Freefall

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Freefall
« on: March 09, 2007, 10:50:20 PM »
What is the explanation of your stomach rising within your chest (an easily experienced feeling) when you are in freefall?  This wouldn't happen if the earth were accelerating up to meet you.  Rather, it would only occur if you yourself were accelerating down towards the earth.

The equivalence principle works for when you're on the surface, but when you leave that surface and are still feeling the acceleration, you can conclude that it's not due to that surface literally accelerating "up" toward you.
« Last Edit: March 09, 2007, 10:52:58 PM by The Philosopher »

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unclegravy

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Re: Freefall
« Reply #1 on: March 09, 2007, 10:55:18 PM »
You're a genius.
I never thought about that.
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TheEngineer

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Re: Freefall
« Reply #2 on: March 09, 2007, 11:16:46 PM »
What causes this sensation with gravity?


BTW, the Equivalence Principle holds for all points in space.


"I haven't been wrong since 1961, when I thought I made a mistake."
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Re: Freefall
« Reply #3 on: March 09, 2007, 11:34:44 PM »
What causes this sensation with gravity?


BTW, the Equivalence Principle holds for all points in space.
From http://www1.jsc.nasa.gov/er/seh/cell_growth_in_zero_g.pdf
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The tendency to move in a straight line is inertia. Stresses are felt inside your body as its parts push on one another to allow them to accelerate at the same rate. Your interpretation of those stresses is a weight-like feeling in the direction opposite your acceleration.

Also from here http://www.time.com/time/magazine/article/0,9171,824452,00.html?promoid=googlep
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Weightlessness is easy to achieve on earth, but only for short intervals. The simplest way is to jump off something, even a chair. While the jumper is in free fall, his body as a whole is pulled by the earth's gravitation, but the parts of his body feel weightless. In the same way a person in a rapidly descending elevator feels his stomach rise. Actually it does rise: the elevator's fall has made the stomach lose weight, and the elastic tissues that support it have pulled it upward. When the elevator stops descending, gravity resumes control. The stomach regains its weight and settles back into place.

Also from the above article, how is this explained?
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A better system is to fly an airplane over a curved course in a part of a gentle outside loop. If the speed and sharpness of the curve are correct, centrifugal force exactly balances the earth's gravitation. Everything in the airplane, including the pilot, suddenly becomes weightless.
You're a pilot, you should try this yourself. 

In the air above the accelerating flat earth you should not feel any force within yourself, because there's no force acting on you once you leave the surface.  This is what I meant by the equivalence principle not holding true (not that it didn't work in some circumstances, just that it didn't apply when above the surface).  Though the gravitation experienced on the surface is equivalent to that of gravity on the surface, once you leave the surface, the acceleration from the FE model would no longer affect you, and yet it's easily experienced that it does.  By 'looking out our window', so to speak, we are able to differentiate between the different types of acceleration (whether caused by a gravitational field, or uniform directional acceleration of a 'plane' of sorts).
« Last Edit: March 09, 2007, 11:39:45 PM by The Philosopher »

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TheEngineer

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Re: Freefall
« Reply #4 on: March 10, 2007, 12:31:19 AM »
The Equivalence Principle holds everywhere.  Tell me, what force do you feel on your body when you are in freefall?


"I haven't been wrong since 1961, when I thought I made a mistake."
        -- Bob Hudson

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themateoflink

Re: Freefall
« Reply #5 on: March 10, 2007, 03:40:17 AM »
What is the explanation of your stomach rising within your chest (an easily experienced feeling) when you are in freefall?  This wouldn't happen if the earth were accelerating up to meet you.  Rather, it would only occur if you yourself were accelerating down towards the earth.

This is the force you feel on your body when you are in freefall.

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TheEngineer

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Re: Freefall
« Reply #6 on: March 10, 2007, 06:53:39 AM »
Sorry, but I don't recognize that force.  Be more specific.


"I haven't been wrong since 1961, when I thought I made a mistake."
        -- Bob Hudson

Re: Freefall
« Reply #7 on: March 10, 2007, 08:29:08 AM »
Sorry, but I don't recognize that force.  Be more specific.

Stop avoiding the question just because there's no answer based on the FE model... I explained it with those quotes above, and they're VERY specific.  When you accelerate down there's a reaction force within you, due to your body's inertia, that causes your stomach to rise within your chest.

When above the surface in the FE model, there should be no force acting on you.  Rather, the earth would accelerate up to meet you.  In FE, you would not feel any forces acting on you when you're in the middle of the air, supposedly with no forces acting upon you.

In the RE model, this is caused by gravity.  On the surface, the experiences of gravity and acceleration are the same, but when you leave the surface you should not feel the effects of UA, but you would feel the effects of gravity.

Einstein never said gravity was just an illusion; he said that the experiences of being accelerated due to gravity and just being accelerated are identical, just from different frames of reference.

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EnragedPenguin

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Re: Freefall
« Reply #8 on: March 10, 2007, 10:32:50 AM »
An astronaut aboard the space station (assuming there is such a thing) is in a constant state of free-fall. If you ever get a chance, ask one if they constantly feel their stomach rising in their chest. I've got five bucks that says the answer is "no".
A different world cannot be built by indifferent people.

Re: Freefall
« Reply #9 on: March 10, 2007, 10:37:45 AM »
An astronaut aboard the space station (assuming there is such a thing) is in a constant state of free-fall. If you ever get a chance, ask one if they constantly feel their stomach rising in their chest. I've got five bucks that says the answer is "no".

I'm referring to freefall that causes movement towards the center, not centripetal movement.  They're also in a state of weightlessness.  You're not going to prove my point invalid since you can experience it easily in an elevator, car (going over a big bump and dropping again), etc. so you FE'ers might as well start formulating one of your crazy answers.

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EnragedPenguin

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Re: Freefall
« Reply #10 on: March 10, 2007, 10:43:18 AM »
I'm referring to freefall that causes movement towards the center, not centripetal movement.  They're also in a state of weightlessness.  You're not going to prove my point invalid since you can experience it easily in an elevator, car (going over a big bump and dropping again), etc. so you FE'ers might as well start formulating one of your crazy answers.

My point was that the feeling is psychological. It has nothing to do with inertia or acceleration.
A different world cannot be built by indifferent people.

Re: Freefall
« Reply #11 on: March 10, 2007, 10:48:18 AM »
My point was that the feeling is psychological. It has nothing to do with inertia or acceleration.

I'd advise reading my second post on this thread first.  It can easily be explained with physics, and it probably wouldn't be hard to test whether or not your stomach literally rises in your chest.

I'm really interested in hearing how it's a psychological effect... Why our stomachs? Why rising?  What's causing these sensations?

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EnragedPenguin

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Re: Freefall
« Reply #12 on: March 10, 2007, 10:54:06 AM »
I'm really interested in hearing how it's a psychological effect... Why our stomachs? Why rising?  What's causing these sensations?

When you're not weightless (i.e., standing on the ground) your stomach will be held in place in your body cavity by stretched muscles. In free fall, your stomach finds itself in a position in your body cavity that it does not normally occupy. This abnormal situation is registered by the brain, triggering the physiological responses that makes your stomach feel different in free-fall. Your body is reflexively tensing the abdominal muscles in an attempt to hold the stomach in its normal place.
A different world cannot be built by indifferent people.

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EnragedPenguin

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Re: Freefall
« Reply #13 on: March 10, 2007, 10:55:13 AM »
This is from one of the articles you quoted
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the elevator's fall has made the stomach lose weight, and the elastic tissues that support it have pulled it upward. When the elevator stops descending, gravity resumes control. The stomach regains its weight and settles back into place.

By the way, when I said astronauts wouldn't feel the effect, I was mistaken. I owe you five dollars.
« Last Edit: March 10, 2007, 10:59:38 AM by EnragedPenguin »
A different world cannot be built by indifferent people.

Re: Freefall
« Reply #14 on: March 10, 2007, 12:30:41 PM »
I'm not entirely sure this shows the difference between gravity and an accelerating Earth. Straight off I'd just like to clarify that I think FE theory using the equivalence principle is a total bastardization of Einstein's science and by simply observing the universe around us we can see we are not in the situtation that FE proposes.

Anyway here is what I think about this particular idea.

First in RE model, the stomache moves "up" as it gets "left behind" due it's own inertia. Pretty simple really. eg. You're standing on a cliff and you walk off the edge. Your body accelerates at g but because your innards are not firmly attatched to your skeleton but instead elastically tethered they do not initially fall and the body moves down leaving them where they are in space for just a split second giving the impression that they moved up.

Okay so in FE model what happens if you walk off a cliff. Well before you do, the cliff (by being directly attatched to Earth) is accelerating you at g. You step off the cliff and thus continue at whatever velocity you were at (let's not worry about wind resistance for any of this discussion). Now the way I see it, the elastic material (forgive my poor biology knowledge) that holds your stomache in place is more contracted at the bottom than at the top. In effect your stomache rests near the bottom it's cavity as the cavity attatched to your body pushes up on it, just like you rest at lowest point you can on Earth as it pushes up on you. Once you are not being pushed by the Earth this translates through your body and hence you are no longer pushing up on your stomache and the squashed material underneath it springs back causing the stomache bounce upwards before settling again.

That's they way I see it.