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nakors_junk_bag
Lobster Bisque


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The Earth and centrifugal force?
#5034979 - 12/08/05 04:50 PM (18 years, 5 months ago) |
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It occurred to me, maybe erroneously that as we sail through space on our orbit is it possible that eight pounds of lead will gain and lose wieght at different times in orbit because of the force created as we sail through space?
Can someone please help me with this, I am losing sleep.
-------------------- Asshole
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manbeef
psychedelicfarmer


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Yep. That is correct. Also, you will weigh a few pounds less if you were on the equator as opposed to being at the north or south poles.
This does not mean the fat magically melts off of your ass, your mass will still be the same, it just means that gravity is weaker on the equator as opposed to the poles.
Weight is relative to how strong the gravity field you are in is.
Mass is the relationship between the density of an object and the volume it occupies.
Hopefully that helps you out a bit!
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nakors_junk_bag
Lobster Bisque


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Re: The Earth and centrifugal force? [Re: manbeef]
#5035061 - 12/08/05 05:10 PM (18 years, 5 months ago) |
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good me and a friend a mine were arguing about this and he didn't believe me.
anyone who cares to dispute this please do!!!
-------------------- Asshole
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trendal
J♠


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Loc: Ontario, Canada
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Re: The Earth and centrifugal force? [Re: manbeef]
#5035138 - 12/08/05 05:25 PM (18 years, 5 months ago) |
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Quote:
manbeef said: Yep. That is correct. Also, you will weigh a few pounds less if you were on the equator as opposed to being at the north or south poles.
This does not mean the fat magically melts off of your ass, your mass will still be the same, it just means that gravity is weaker on the equator as opposed to the poles.
Your reasoning here is a little suspect...
Yes, the gravitational field at ground level on the equator is slightly less than it is at the poles...but this isn't due to centripedal force or anything like that. The Earth bulges around the equator, so when you stand at "ground level" on the equator you are actually farther from the Earth's center than if you were standing on one of the poles. Gravity is inversely proportional to distance from the center, so the force you experience at the equator is SLIGHTLY different than at the poles.
This will not create a difference of a few pounds, though. The distances involved just aren't great enough. I suspect it ammounts to a few grams difference.
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Once, men turned their thinking over to machines in the hope that this would set them free. But that only permitted other men with machines to enslave them.
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nakors_junk_bag
Lobster Bisque


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Re: The Earth and centrifugal force? [Re: trendal]
#5035171 - 12/08/05 05:30 PM (18 years, 5 months ago) |
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see this is good, I would still like to know if my theory has any verity in it. I also understand we are talking extremely small differences in weight. Trendal do you think I could be right?
-------------------- Asshole
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manbeef
psychedelicfarmer


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Re: The Earth and centrifugal force? [Re: trendal]
#5035217 - 12/08/05 05:41 PM (18 years, 5 months ago) |
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Yes the earth does bulge out around the equator, making the radius larger and therefore less gravity, but that alone won't amount to a difference of a couple pounds.
Centripetal force acts perpendicular to an object's spin axis and is based upon the distance from this spin axis. At the north pole, the distance to the spin axis would be 0, so there is no centripetal force, only gravity.
However, at the equator, gravity is perpendicular to the spin axis. Centripetal force is also perpendicular to the spin axis. Gravity acts towards the centre of the earth, and centripetal force acts in the opposite direction. Add those two vectors together, and the net gravitational force is still towards the centre of the earth, but it is less than the gravity force.
And yes this actually amounts to a difference of 2 pounds for a person's weight.
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trendal
J♠


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Re: The Earth and centrifugal force? [Re: manbeef]
#5035420 - 12/08/05 06:18 PM (18 years, 5 months ago) |
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Actually the centripetal force acts inwards - towards the center of the earth. "centri-petal" literally means "center-seeking".
The reactionary force, "centrifugal", is what is felt as an outward force...but it isn't actually a "force", just a reaction to one.
As for the "2 pounds"....that isn't always true - it depends on the mass of the object in question. For myself (at 55kg) the change is almost 1kg between the pole and the equator due to the centripetal force. This scales up or down proportionally to the mass of the object (so that someone at 100kg will experience a difference of over 1.6kg).
The effect of the weakened gravity is probably only a few grams at most, which is what I was getting at in my last post.
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Once, men turned their thinking over to machines in the hope that this would set them free. But that only permitted other men with machines to enslave them.
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ChuangTzu
starvingphysicist



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I interpreted this question as relating to the orbit of the earth as a whole, for an object stationary on the Earth's surface.
In that case, the radius of Earth's orbit is about 150 million km with a deviation of 5 million km. The diameter of the Earth is much smaller than this so it can be neglected. The Earth moves around the sun at 110,000km/h = 31,000m/s. Centrifugal force is proportional to v^2/r so, if the Earth moved at a constant speed, the difference in apparant weights at the innermost and outermost positions of the Earth in its orbit would be noticable (on the order of 10ths of a gram for a 1kg object, feel free to check this for me).
However, the Earth moves faster when it is closer to the sun and slower when it is farther away, perfectly balancing the two contributions to centrifugal force.
There is still the combined effects of the Earth's rotation and diameter to consider though---the outer edge of the Earth is spinning in the same direction as the Earth is travelling in space and the inner edge is travelling "backwards" (with respect to the whole Earth's motion). The effect of this velocity difference adds to the effect from the difference in radius. I'm too lazy to calculate the total weight variation but I suspect it is very, very small. That doesn't mean it doesn't exist, just that variations due to vibrations in the floor and electrical disturbances are likely to be much higher.
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nakors_junk_bag
Lobster Bisque


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Re: The Earth and centrifugal force? [Re: ChuangTzu]
#5041106 - 12/09/05 07:43 PM (18 years, 5 months ago) |
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So, as we travel along on or orbit we do gain and lose small degrees of weight. I thought so. Depending on where you are when the earth reaches its elliptical apex then you either way more or less right? I thought so. Yall have been very helpful. Grazzi
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ThePredator
Your a eunich ifyou don't useunix!

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The ammount different is negligable. Anyways your poundage or gramage won't change because that is mass, your Newtons will change though.
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nakors_junk_bag
Lobster Bisque


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Re: The Earth and centrifugal force? [Re: ThePredator]
#5041259 - 12/09/05 08:37 PM (18 years, 5 months ago) |
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Mass and weight aren't necessarily the same thing, in space my mass is consistent with my mass on earth however my weight certainly changes. Weight is invariably tied to gavity, mass is tied to nothing, it just is.
-------------------- Asshole
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Gijith
Daisy Chain Eater

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Here's an equation I use on occasion. It gives theoretical gravity (gt) as a funtion of latitude (phi). It takes into account the centripetal force, the distance of radius and the distance from the heavier mass of the core.
(gt) = (g0)*(1+0.005278895*sin^2(phi)+0.000023462*sin^4(phi))
where (g0) is theoretical gravity at the equator
In the end, there's a difference of about 5,000 mGals between the poles and the equator (stronger at the poles).
-------------------- what's with neocons and the word 'ilk'?
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ThePredator
Your a eunich ifyou don't useunix!

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I never said they were the same I said they were different, everybody in the thread was talking about kilograms which is not weight, it is mass.
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DieCommie

Registered: 12/11/03
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Re: The Earth and centrifugal force? [Re: ThePredator]
#5041633 - 12/09/05 10:15 PM (18 years, 5 months ago) |
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Quote:
ThePredator said:...everybody in the thread was talking about kilograms which is not weight, it is mass.
I dont see anybody talking about kilograms.
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ThePredator
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Re: The Earth and centrifugal force? [Re: trendal]
#5041673 - 12/09/05 10:23 PM (18 years, 5 months ago) |
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Quote:
trendal said: Actually the centripetal force acts inwards - towards the center of the earth. "centri-petal" literally means "center-seeking".
The reactionary force, "centrifugal", is what is felt as an outward force...but it isn't actually a "force", just a reaction to one.
As for the "2 pounds"....that isn't always true - it depends on the mass of the object in question. For myself (at 55kg) the change is almost 1kg between the pole and the equator due to the centripetal force. This scales up or down proportionally to the mass of the object (so that someone at 100kg will experience a difference of over 1.6kg).
The effect of the weakened gravity is probably only a few grams at most, which is what I was getting at in my last post.
I do :/
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ChuangTzu
starvingphysicist



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Quote:
nakors_junk_bag said: So, as we travel along on or orbit we do gain and lose small degrees of weight. I thought so. Depending on where you are when the earth reaches its elliptical apex then you either way more or less right?
No. The centrifugal force felt by objects on the Earth is the same at all points on its orbit. The only differences in weight are due to the relative motion of the opposite sides of the Earth (between light and dark sides), but your digi scale will never see this.
ThePredator: You're right that none of this affects mass, but the way most of us measure mass on Earth is by measuring weight. The scale shows kilograms, so that's what we'll see a deviation in. Of course, it's actually a force that is varying and that's why everyone is referring to weight and centrifugal "force". You're right, but you're nitpicking.
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nakors_junk_bag
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Re: The Earth and centrifugal force? [Re: ChuangTzu]
#5042843 - 12/10/05 03:07 AM (18 years, 5 months ago) |
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How is it possible that the centrifugal force is the same on all points of an elliptical orbit? It seems to me that when the earth reaches the apexes on its orbit and goes from speeding outward to inward that there must be some change in the force created by the movement both inward and outward depending on whether you exist in the darkened side or the side that has been bathed in light. Also as the earth itself spins on its own axis those who are caught at the moment before the inward movement starts(the ones who have achieved maximum distance from the sun ) should theoretically have achieved less weight by simple definition and understanding of terms, by mere degrees, however small. the sun exerts a gravitational pull on the earth, else we would speed off into the abyss, doesn't this also mean the same laws apply to the dynamics between it and the earth and earth and us or even the moon. Is it also not common knowledge that we every year venture further form the sun in orbit due to momentum? Is not momentum relative to distance from sun the result of the force of speed around a circle times the weight of our planet?
Provided that it is, then would it not be safe to say that even as the earth shuns the pull of the sun due to its involuntary orbit to the sun, would it not be the same case for man and its involuntary spin around both the earth and the sun at a larger extent?
I have simply seen no empirical evidence providing proof either way.
-------------------- Asshole
Edited by nakors_junk_bag (12/10/05 03:18 AM)
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nakors_junk_bag
Lobster Bisque


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By the weigh, kilograms are units of weight measurement, whoever said there was a difference. they eqaul a thousand grams. a thousand grams being a mere 3 tenths of and ounce away from 36 onunces.
-------------------- Asshole
Edited by nakors_junk_bag (12/10/05 02:12 PM)
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ThePredator
Your a eunich ifyou don't useunix!

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Nay, kilograms are a measurement of mass the only weight measurement I know of is newtons. http://dictionary.reference.com/search?q=kilograms
And when it comes to science you can never be too nitpicky.
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ChuangTzu
starvingphysicist



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Like I said before, there are two contributions to the centrifugal force that are varying here---velocity and radius. The earth doesn't move at a constant speed in its orbit, it moves faster at the inner radii and slows down as it gets farther from the sun. This is due to the fact that the earth has a fixed total energy, kinetic + potential. All this was figured out by Kepler way back in the day.
If I had time I could work out a proof, but since I don't I can only outline how you can do it yourself if you're so inclined: [1]Write out the equation of motion of the Earth around the sun in cartesian coordinates (you'll have to get the parameters from a piece of reference material).
[2]Take the first (vector) derivative of position with respect to time v = dr(t)/dt
[3]Write the equation for centrifugal force, mv(t)^2/r(t) [radially]
[4]Plug v and r into the equation in 3) and you should find that the resulting function F is not dependant on t, i.e. it is a constant at all points on the Earth's orbit.
Quote:
doesn't this also mean the same laws apply to the dynamics between it and the earth and earth and us or even the moon. Is it also not common knowledge that we every year venture further form the sun in orbit due to momentum? Is not momentum relative to distance from sun the result of the force of speed around a circle times the weight of our planet?
Hey now, if you throw the moon into the mix all bets are off. Of course the moon exerts a huge influence on objects on the Earth. A measurement of weight made when the moon is overhead will certainly be different from one made when the moon is 90 degrees out of phase from that position. Then there are the effects from the other planets in the solar system, and the other stars in the galaxy, the other galaxies, etc.
If your original question was about whether the weight of an object stationary on the Earth's surface varies with time, the answer is yes. If you're trying to relate it to the orbit of the Earth, the answer is no.
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s it also not common knowledge that we every year venture further form the sun in orbit due to momentum?
If we're moving further away from the sun each year, this is the first I've heard of it. If anything, we should be spiraling slowly inward.
Quote:
And when it comes to science you can never be too nitpicky.
Yes you can, when the nitpicking gets in the way of the discussion.
Edited by ChuangTzu (12/10/05 09:53 AM)
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Seuss
Error: divide byzero


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Re: The Earth and centrifugal force? [Re: ChuangTzu]
#5051180 - 12/12/05 04:34 AM (18 years, 5 months ago) |
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>> And when it comes to science you can never be too nitpicky. > Yes you can, when the nitpicking gets in the way of the discussion.
In the famous words of my a-bomb (modern physics) prof... "imagine that we have a spherical chicken moving with a velocity of ...."
-------------------- Just another spore in the wind.
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ChuangTzu
starvingphysicist



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Re: The Earth and centrifugal force? [Re: Seuss]
#5051370 - 12/12/05 07:41 AM (18 years, 5 months ago) |
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Hehe 
Reminds me of the joke one of my physics prof.s told us:
Quote:
Some crazy gambler kidnaps a biologist, a chemist, and a physicist and locks them in a dungeon or somewhere and tells them each that they'll be let out when they have devised a method to win a horse bet every time. So, they set to work in their respective dungeon labs...
After some months, the biologist completed his work. --"So, what have you come up with?" the gambler asked, to which the he biologist responded by proudly showing off a new breed of horse he had genetically engineered to run twice as fast as a normal horse (and grow about 5x as fast apparently). The gambler thanked him and let him go.
After another few months, the chemist finished his work. --"So, what have you come up with?" the gambler asked, to which the chemist responded by demonstrating a new drug which could be injected into a horse just before a race, which gave the horse a boost in energy for the duration of the race, and broke down quickly to untraceable metabolites soon after. The gambler thanked him and let him go.
Not long after, the physicist finished his work. "Well, what did you come up with?" the gambler asked, to which the physicist responded, "Assume spherical horses running in a vacuum..."
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