If you imagine yourself at the center of the earth your are floating since the pull is the same around you. But let us say you could turn up the gravity as much as you want. Why aren’t you pulled apart? The net forces are zero, sure. But wouldn’t the body experience tension?

Question

If we compare it to a rope pulled by two equal forces in each end. The net forces would be zero and you would have static equilibrium, but the rope would still break if pulled hard enough.

Additionally, wouldn’t a metal ball uniformly surrounded by powerful magnets be pulled apart as well?

I am not sure why I can’t wrap my head around this, when it comes to the center of the earth.

In: 83

Answer 1

Another important aspect that sets gravity apart is that gravity is a *body force*, which means that it acts everywhere, including the inside of objects (their “bodies”). That’s different from other forces that act only on the surface (like pressure from a fluid) or on points of contact (like the ropes pulling your arms apart).

In a uniform gravity field (the Earth’s surface is a good approximation for us) the force of gravity pulls on every atom in your body with the same force (or, rather, acceleration), so there’s no tension between any internal part. A rope tied to your hand, on the other hand, is only pulling on your hand, not on the rest of your arm or body, which is why it hurts.

If you were floating in space, and a uniform gravitational field suddenly appeared, you wouldn’t feel anything, *no matter the strength of the field*, because every atom in your body would be pulled with the same acceleration. You would actually feel just as weightless as when you were floating in free space. That’s what body forces do.

Real gravitational fields from finite objects aren’t exactly uniform, of course, so other effects, like tidal force (atoms in your body a little closer to the source are pulled a little more strongly), become relevant. But these are second-order effects.