic collision because of all the metal that gets fucked up in the process of the crash, which dumps energy to heat.

Quote:


now someone said don't even ask why, but that he knew for sure that a grenade exploding right next to the international space station would give both objects equal momentum, the space station, and the grenade shards. I know this isn't true, one thing being the space stations mass is much much greater. but he said this wouldn't matter. surely it would. Now would the space station gain momentum in the opposite direction from the reaction? surely, but it isn't conserved with completely different rules then the ones governing physics on earth. the reaction might be more exaggerated, but the greater mass will mean the space station will only gain so much momentum, as a reaction from the force acted upon it from the grenade.




Momentum is conserved.  This doesn't mean that it is partitioned equally between the grenade and space station--whether this happens in space or on Earth.  This is because of the different cross sections of reaction of grenade casing and space station with the actual explosion.  Conservation of momentum doesn't require equal momenta for everything involved in the reaction, just that the average momentum of the system remains the same.

Quote:


water itself will form a perfect sphere, showing gravitons are exerted by all objects no matter how small they are.




This is because of the surface tension of water, not because of its gravity.

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Re: so in theory in space....... [Re: ChuangTzu]
    #14899992 - 08/10/11 07:30 AM (12 years, 9 months ago)

no, it'd not, you don't consider that when the expansion stops, it'll gauss out, also, the gasses will cool down and compact.

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Re: so in theory in space....... [Re: myc0nob]
    #14900702 - 08/10/11 11:28 AM (12 years, 9 months ago)

Quote:

myc0nob said:
no, it'd not, you don't consider that when the expansion stops, it'll gauss out, also, the gasses will cool down and compact.




Did you mean to respond to me, or was that for someone else?

Try using the quote function to make it more clear what point you are addressing.

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Re: so in theory in space....... [Re: ChuangTzu]
    #14904989 - 08/11/11 05:52 AM (12 years, 9 months ago)

Quote:

ChuangTzu said:


This is because of the surface tension of water, not because of its gravity.




then why would it form a perfect sphere? the surface tension could hold it together relatively easy without it having to form a perfect sphere, it could be ovoid, or geometrical, and still hold together. it forms a perfectly balanced sphere. and if you leave the water spread out as drops the drops will eventually crash into each other and form a perfect sphere. this is what mercury does on earth. do they really crash or are they attracted to each other? why would you think that gravity only exists on larger scales?

we can only assume there are planets made with a rocky core or a gas core. there are some planets we don't know what is beneath the atmosphere, for all we know there are planets composed entirely of liquid, the gravity would hold itself together as a perfect sphere. I'm sure more experiments can confirm this. take honey for example, it has so much surface tension, even though on earth it will spread all over the place and make a mess, in zero g's it won't move an inch without being acted upon, it has so much surface tension that in space it is the LEAST messiest food, surprisingly. but they spilled some in the air somehow, and two drops clumped together, these two drops did not form a sphere, or if they did it took quite some time. the surface tension will hold liquid together but how it will balance it into a perfect sphere is beyond me :confused:


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Re: so in theory in space....... [Re: imachavel]
    #14905778 - 08/11/11 10:45 AM (12 years, 9 months ago)

Quote:

imachavel said:
then why would it form a perfect sphere?





Because a sphere has the minimum surface area for a given volume of any 3d solid.  The same happens when you blow bubbles.

Quote:

the surface tension could hold it together relatively easy without it having to form a perfect sphere, it could be ovoid, or geometrical, and still hold together.




Because the surface energy of these solids is higher than that of a sphere.

Quote:

and if you leave the water spread out as drops the drops will eventually crash into each other and form a perfect sphere.




I don't think this would be true unless they were the only things in the nearby universe, and over a very long timescale.

Quote:

this is what mercury does on earth.




Is it?

Quote:

do they really crash or are they attracted to each other?




They are slightly attracted to eachother, but this force is very small.

Quote:

why would you think that gravity only exists on larger scales?




Who ever said that?

Quote:


we can only assume there are planets made with a rocky core or a gas core. there are some planets we don't know what is beneath the atmosphere, for all we know there are planets composed entirely of liquid, the gravity would hold itself together as a perfect sphere.




This is true, but on that scale the relative influence of gravity and surface tension are reversed.

Quote:

I'm sure more experiments can confirm this. take honey for example, it has so much surface tension, even though on earth it will spread all over the place and make a mess,




The surface tension of honey must be rather low, not high.  It has high viscosity.

Quote:

in zero g's it won't move an inch without being acted upon, it has so much surface tension that in space it is the LEAST messiest food, surprisingly.




Again, high viscosity, low surface tension (the opposite case of water)

Quote:

but they spilled some in the air somehow, and two drops clumped together, these two drops did not form a sphere, or if they did it took quite some time.




This actually contradicts your claim that it is gravity which drives the water to form spheres.

Quote:


the surface tension will hold liquid together but how it will balance it into a perfect sphere is beyond me :confused:




See my first sentence.

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Re: so in theory in space....... [Re: ChuangTzu]
    #14909326 - 08/12/11 12:11 AM (12 years, 9 months ago)

That is correct, however the closer the grenade is the more shrapnel there is to hit you. However pretty much anything you would come across in space is traveling faster then a bullet or shrapnel.

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OfflineChuangTzu
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Re: so in theory in space....... [Re: sk8ordude]
    #14909343 - 08/12/11 12:16 AM (12 years, 9 months ago)

Quote:

sk8ordude said:
However pretty much anything you would come across in space is traveling faster then a bullet or shrapnel.




Compared to what?

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Re: so in theory in space....... [Re: ChuangTzu]
    #14912101 - 08/12/11 04:13 PM (12 years, 9 months ago)

indeed


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