Where is the bottom of a sphere, if it is 100% isolated, with no surrounding surfaces or environment?

Question

And it's moving, without weight?

Answer 1

Technically speaking, there's no such thing as the bottom of a sphere.  That the south pole is considered the bottom of the Earth is completely arbitrary, so you can pick any point on the sphere you want to be the bottom.

If the sphere were accelerating, you could call the point opposite the accelerating force the bottom.

If the sphere had a magnetic field, you could call the south magnetic pole the bottom.

If it were spinning, you could pick either geographic pole.

or you could toss a dart at it and pick the point where the dart hits.

Answer 2

One thing that is really great about Physics is that you get to pick any point you want and happily declare, "This point is the top!".  After you make that declaration, the point on the opposite side inherits the title of bottom.

By the way, your declaration that it is moving requires a frame of reference.  You can only state that it is moving in reference to some environment, but you have already said there is none.  It is NOT moving.

Answer 3

Since there's nothing around it to give any sense of "up" or "down", all points on the sphere are equivalent, which means that there is no "bottom" of the sphere.

Answer 4

If you consider the direction of the angular velocity vector of a rotating sphere (usually used when talking about torque) as the "top" of the sphere, I guess you might consider the opposite direction as the "bottom" of the sphere.

The right hand rule says that if you imagine curling the fingers of your right hand in the direction of rotation, your thumb will point in the direction of the angular velocity vector

http://physics.ucsc.edu/~josh/6A/book/to...

Answer 5

it's similar to earth where there is no upside or downside...the north pole and south pole is just the same if there is no magnetic poles..people  stand and walk on it and feel the gravity.  we wouldn't know the difference until we moved into space and realized that it's actually a 3 dimensional world.  however our mind is capable of perceiving time as a fourth dimension and the countless dimensions in linear algebra which we made up by imagination.