|
Doc_T
Random Dude




Registered: 03/06/09
Posts: 42,395
Loc: Colorado
|
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.)
-------------------- You make it all possible. Doesn't it feel good?
|
DieCommie

Registered: 12/11/03
Posts: 29,258
|
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.
|
Doc_T
Random Dude




Registered: 03/06/09
Posts: 42,395
Loc: Colorado
|
Re: so in theory in space....... [Re: DieCommie]
#14828946 - 07/26/11 06:03 PM (12 years, 9 months ago) |
|
|
Space is weird, physics is weird.
-------------------- You make it all possible. Doesn't it feel good?
|
DieCommie

Registered: 12/11/03
Posts: 29,258
|
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.
|
Stonehenge
Alt Center

Registered: 06/20/04
Posts: 14,850
Loc: S.E.
|
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?
-------------------- “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) Trade list http://www.shroomery.org/forums/showflat.php/Number/18047755
|
DieCommie

Registered: 12/11/03
Posts: 29,258
|
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) .
|
johnm214


Registered: 05/31/07
Posts: 17,582
Loc: Americas
|
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.
|
Doc_T
Random Dude




Registered: 03/06/09
Posts: 42,395
Loc: Colorado
|
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?
-------------------- You make it all possible. Doesn't it feel good?
|
Linus
Chief Bromden



Registered: 06/21/09
Posts: 855
Loc: Cripple Creek
Last seen: 10 years, 4 months
|
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?
-------------------- I've done a lot of drugs in the past, I still do. Abracadabra
|
johnm214


Registered: 05/31/07
Posts: 17,582
Loc: Americas
|
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.
|
DieCommie

Registered: 12/11/03
Posts: 29,258
|
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)
|
johnm214


Registered: 05/31/07
Posts: 17,582
Loc: Americas
|
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.
|
DieCommie

Registered: 12/11/03
Posts: 29,258
|
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.
|
imachavel
I loved and lost but I loved-ftw



Registered: 06/06/07
Posts: 31,564
Loc: You get banned for saying that
Last seen: 12 hours, 22 minutes
|
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
--------------------
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!
I'm never giving you the password again. Jerk
|
Doc_T
Random Dude




Registered: 03/06/09
Posts: 42,395
Loc: Colorado
|
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.
-------------------- You make it all possible. Doesn't it feel good?
|
imachavel
I loved and lost but I loved-ftw



Registered: 06/06/07
Posts: 31,564
Loc: You get banned for saying that
Last seen: 12 hours, 22 minutes
|
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.
--------------------
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!
I'm never giving you the password again. Jerk
|
imachavel
I loved and lost but I loved-ftw



Registered: 06/06/07
Posts: 31,564
Loc: You get banned for saying that
Last seen: 12 hours, 22 minutes
|
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
--------------------
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!
I'm never giving you the password again. Jerk
|
Doc_T
Random Dude




Registered: 03/06/09
Posts: 42,395
Loc: Colorado
|
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.
-------------------- You make it all possible. Doesn't it feel good?
|
imachavel
I loved and lost but I loved-ftw



Registered: 06/06/07
Posts: 31,564
Loc: You get banned for saying that
Last seen: 12 hours, 22 minutes
|
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.
--------------------
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!
I'm never giving you the password again. Jerk
|
imachavel
I loved and lost but I loved-ftw



Registered: 06/06/07
Posts: 31,564
Loc: You get banned for saying that
Last seen: 12 hours, 22 minutes
|
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??
--------------------
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!
I'm never giving you the password again. Jerk
|
|