Three models of Gravity

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cbreiling

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Three models of Gravity
« on: August 20, 2008, 01:33:31 PM »
Warning: this post is Too Long; Don't Read it.  ;)

Everyone here can acknowledge that when you drop a brick, it will accelerate at 9.8 m/s/s towards your big toe, and we can all call that "gravitation" (even if you don't believe in the Force of Gravity). We can also all agree that the greater the mass of the brick, the greater the force impinged upon aforementioned toe on impact.

There are three possible explanations for this phenomena:
  • We are on the inside of a giant wheel (the Halo model) and it is spinning at such an angular velocity to cause we humans who live at its circumference to experience centripetal acceleration, even though technically centrifugal force doesn't exist.
  • We live on the surface of a disk which is accelerating upward at 9.8 m/s/s (the magic elevator model). While we experience grativation, gravity doesn't exist.
  • We are on the surface of a spheroid planet, with a mass and radius such that at our distance from the center, we experience a gravitation acceleration of 9.8 m/s/s (the round earth model)

If you lived inside a house with no windows there's really no way you could tell the difference between these three models. (If your house were small enough, the "magic elevator" could actually be an accelerating rocketship.)

So how could you find out the source of this mysterious downward force called gravitation? By observation, which means you need to get out of that armchair and out of the house.  ;)

1. Halo Model: If you were in the Halo, you'd of course notice this giant thing swooping up into the sky (which would probably look really cool at night). But from a physics standpoint, you could travel the entire length and width of the cylindrical halo, and your gravitational force would remain constant. But there's a limit, for the halo has an edge, and you wouldn't want to fall off.

Plus by observing things not on the halo such as stars and other celestial bodies, you can clearly see your circular movement. All stars would appear to rotate around two points marking the end points of the axis of rotation of your halo.

2. The magic elevator model: (Better known as Flat Earth Theory) Again, we could travel the length and width of the flat earth, and we'd find gravitation to be constant, but there's the limit of not being able to cross the edge (the Ice Wall).

Again, we can observe the motions of heavenly bodies not on our magic elevator. They'd by definition have to accelerate downward at the rate of 9.8 m/s/s, which would make astronomy a little inconvenient. Since we don't see everything accelerating downward away from us, we have to conclude that the entire universe is with us on this magic elevator, which makes for an interesting physics problem.

If the entire universe is accelerating upwards at 9.8 m/s/s then this means that the force of gravitation is the same everywhere, and is aligned downward everywhere. The motions of our solar system's planets pose an especially intractable problem, because there has to be some force holding them "up" just as the ground beneath our feet holds us "up" since we're accelerating upwards.

3. Round Earth Model: (We'll make things complicated by making this Round Earth rotate on an imaginary axis.) If we lived on a round earth, then several things must occur. For one, explorers should be limitless in circumnavigating the planet. The motions of the stars in the night sky must appear to rotate around two imaginary points marking the end points of our earth's axis.

The force of gravitation, attracting us towards the ground, must be explained somehow, since we're not inside a spinning Halo, nor are we on a magic elevator. Therefore we'd have to perform experiments demonstrating that for some unknown reason, things with mass are attracted to one another.
http://en.wikipedia.org/wiki/Cavendish_experiment
http://www.fourmilab.ch/gravitation/foobar/ (do this one in your basement!)

What would be really great would be if we came up with some "law of gravity" we could apply that to the rest of the planets and moons of our solar system. If things with mass are attracted together, then the Earth and Moon would have to have some way of not crashing into each other, and would therefore have to swing around each other, so that each planet's centripetal acceleration perfectly counteracts the force of "gravity" at that distance.

You know, it would be really great if all planets and moons could obey this law. I'm tired of living on this Flat Earth.  ;)
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WardoggKC130FE

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Re: Three models of Gravity
« Reply #1 on: August 20, 2008, 01:35:24 PM »
tl;dr


COME ON?!? You knew that was coming.

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TheEngineer

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Re: Three models of Gravity
« Reply #2 on: August 20, 2008, 02:22:27 PM »
So your number 3 also can't explain observed phenomenon?  Do you have another model for us?


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cbreiling

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Re: Three models of Gravity
« Reply #3 on: August 20, 2008, 02:28:01 PM »
So your number 3 also can't explain observed phenomenon?  Do you have another model for us?

All the observed phenomena in our solar system (I'm leaving out black holes and worm holes and the Tardis) support only one of those three models.
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Re: Three models of Gravity
« Reply #4 on: August 20, 2008, 02:28:29 PM »
Good summary.

Minor nit... depending on the size of the halo, it may be possible to tell that you're in this model inside your house with the windows closed... Coriolis force. But for a large enough halo, this may be hard to detect.

FWIW, it appears to me that FE'ers believe in both 2 and 3. They require 2 for their entire world view, but they also require 3 not only for the Cavendish experiment, but to explain the moons of Jupiter. Can an FE'er verify that I'm right in this assessment?

And here (if I'm right) we come back to Occam's Razor, RE requires just one, while FE requires 2.


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TheEngineer

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Re: Three models of Gravity
« Reply #5 on: August 20, 2008, 02:31:02 PM »
All the observed phenomena in our solar system (I'm leaving out black holes and worm holes and the Tardis) support only one of those three models.
Well, that's good to know.  I guess that means we can rule out number 3.


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Re: Three models of Gravity
« Reply #6 on: August 20, 2008, 02:35:49 PM »
In the second model, I do not understand why the upward movement of the earth has no effect on air particles. And by that I mean why we do not see a constant breeze straight against the ground? As far as I've been led to believe before, air particles were not affected by enough by gravity to be pulled to the ground.

From what I've read on site so far it would seem to me that we would see the impact of the earth against the air as the earth moves upward.

If the air and atmosphere were all held in place by some sort of "dome force" and not affected by the upward movement then wouldn't it hold true that anything inside said dome would also not be affected?


Re: Three models of Gravity
« Reply #7 on: August 20, 2008, 02:39:24 PM »
Engy, stop being a dick.

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TheEngineer

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Re: Three models of Gravity
« Reply #8 on: August 20, 2008, 02:44:12 PM »
I like being a dick.   >:(


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Re: Three models of Gravity
« Reply #9 on: August 20, 2008, 02:44:36 PM »
In the second model, I do not understand why the upward movement of the earth has no effect on air particles. And by that I mean why we do not see a constant breeze straight against the ground? As far as I've been led to believe before, air particles were not affected by enough by gravity to be pulled to the ground.

So... I assume that you're genuinely asking this question and that you also believe Einstein was correct when he said that you can't tell these apart, as the original poster reiterated at the start of this thread. So your question is not that you think a breeze would distinguish these 3 models from each other, but rather that you really don't know.

Well... I'm an RE'er, but the the (other) thing that's preventing a breeze from forming is the ice wall the FE'ers presume exists. If there is no place for the air to go then there will be no breeze. You can see this for yourself (I assume) if you point a pail straight into the wind while hanging out the window of a car. If the pail is deep enough there will be little to no breeze at the bottom because there is no where for the air to go.

Note, the most analgous case in RE is if the earth had a hole in it and the interior were hollow and a vacuum. Then even on earth there would be a breeze as you are stating.


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Re: Three models of Gravity
« Reply #10 on: August 20, 2008, 02:52:34 PM »
In the second model, I do not understand why the upward movement of the earth has no effect on air particles. And by that I mean why we do not see a constant breeze straight against the ground? As far as I've been led to believe before, air particles were not affected by enough by gravity to be pulled to the ground.

So... I assume that you're genuinely asking this question and that you also believe Einstein was correct when he said that you can't tell these apart, as the original poster reiterated at the start of this thread. So your question is not that you think a breeze would distinguish these 3 models from each other, but rather that you really don't know.

Well... I'm an RE'er, but the the (other) thing that's preventing a breeze from forming is the ice wall the FE'ers presume exists. If there is no place for the air to go then there will be no breeze. You can see this for yourself (I assume) if you point a pail straight into the wind while hanging out the window of a car. If the pail is deep enough there will be little to no breeze at the bottom because there is no where for the air to go.

Note, the most analgous case in RE is if the earth had a hole in it and the interior were hollow and a vacuum. Then even on earth there would be a breeze as you are stating.



Your analogy about the pail makes sense but even with it, the pail would experience force pressing against the bottom as would be felt by your hand holding it.

Also, if inside the pail very near the bottom, I tape a small feather to the side. Would I not be able to see the air affect the feather and so in the same way see the affect of the air on trees and even the grass?

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cbreiling

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Re: Three models of Gravity
« Reply #11 on: August 20, 2008, 02:55:54 PM »
In the second model, I do not understand why the upward movement of the earth has no effect on air particles. And by that I mean why we do not see a constant breeze straight against the ground? As far as I've been led to believe before, air particles were not affected by enough by gravity to be pulled to the ground.

Air particles, like everything else with mass, is affected by gravity/gravitation. In our atmosphere, the particles behave as a liquid, so buoyancy keeps some particles up while other particles sink. And air pressure (around 15 psi at sea level) is simply the "weight" of all this air. If you were to take a column of air one square inch in cross section, and as tall as our atmosphere, that column would weigh about 15 pounds.

Quote
From what I've read on site so far it would seem to me that we would see the impact of the earth against the air as the earth moves upward.
As the flat Earth moves upward at 9.8 m/s/s, it is not "pushing against" any outside air, our atmosphere is traveling with us.

Quote
If the air and atmosphere were all held in place by some sort of "dome force" and not affected by the upward movement then wouldn't it hold true that anything inside said dome would also not be affected?

There doesn't need to be a dome, but our atmosphere must be contained at the sides. Air pressure is 15 psi at sea level, so there must be something in the vicinity of the Ice Wall that holds back the air from escaping into space. This barrier must be like a cylinder as tall as our atmosphere is thick (no definite boundary, but many people use the value 62 miles).

So at the Ice Wall there must be a barrier around 62 miles tall, preventing our atmosphere from escaping due to air pressure at altitude.
« Last Edit: August 20, 2008, 02:58:29 PM by cbreiling »
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Re: Three models of Gravity
« Reply #12 on: August 20, 2008, 04:57:49 PM »
As the flat Earth moves upward at 9.8 m/s/s, it is not "pushing against" any outside air, our atmosphere is traveling with us.
If the atmosphere is traveling with us and is not affected by the upward movement of the earth, then why is anything contained in that atmosphere affected? For an example let's say we're in space standing on a giant asteroid/rock/mass. It just so happens that we're standing at the exact "top" of this mass and it also just so happens that the mass is traveling at any given speed in the direction that us standing there would consider straight up. Now supposing we jumped up-we would expend energy and fly upward away from the mass. What force would then cause the energy we created to cease?

I'm not understanding how the same would not hold true here if the air around me is not affected by the only force known to keep things from floating off the ground. If the air around me is not affected by the upward movement then how am I?

Quote
There doesn't need to be a dome, but our atmosphere must be contained at the sides. Air pressure is 15 psi at sea level, so there must be something in the vicinity of the Ice Wall that holds back the air from escaping into space. This barrier must be like a cylinder as tall as our atmosphere is thick (no definite boundary, but many people use the value 62 miles).

So at the Ice Wall there must be a barrier around 62 miles tall, preventing our atmosphere from escaping due to air pressure at altitude.
If there is no "dome" what then keeps the air pressure maintained? I can envision the barrier that you're describing and for my simple mind I think of a cup over even a pail as oldsoldier described traveling upward through space. But with no "top"-that is-nothing to push against why wouldn't it be the same as opening a glass jar full of air in a vacuum?

Re: Three models of Gravity
« Reply #13 on: August 20, 2008, 05:08:45 PM »
The earth is not travelling at a given speed, it is accelerating. You jump up at a given speed which is faster than the earth is travelling at that time, but because the earth is accelerting it catchs up to you. Does that make sense? The principle is the same for the atmosphere.
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Re: Three models of Gravity
« Reply #14 on: August 20, 2008, 05:16:13 PM »
Quote
Your analogy about the pail makes sense but even with it, the pail would experience force pressing against the bottom as would be felt by your hand holding it.

Also, if inside the pail very near the bottom, I tape a small feather to the side. Would I not be able to see the air affect the feather and so in the same way see the affect of the air on trees and even the grass?

Like all analogies, they sometimes leave out various bits in the real world where they break down. The pail explains how wind can be blowing into something and you not feel it. The wind force pushing against my hand... kinda breaks down the analogy. Also I'm not going to debate the feather issue... I'm sure there will be some leakage of air so it may move. But yea... if I understand it correctly, if there were a hot and cold zone in the pail, the air should circulate internally as you'd expect, almost independend of the car's speed.

I am merely maintaining that you need 2 things to be able to feel wind (or any sort of fluid flow) one is some motive force and the other is some place for the flowing stuff to go to. In both RE and FE the motive force are the same in that they're indistinguishable from each other. "Gravity" or acceleration. Regarding the some place to go, FE has that ice wall. RE has a more elegant sphere. So... no wind.

Ok... let's try another analogy. Let's assume you're in an elevator with a glass of water and something floating inside it. The elevator can be on the earth, but once it starts moving it maintains a constant accceleration, let's call it "g". Start up the elevator. You're now feeling a 2g force (combined). Did the floater in the glass move? Did you feel a breeze once the elevator started?

yea, you may have gotten weak in the knees, but that's your strength, not any wind pushing you down. Air pressure may change as now the air "weighs" twice as much, but that happens immediately and quickly reaches a steady state. So after that possible(?) initial burst... no wind.

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Re: Three models of Gravity
« Reply #15 on: August 20, 2008, 06:04:35 PM »
The earth is not travelling at a given speed, it is accelerating. You jump up at a given speed which is faster than the earth is travelling at that time, but because the earth is accelerting it catchs up to you. Does that make sense? The principle is the same for the atmosphere.
It does and it doesn't :)

If I accept that the earth is accelerating and that is the reason objects "fall" then I question again why a stationary air particle (or in this case multiple particles) are not impacted by the earth in the same way.

The atmosphere would have to be accelerating at the same rate as the earth in order for us not to be able to "see" the effect wouldn't it?

Re: Three models of Gravity
« Reply #16 on: August 20, 2008, 06:09:46 PM »
The earth is not travelling at a given speed, it is accelerating. You jump up at a given speed which is faster than the earth is travelling at that time, but because the earth is accelerting it catchs up to you. Does that make sense? The principle is the same for the atmosphere.
It does and it doesn't :)

If I accept that the earth is accelerating and that is the reason objects "fall" then I question again why a stationary air particle (or in this case multiple particles) are not impacted by the earth in the same way.

The atmosphere would have to be accelerating at the same rate as the earth in order for us not to be able to "see" the effect wouldn't it?

What makes you think "gravity" works differently in this case? Wouldn't your logic apply if you replace FE's acceleration with RE's gravity?

The reason why an "air particle" doesn't hit the ground is because of the other air particles underneath it.


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Parsifal

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Re: Three models of Gravity
« Reply #17 on: August 20, 2008, 06:11:30 PM »
It does and it doesn't :)

If I accept that the earth is accelerating and that is the reason objects "fall" then I question again why a stationary air particle (or in this case multiple particles) are not impacted by the earth in the same way.

The atmosphere would have to be accelerating at the same rate as the earth in order for us not to be able to "see" the effect wouldn't it?

The Earth applies a force to the atmoplane, which (by Newton's third law of motion) applies an equal and opposite force to the Earth. This force causes the air to compress, causing the force between them to increase until the force being applied to the atmoplane is enough to accelerate it at 9.8 m s-2. This equilibrium occurs when the air reaches standard atmospheric temperature and pressure. Then the atmoplane accelerates at the same rate as the Earth.
I'm going to side with the white supremacists.

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Re: Three models of Gravity
« Reply #18 on: August 20, 2008, 06:12:10 PM »
Ok... let's try another analogy. Let's assume you're in an elevator with a glass of water and something floating inside it. The elevator can be on the earth, but once it starts moving it maintains a constant accceleration, let's call it "g". Start up the elevator. You're now feeling a 2g force (combined). Did the floater in the glass move? Did you feel a breeze once the elevator started?

yea, you may have gotten weak in the knees, but that's your strength, not any wind pushing you down. Air pressure may change as now the air "weighs" twice as much, but that happens immediately and quickly reaches a steady state. So after that possible(?) initial burst... no wind.
Ahh.. but take the "roof" off the same elevator and you will feel the air "blowing" against you as you rise wouldn't you?

I honestly don't know what the floater would do :P I don't have the scientific knowledge that a lot of you on this site display.

But I enjoy the discussion thoroughly. Gets my brain going.

Re: Three models of Gravity
« Reply #19 on: August 20, 2008, 06:18:45 PM »
Ok... let's try another analogy. Let's assume you're in an elevator with a glass of water and something floating inside it. The elevator can be on the earth, but once it starts moving it maintains a constant accceleration, let's call it "g". Start up the elevator. You're now feeling a 2g force (combined). Did the floater in the glass move? Did you feel a breeze once the elevator started?
Ahh.. but take the "roof" off the same elevator and you will feel the air "blowing" against you as you rise wouldn't you?

Not if the roof is high enough... that's where the pail analogy helped.


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Re: Three models of Gravity
« Reply #20 on: August 20, 2008, 06:21:07 PM »
What makes you think "gravity" works differently in this case? Wouldn't your logic apply if you replace FE's acceleration with RE's gravity?

The reason why an "air particle" doesn't hit the ground is because of the other air particles underneath it.

I've always thought that air particles didn't have enough "weight" for RE gravity to affect them as much. That would explaint why air is "thicker" at sea level and gets "thinner" at higher altitude.

I guess I see RE's gravity as a pulling force that does not affect all things equally. But when I try and envision an upward accellerating mass, I can only imagine it's effect to be constant.

Re: Three models of Gravity
« Reply #21 on: August 20, 2008, 06:30:09 PM »
What makes you think "gravity" works differently in this case? Wouldn't your logic apply if you replace FE's acceleration with RE's gravity?

The reason why an "air particle" doesn't hit the ground is because of the other air particles underneath it.

I've always thought that air particles didn't have enough "weight" for RE gravity to affect them as much. That would explaint why air is "thicker" at sea level and gets "thinner" at higher altitude.

I guess I see RE's gravity as a pulling force that does not affect all things equally. But when I try and envision an upward accellerating mass, I can only imagine it's effect to be constant.

Ahh... yea... well... your intuition is wrong. Hard to adjust, I can appreciate that. Did you hear of the story of Galileo droping a heavy ball and a light ball off of the leaning tower of piza (apocryphal I know) or about the astronaut who dropped a feather and a ball on the moon?

Similarly, if I drop an "air particle" on the moon, it will fall to the ground.

On the off chance that you did have some physics but forgot... the force is less on the air particle, but then so is its mass. They "just happen" to cancel each other out so everything is accelerated at 9.8m/s/s.

The "just happen" bit is a whole 'nuther story.

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Re: Three models of Gravity
« Reply #22 on: August 20, 2008, 06:34:58 PM »
The Earth applies a force to the atmoplane, which (by Newton's third law of motion) applies an equal and opposite force to the Earth. This force causes the air to compress, causing the force between them to increase until the force being applied to the atmoplane is enough to accelerate it at 9.8 m s-2. This equilibrium occurs when the air reaches standard atmospheric temperature and pressure. Then the atmoplane accelerates at the same rate as the Earth.

So then the atmosphere is is like a bubble on top of a solid surface. And the air around us is pressurized and is not impacted by the upward accelerating earth. Why then would any object be caught up to by the earth?

Maybe I'm confusing myself ???  Without RE gravity, do we even have weight? If there is no "downward" force being applied to us and the reason an object seems to fall is only because it is no longer traveling faster than the earth, what then causes an object to want to go to the ground when held in one's hand?

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Re: Three models of Gravity
« Reply #23 on: August 20, 2008, 06:39:22 PM »
So then the atmosphere is is like a bubble on top of a solid surface. And the air around us is pressurized and is not impacted by the upward accelerating earth. Why then would any object be caught up to by the earth?

On the contrary, the air is accelerated by the Earth. This equilibrium is enabled by the fact that the air is pressurised, and so the force that causes the air to accelerate at 9.8 m s-2 can be applied in the opposite direction to the Earth. If the air did not exert any pressure on the Earth at its current density, it could not be accelerated by the Earth because of Newton's third law of motion, and would simply compress into an infinitely dense and infinitesimally thin layer on the surface.

Maybe I'm confusing myself ???  Without RE gravity, do we even have weight? If there is no "downward" force being applied to us and the reason an object seems to fall is only because it is no longer traveling faster than the earth, what then causes an object to want to go to the ground when held in one's hand?

Weight is a fictitious force in the same way that centrifugal force doesn't really exist. The reason an object in your hand feels as though there is a downward force on it is because you are accelerating up with the Earth, and the object is resisting this acceleration.
« Last Edit: August 20, 2008, 06:41:14 PM by Robosteve »
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Re: Three models of Gravity
« Reply #24 on: August 20, 2008, 06:41:27 PM »
What makes you think "gravity" works differently in this case? Wouldn't your logic apply if you replace FE's acceleration with RE's gravity?

The reason why an "air particle" doesn't hit the ground is because of the other air particles underneath it.

I've always thought that air particles didn't have enough "weight" for RE gravity to affect them as much. That would explaint why air is "thicker" at sea level and gets "thinner" at higher altitude.

Hmmmm.... this is a really good question... specifically... does the ice wall theory in FE imply that the atmosphere is of constant density up until you're at an altitude above the ice wall?

Similarly, to get back to the OP... does the Halo model have the same thing? The side-walls of the halo... they clearly keep the atmosphere in, so in the halo model, at just above the height of the wall... is there a sudden jump to vacuum?

In other words, how does FE explain lower pressure at altitude?

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Re: Three models of Gravity
« Reply #25 on: August 20, 2008, 06:44:19 PM »
In other words, how does FE explain lower pressure at altitude?

The mass of air above a point ten kilometres above the ground is less than the mass of air above the surface. It requires less force to accelerate it at 9.8 m s-2, and therefore must be at a lower pressure to satisfy Newton's third law of motion.
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Re: Three models of Gravity
« Reply #26 on: August 20, 2008, 06:45:25 PM »

Ahh... yea... well... your intuition is wrong. Hard to adjust, I can appreciate that. Did you hear of the story of Galileo droping a heavy ball and a light ball off of the leaning tower of piza (apocryphal I know) or about the astronaut who dropped a feather and a ball on the moon?

Similarly, if I drop an "air particle" on the moon, it will fall to the ground.

On the off chance that you did have some physics but forgot... the force is less on the air particle, but then so is its mass. They "just happen" to cancel each other out so everything is accelerated at 9.8m/s/s.

The "just happen" bit is a whole 'nuther story.

;D I was trying to keep from using any "off earth" references seeing as that many on this site don't believe that space travel has happened so the knowledge would be unproven.

And I'm sorry to say-no physics here. Not even the basics :-\  I was not a good student back in the day (maybe would have graduated last in my class if I had even graduated) and during my college career when I was a good student I never took physics and remeber very little even from my other science courses in the way of physics. I am less than a layman.

Re: Three models of Gravity
« Reply #27 on: August 20, 2008, 06:47:20 PM »
If I accept that the earth is accelerating and that is the reason objects "fall" then I question again why a stationary air particle (or in this case multiple particles) are not impacted by the earth in the same way.

The atmosphere would have to be accelerating at the same rate as the earth in order for us not to be able to "see" the effect wouldn't it?
That is correct.
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Re: Three models of Gravity
« Reply #28 on: August 20, 2008, 06:54:14 PM »
The mass of air above a point ten kilometres above the ground is less than the mass of air above the surface.
And why is that?
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Re: Three models of Gravity
« Reply #29 on: August 20, 2008, 06:55:07 PM »
In other words, how does FE explain lower pressure at altitude?

The mass of air above a point ten kilometres above the ground is less than the mass of air above the surface. It requires less force to accelerate it at 9.8 m s-2, and therefore must be at a lower pressure to satisfy Newton's third law of motion.

Ok... I guess I'll concede 1/2 of this point. The "weight" of the air above will compress the air below. But here's where we're likely to differ... the ice wall just happens to be exactly the right height for this to happen? If it were higher we could trap more air and our air pressure would be higher than it is. If it were lower, the reverse. So... either the ice wall is coincidentally just the right height or ... someone can calculate how high it needs to be in order to give us the observed air pressure.

How high are the ice walls again?