# What are the aims of measurement of coefficients of static friction and dynamic friction?

Friction or friction force resists the motion of two surfaces past each other. There are two types of frictional forces (especially when discussing the motion of objects): static friction and dynamic friction. The static friction opposes the motion of an object at rest. Once this friction is overcome, only then can the object move. Dynamic friction opposes the motion of an object that is moving. For example, a stationary car will not start moving till it overcomes the static friction between tires and road surface. And once it is in motion, the movement of car is resisted by dynamic friction.

A measure of frictional forces, through coefficients of static and dynamic friction, is necessary to determine the forces necessary to overcome the friction and ensure motion. A road surface with higher friction causes more fuel consumption, while a very smooth road surface will have lesser braking (and hence more stopping distance). Friction is also needed for walking and running and hence our shoe surfaces need to have appropriate material for ensuring that we can walk and run, without too much effort.

These are just a few examples, where we need to determine the coefficient of static friction and dynamic friction.

Hope this helps.