# Rolling friction

### What is rolling friction?

For a moving solid body, there are two principal types of friction that act upon it:

• The force resisting the motion of a rolling body on a surface is known as Rolling friction or Rolling resistance. This type of friction is experienced by a wheel or a ball rolling on the ground.
• There is another type of friction known as Sliding friction, which resists the movement of a body which is pushed in such a way that only one surface of the body is in contact with the surface it is moving on. It will be experienced when, for example, a box is pushed across a table.

Rolling friction is considerably weaker than Sliding friction.

### Cause of rolling friction

When an object is rolled on a surface, certain things happen:

1. The object is deformed at the point of contact with the surface.
2. The surface is deformed at the point of contact with the object.
3. Motion is created below the surface as a result of the above mentioned points.

The primary cause of this friction is that the energy of deformation is greater than the energy of recovery. Also, there is an adhesive force between the two surfaces which needs to be overcome constantly. The amount of friction is based on a variety of factors, such as,

• The quality of the sliding body
• The quality of the surface,
• Diameter of the rolling object
• Surface area of the body

### Coefficient of rolling friction

Determining the coefficient of this friction is considerably more complex than that of sliding friction. “Coefficient of Rolling Friction is the ratio of the force of rolling friction to the total weight of the object.”

In empirical terms, the coefficient of rolling resistance can be expressed as:

$F_{r} = u_{r}W$,

where,

$F_{r}$ is the resistive force of rolling resistance,

$u_{r}$ is the coefficient of rolling resistance, and

$W$ is the weight of the rolling body

### Examples of rolling friction in everyday life

• A basketball rolled on the court will eventually come to a halt because of rolling friction.
• A bike with a broad tire will burn more fuel because of the increased rolling friction.
• A ball rolled on a field will go lesser distance than a ball rolled on a concrete floor because it will experience greater rolling friction on the former surface.