Atmosphere

[dmm]

quote:

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Originally posted by apache:
...anything regarding the gravitational forces at the center of a massive object is completely theoretical, and there is absolutely no experimental proof to support any of it. Therefore, taking it as a fact is something best done with a grain of salt, rather, an entire salt shaker.

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Well, I can't argue logically with that. It might very well be that everything we know about gravity goes out the window once you're near the center of a massive object. However, if I take your point of view, then the universe is unknowable. Even if I mangaged somehow to do the experiment on Jupiter, how would I know that I'd get the same result on Saturn? (On the other hand, I'd agree with you if we're talking about black holes, because the gravity is so intense that our understanding of it may not hold under such extreme conditions.)

Like all scientists, I take it as a matter of faith that the universe is comprehensible (if we're smart enough) and reasonable (if we're open-minded enough). One time Einstein was told that some experimentalists had found some tiny flaw in his general theory of relativity, which they said could be fixed by adding a high-order "fudge factor" to his theory. Einstein calmly replied, "Subtle is God, but deceitful He is not." The flaw was later shown to be an experimental artifact.

[dmm]

quote:

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Originally posted by Alpha Kodiak:

I am relativistically certain that if you place a black hole up your nose, you will no longer have any concerns about sinus congestion.

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I picked a mini black hole out of my nose the other day, and wiped it on my sock. Then it went into the laundry and I lost track of it.

[apache]

"Hmmm. I'd say that if the net gravitational force on an object is zero, that by definition, all the gravitational forces have canceled out. Gravity is not like pressure in the example you give. For a small object (relative to the size of the planet), say a person, if the net gravity is zero for that person, every point (ie: every cell, every molecule) on/in the person will have a net gravity of zero. The tidal differences between, say, points on the person's left and right arms would be too small to matter."

Here is something I can finally dispute with certainty. Using Newton's second law (assuming it applies in the center of a planet/other things), we know that the sum of all the forces acting on the object equal its the change in momentum of the object. Ok, so adding up everything via integration methods, we find that the net force on the object is equal to 0. From this we figure that the change of momentum is 0. So if the object is at rest, it will stay at rest, and if it is moving, it will continue to move (Newton's first law). Thus, we say the forces acting on the object are in equilibrium.
However, equilibrium does not mean the forces 'cancel out'. Now that we found out the forces acting on the entire object, we can then look at internal forces. So, lets cut the object in half (not actually cut it, just an imaginary cut to examine the forces on the inside). Ok, now we know that the entire body was in equilibrium, so this section of the object must also be in equilibrium, otherwise the two halves of the body would move away from eachother. However, by cutting it in half, we have eliminated the gravitational forces acting on the other half of the object (they are still there, but since we are analyzing the other half, we only get half of the gravitational forces. So what we see is that for this object to be staying in one piece is that there must be internal forces to counteract the gravitational forces (Newton's third law). This means there must be internal stresses.
From this point, knowing the internal stresses, you can compare them to the known strength of the material the object is composed of, and if the stress is too high, the object is ripped apart, if not, then it stays together.
This is much like a tug of war. Just because the rope may not be moving if each side pulls with the exact same force, that does not mean that the rope does not experience force. If those forces pulling the rope are too great for the strength of the rope, it will rip apart.

[jimbob55]

Well, my sinuses are clear, but now I have an omnivorous hole for a brain (no change there then)

Just to get things back on topic, I've posted my extensive ramblings here: http://pub41.ezboard.com/fscienceobs...opicID=2.topic

for anyone who wants to talk about physics

[Ares]

Originally posted by dmm:

quote:

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Originally posted by Alpha Kodiak:

I am relativistically certain that if you place a black hole up your nose, you will no longer have any concerns about sinus congestion.

I picked a mini black hole out of my nose the other day, and wiped it on my sock. Then it went into the laundry and I lost track of it.

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That's why I'm losing all my socks! I wipe all my picked singularities off on my sock. Furthermore, I can conclude that it's always my LEFT sock, as that's the one I always use for this purpose.

Anyone know where I can buy a package of only left socks?

[Jack Simth]

Originally posted by apache:

Here is something I can finally dispute with certainty. Using Newton's second law (assuming it applies in the center of a planet/other things), we know that the sum of all the forces acting on the object equal its the change in momentum of the object. Ok, so adding up everything via integration methods, we find that the net force on the object is equal to 0. From this we figure that the change of momentum is 0. So if the object is at rest, it will stay at rest, and if it is moving, it will continue to move (Newton's first law). Thus, we say the forces acting on the object are in equilibrium.
However, equilibrium does not mean the forces 'cancel out'. Now that we found out the forces acting on the entire object, we can then look at internal forces. So, lets cut the object in half (not actually cut it, just an imaginary cut to examine the forces on the inside). Ok, now we know that the entire body was in equilibrium, so this section of the object must also be in equilibrium, otherwise the two halves of the body would move away from eachother. However, by cutting it in half, we have eliminated the gravitational forces acting on the other half of the object (they are still there, but since we are analyzing the other half, we only get half of the gravitational forces. So what we see is that for this object to be staying in one piece is that there must be internal forces to counteract the gravitational forces (Newton's third law). This means there must be internal stresses.
From this point, knowing the internal stresses, you can compare them to the known strength of the material the object is composed of, and if the stress is too high, the object is ripped apart, if not, then it stays together.
This is much like a tug of war. Just because the rope may not be moving if each side pulls with the exact same force, that does not mean that the rope does not experience force. If those forces pulling the rope are too great for the strength of the rope, it will rip apart.

Gravitational forces act equally on all particles of mass at a given point. If you are splitting the object in half to look at it (not splitting the gas giant) then the gravitational forces from the GG still cancel out, leaving only the ones from the other half of the object that you split for consideration, which is negligable.

[PvK]

There are some gravitational shear forces. The question then becomes how strong they are, and what distances are involved, to determine how much stress they will cause. In most all cases humans are familiar with, such shear forces are too small to cause an effect, but there are some differential gravity effects we are familiar with, such as from the moon, its obvious effects (tides) and some more subtle ones.

PvK