Question

friction forces operate differently depending on whether there is between objects in contact or not. when objects in contact are moving relative to each other, friction is involved. when there is a force tending to move one object against another, but the objects are not in motion, friction forces exactly counterbalance that force.

Explanation:

Friction is classified based on relative motion. Kinetic friction occurs when objects in contact are moving relative to each other. Static friction acts when there's a force tending to move objects but they aren't in motion.

Answer:

relative motion, kinetic, static