When an object falls through vacuum, gravitational potential energy is converted to kinetic energy. Is there some way to get electrical energy out of the equation by itself (i.e. somehow convert the gravitational potential energy to electrical energy)? Is this physically possible? If so, what properties must this object have?
By by itself, I mean without using any external (possibly stationary) "reference object" (e.g. a stationary coil), so a magnet falling through a coil does not count, i.e. the electricity is generated solely by the object that is falling. Note that the object itself can be arbitrarily complex internally, just that whatever mechanism it has inside must also be falling along with the object.
Best Answer
A sufficiently large object will experience differential gravity ("tidal force") - this could be converted into a small amount of electrical energy by having two heavy spheres separated by a long rope; as they fall there will be a tension on the rope and you could let that tension do work on a generator / dynamo ("complex but internal to the object")
The concept here is that a ball closer to the earth will experience greater force and so fall a little bit faster - in the extreme case of falling to a black hole this leads to "spaghettification " but on a more normal scale it could give you a little bit of electricity. But without en external electric or magnetic field I can think of no way to convert most of the kinetic energy into electrical - the ability to do so would be a first step to an antigravity system. Let me know when you get there!