1.1 Friction
The phenomenon impeding the tangential relative movement between contact surfaces of two objects.
1.2 Friction by sliding
The friction generated in the case that the contact points of two contact objects moves at different speeds.
1.3 Friction force
The resistance to friction when two objects move toward opposite direction.
1.4 Friction coefficient
The ratio of the friction force impeding the relative movement of two objects to the normal force acted on the object surface.
1.5 Wear
Continual loss or residual deformation of substances on surfaces of two contact objects in relative movement.