Atmosphere

LintMan · #1 February 2nd, 2001, 09:10 AM

quote:
Originally posted by apache:

Now, as for DMM, if you have read some of my other Posts lately, you would know that I am not going to take a theory lying down.
First of all, there is the massively disputing theory of general relativity, which essentially throws Newtonian theories out the window. I'm not gonna argue anything about it, though, since I have a limited understanding, and its all theory anyways.
Second, 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.

General Relativity doesn't dispute Newtonian physics, it encompasses them. Newtonian physics works, as we see proven every day with our satellites, rockets, and planetary astronimcal observations. The term "theory" here does not mean "completely unproven" - newtonian and GR physics have been borne out in countless scientific experiments. To say "it's all theory anyway" implies it is all completely untested and anybody's guess, which is totally untrue.

You can say we can't be sure about the gravity at the center of a planet just because we haven't measured it directly, but the world uses the math of physics to predict behavior/properties of things reliably, all the time.

quote:

Third, getting a net zero gravitational force is vectorial and mathematically correct, but the fact is that the gravitational forces could not cancel each other, putting no force on the body, they just act to keep the object at the center of the body in equilibrium, or in otherwords, they will not induce a velocity or accleration on the body as a whole in any direction.
However, if the object at the center could not withstand the forces pulling on it, it would indeed be ripped appart. Think of it like a reverse pressure. Rather than keeping an object from expanding, like air pressure acting on a balloon, it would keep an object from imploding.

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.

Cybes · #2 February 2nd, 2001, 11:03 AM

quote:
Originally posted by LintMan:
The term "theory" here does not mean "completely unproven"

yah - the term for that is "hypothesis". a theory is a hypothesis which has been shown to explain currently known facts, and predict new ones.

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"Just think of it as Evolution in action" - 'Oath of Fealty', by Larry Niven & Jerry Pournelle.

[This message has been edited by Cybes (edited 02 February 2001).]

jimbob55 · #3 February 2nd, 2001, 03:51 PM

*wanders about staring off to the horizon* Nope, can't see the topic anywhere....

If I took 2 small (say the size of a beachball) black holes and through cunning and artifice managed to get them to orbit their mutual center of gravity.....Then i stuck my head into that center of gravity, would it clear my sinuses?
Or would it just turn my head into a thin string of skull and brain matter linking the two?

I ask, because this cold cure stuff doesn't work and I happen to have 2 small black holes lying round the place.

I am just joking. Please understand that any form of medical treatment involving singularities should only be used on the advice of a doctor (possibly of physics)

Alpha Kodiak · #4 February 2nd, 2001, 06:06 PM

quote:
Originally posted by jimbob55:
*wanders about staring off to the horizon* Nope, can't see the topic anywhere....

If I took 2 small (say the size of a beachball) black holes and through cunning and artifice managed to get them to orbit their mutual center of gravity.....Then i stuck my head into that center of gravity, would it clear my sinuses?
Or would it just turn my head into a thin string of skull and brain matter linking the two?

I ask, because this cold cure stuff doesn't work and I happen to have 2 small black holes lying round the place.

I am just joking. Please understand that any form of medical treatment involving singularities should only be used on the advice of a doctor (possibly of physics)

I think the correct treatment, assuming a small enough singularity, would be to insert the singularity into the sinus cavity to promote drainage. Of course, I am not a doctor, I only play one on TV. Ok, ok, I only dream of playing a doctor on TV. Actually, I'm just a software engineer, but I am relativistically certain that if you place a black hole up your nose, you will no longer have any concerns about sinus congestion.

dmm · #5 February 2nd, 2001, 06:31 PM

quote:
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.

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 · #6 February 2nd, 2001, 06:35 PM

quote:
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.

apache · #7 February 2nd, 2001, 07:55 PM

"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.