What is the gravitational analog of an electrical ground if here is such a thing?

Question

I have an extra credit problem for my physics class. The situation involves an electron sitting between two grounded infinite conducting planes. You need to find the E-field and the potential everywhere etc. It goes on to ask: "Why can't a similar construction be done for gravity? What would it mean to have a 'grounded' object in this case? What would you have to do to set the gravitational potential to zero in some region?" I am unable to make the connection. Help is appreciated.

Answer 1

Ground means equivalent to the potential infinitely far away, which we usually call zero. To have a zero potential in the vicinity of a charge requires the existance of an opposite charge to negate its effect somewhat. Gravity is ALWAYS attractive, so the potential is always negative, so you do the same thing to get to zero.

Answer 2

A ground is a point in a circuit that is at 0 potential with respect to the rest of the circuit. But this is an arbitrary designation - the zero could be set elsewhere and the point that was ground is now at some potential relative to the new "ground".

There is no real analog in gravity - the concept of setting some point to have zero potential energy is used all the time to simplify computation of gravitational potential energy problems. In teh full blow theroy of gravity, general relativity, these zeros are local (restricted to some small vloume of space-time) and again are set for computational convienence. But there is no "global" zero point.

Answer 3

Gravity can never be zero.

It extends out to infinity, and their is no anti-gravity to ever neutralize it. That is why even though it is the weakest field, it can grow strong enough to form black holes.

The closest you can get, is two opposing objects in orbit around each other, at the libation point were they neutralize each other's pull. But even then, gravity from the other objects in the universe are not affected by this.

There are some ideas about setting up a space station at that point between the earth and the moon. I think it is not practical since the energy required to maintain the station at that position would be too great since the moon is revolving around the earth, whereas a stable orbit requires no constant energy output.

It is also said that nothing can ever escape the gravity of a black hole, but I have the theory that if two black holes are in orbit, there is a libation point between them where gravity is neutralized enough to allow matter and/or energy to escape.

Answer 4

The gravitational potential is zero if there is no other mass or when the particle is mid way between other masses of equal size