Friction

Friction may instead increase the thermal energy stores of those parts and their surroundings. The energy has not disappeared: it has been dissipated and is now less useful.

The brakes oppose the wheels' motion, while friction between the tyres and the road provides the grip needed for the vehicle to slow without simply sliding.

Friction acts between surfaces in contact and opposes their relative movement, or their tendency to move, across one another. A sliding box experiences friction from the floor in the direction opposing its slide. Friction can also be helpful: when walking, friction between a shoe and the ground prevents the shoe from slipping and allows the person to push against the ground.

Contact interactions include normal contact forces and friction.