The resistance offered to the movement of one body past another body with which it is in contact. The amount of friction depends on the nature of the contact surfaces and on the magnitude of the force pressing the two bodies together, but not on the surface area of the contact surface.

Dry film lubricants offer very unique performance properties when friction is a concern. In most cases, solid film lubricants provide a lower coefficient of friction than traditional wet lubricants. Much of this improved performance comes from the resin's lubricating properties. Depending on the resin system, the lubricant can substantially decrease both the static and dynamic friction. Due to their performance properties, many of these dry film lubricants are used for performance problems associated with rolling and sliding friction.

There are two kinds of friction: static friction and kinetic friction:

Static friction is the force between two stationary objects. Static friction is always greater than kinetic friction. In fact, at the momentary point when objects start to move in relation to one another, the friction, called starting friction, is at its highest.

You may recall when you try to move a heavy object, the most force is required to start it moving. Once an object is in motion, it tends to stay in motion.

There are several types of kinetic friction, including sliding friction and rolling friction. Sliding friction, flat objects moving against each other, is greater than rolling friction, a rolling object moving against a surface. (This principle is applied in ball bearings.)