# What is Rolling Friction?

Physics

## definition

### Types of Friction

There are 2 types of coefficients of friction.
1. Static
2. Kinetic
The static coefficient of friction is more than or equal to Kinetic coefficient of friction.

## definition

### Rolling and sliding friction

When a body slides (moves with all its surface area in contact) over another body, the resistance faced is due to sliding friction. On the other hand, if a body rolls (moves with just a single point of its surface in contact) over another body, the resistance offered is a case of rolling friction.

Rolling friction is generally lesser than sliding friction. In rolling, the surfaces in contact don't rub against each other as they do in sliding friction. An example is the case of tires in vehicles. When they are moving on the road, some rolling friction acts on them. When the brakes are applied, rolling motion is reduced and sliding friction takes over to slow down the vehicle.

## example

### Rolling Friction

A solid sphere of mass is placed on a rough inclined plane as shown in the figure. The coefficient is insufficient to start pure rolling. The sphere slides a length on the incline from rest and its kinetic energy becomes . Then, the work done by friction will be given by:
Work done by friction + Work done by gravity + work done by normal force = Kinetic energy
(Work energy theorem)
work done by normal force=0
Work done by gravity is mglsin
Work done by friction =