How are gravity and friction related?

Answer 1

They're not. Gravity is a conservative force and friction is a non-conservative force. This means that the amount of energy expended while in motion opposing these forces varies. When moving in a gravitational field, energy is needed only to move upwards, opposing gravity. No energy is needed to move perpendicular through the field. Think of when a football is thrown through the air. The ball leaves the quarterback's arm and arrives at the receiver traveling almost at the exact same speed (neglecting wind). In contrast, consider moving a heavy book across the top of a table. The longer the path taken to move the book, the more energy is expended.

I guess a small connection may be that without gravity, there would be no force pushing things down, which would remove friction in some cases. But friction is involved in almost every physical system, such as things when rotate.