Question

why friction is always acts in the opposite direction of motion

Answer 1

friction always act opposite to the motion Because. it try to stop motion

Answer 2

Why is friction always opposite to the motion?

Friction always acts in the opposite direction to movement, i.e. it opposes the motion of an object. Air resistance is a frictional force which opposes motion through air. Frictionalforces can be useful, e.g. to allow car tyres to grip the road or to slow down a falling parachutist.