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jroberson
2012-Feb-07, 10:26 PM
I've heard many people say that "gravity on Jupiter (or other large massed celestial body) will crush you...but, if gravity is a force between you and that planet...how can it be "crushing"? This is like saying gravity is a downward push towards Earth...rather than an attractive force...which would be incorrect...

It would also be like saying that a falling object that breaks was crushed by gravity...

Thoughts?

Jens
2012-Feb-08, 12:11 AM
It seems a bit semantic to me, but it's true that gravity won't crush you no matter how strong it is. The problem is the fact that the surface stops you from falling any further or that the matter pulled by the gravity makes a high pressure soup that will crush you. Maybe it's a bit the same as the fact that falling off a building never hurts anyone, the problem is the sudden stop at the bottom. So I guess you're right but I'm not sure if it's very important.

cjameshuff
2012-Feb-08, 05:06 AM
I've heard many people say that "gravity on Jupiter (or other large massed celestial body) will crush you...but, if gravity is a force between you and that planet...how can it be "crushing"? This is like saying gravity is a downward push towards Earth...rather than an attractive force...which would be incorrect...

It would also be like saying that a falling object that breaks was crushed by gravity...

More like a building that collapses was crushed by gravity, which really isn't all that inaccurate. The attractive force is on your entire body, but the parts resting on the surface must support the parts resting on them and so on, and given a solid surface to stand on and strong enough gravity, you will be crushed by your own weight.

Jupiter's gravity isn't particularly crushing, though. You'll weigh about 2.5 times as much at the altitudes generally considered the "surface". You probably won't be tap dancing, but you probably won't collapse under your own weight either. The only body in the solar system approaching "crushing" gravity is the sun, at about 28 g.

Jeff Root
2012-Feb-08, 05:20 AM
I don't recall ever reading or hearing anyone say that
Jupiter's gravity would "crush" a person. I know I have
read and heard numerous times that Jupiter's enormous
atmospheric pressure would crush a person. Of course,
that pressure is caused by Jupiter's gravity.

-- Jeff, in Minneapolis

Strange
2012-Feb-08, 11:56 AM
This is like saying gravity is a downward push towards Earth...rather than an attractive force...which would be incorrect...

Well, your head would push down on your neck bone. The combined weight of those would push down on your backbone, which would push down on leg bones ... So you would crush yourself, I guess.


The head bone connected to the neck bone,
The neck bone connected to the back bone,
The back bone connected to the thigh bone,
The thigh bone connected to the knee bone,
The knee bone connected to the leg bone,
The leg bone connected to the foot bone,
The foot bone connected to the heel bone,
The heel bone connected to the toe bone...

neilzero
2012-Feb-09, 02:12 AM
According to Isaac Azimov, many years ago, the cloud top gravity of Jupiter is 2.75g, so an athletic person in a balloon habitat would be uncomfortable, but not crushed. Likely the gravity increaces only slightly below the cloud tops, but the atmosphereic pressure increases rapidly.
Saturn has a cloud top gravity of one, so that would be optimum for humans.
I've heard that the cloud top gravity of a cooled brown dwarf is about 100g, so that would be crushing. Neil

tony873004
2012-Feb-09, 02:16 AM
Jupiter's cloudtop gravity is about 2.5 times that of Earth's surface gravity. I doubt that would crush you.

Xibalba
2012-Feb-13, 01:52 AM
If you are not standing up, but rather laying down, your neck won't be broken by the weight of your head. That or you can still train your neck muscles till you look like a bull.

This way, in a controlled environment, where the atmosphere can't crush your body, you could experience the weight of an obese person while keeping your body shape. If you are an obese person, imagine supporting another obese person on your back.

The controlled environment would need to have an atmosphere which is less dense than Earth's, even though I don't think Earth's atmosphere multiplied by 2,5g will crush you anyway. Maybe Venus' will, though.

But then, a fall of only a few inches might lead you to a broken leg.

transreality
2012-Feb-13, 03:29 AM
As you fall towards a Black hole say, don't you get stetched apart by tidal forces, rather than crushed?

cjameshuff
2012-Feb-13, 04:03 AM
The controlled environment would need to have an atmosphere which is less dense than Earth's, even though I don't think Earth's atmosphere multiplied by 2,5g will crush you anyway. Maybe Venus' will, though.

You'll run into problems with dissolved gases long, long before the pressure gets high enough to directly harm you. Gas-filled parts of the body can be brought to equilibrium with the outside, the rest is essentially incompressible. Even if you managed to work around the dissolved gas issue enough to get killed by the pressure itself, you wouldn't be crushed, you'd die because of the changes in chemical reactions and structures under high pressure. We're talking about hydrostatic pressure here, not a trash compactor.

swampyankee
2012-Feb-14, 12:43 AM
Balanced hydrostatic pressures won't crush you, at least until some components of your body start having pressure-related changes of phase. I believe the record dive, to about 610 meters, resulted in a pressure of about 6 megaPascals, so there's no crushing at about 60 times sea level pressure. I have no idea where pressure effects will start disrupting human biochemistry.

Being crushed by gravitational forces is a different issue. Materials can fail in compression by buckling, which, in the simplest case, is modeled by Euler's Formula for column buckling, and by compressive failure. You could check out wikipedia's (I know, I know) bit on self-buckling ( http://en.wikipedia.org/wiki/Buckling#Self-buckling).

Xibalba
2012-Feb-14, 12:59 AM
Wow, even at 61 atm, our body is able to compensate and survive. Although I bet we wouldn't live long at these pressures. I think you'd get nitrogen in your blood, or something like that. I don't do diving so I don't know much.

swampyankee
2012-Feb-14, 03:14 AM
Wow, even at 61 atm, our body is able to compensate and survive. Although I bet we wouldn't live long at these pressures. I think you'd get nitrogen in your blood, or something like that. I don't do diving so I don't know much.

Actually, my earlier post was wrong: it's not about 610m; it's about 700 m. See http://www.divingalmanac.com/article.php?article_id=756

As for nitrogen in the blood: it would be a problem, if they used nitrogen in the breathing mixture: they don't. For depths much over 100m, the divers breathe a mix of helium, oxygen, and possibly hydrogen.

JCoyote
2012-Feb-14, 03:39 AM
Gravity can collapse protons and electrons into neutrons and beyond that into singularities. If that isn't crushing in a spectacular way, I don't know what is.

WayneFrancis
2012-Feb-14, 05:12 AM
I've heard many people say that "gravity on Jupiter (or other large massed celestial body) will crush you...but, if gravity is a force between you and that planet...how can it be "crushing"? This is like saying gravity is a downward push towards Earth...rather than an attractive force...which would be incorrect...

It would also be like saying that a falling object that breaks was crushed by gravity...

Thoughts?

Ok, it isn't the gravity that directly crushes you. What can crush you is the cells in your body that are further from the centre then those that are closer. Your own body will crush you even if Jupiter had a surface and no atmosphere, depending on radius of the surface.