The term rolling friction refers to the resistance created by an object rolling across a surface. Synonymous terms include rolling drag and rolling resistance.
Understanding Rolling Friction
The amount of friction created by a rolling object is less than the friction created by normal force. It is dramatically less than other types of friction, such as sliding friction.
The actual rolling friction can be measured and expressed as a number multiplied by the normal force.
There are various factors that can affect rolling friction such as:
- Shape of wheel
- The type of surface on which the wheel is rolling
- Any movement of the surface or below the surface
- Original speed of the wheel
- Diameter of the wheel
- Amount of pressure on the wheel
- Adhesion of the surface
- Any amount of sliding that occurs in addition to the rolling motion
- Deformation of object or of surface
- Over inflation of tires
- Thickness of tread on tires
- Shape of tread on tires
- Material that wheel or ball is made of
Any ball or wheel has rolling friction when rolled on a surface. Some examples of items that have rolling friction are:
- Truck tires
- Ball bearings
- Bike wheels
- Soccer ball, basketball, or baseball
- Car tires
- Skateboard tires
- Railroad steel wheels
- Bowling ball
Everyday Examples of Rolling Friction
- A car will eventually come to a stop if just allowed to roll as the friction between the road surface and the wheels causes friction that causes the vehicle to stop.
- Bike wheels that are thicker will lessen the potential speed of the bike because there is a greater wheel surface to create friction against the surface which will slow the bike.
- Heavy duty trucks get greater gas mileage when tread begins to wear on the tires because there is less rolling friction, allowing the truck to move more quickly with less resistance.
- A skateboard set on a slight decline will eventually stop itself because of the resistance caused by the friction between the wheels and the surface.
- A soccer ball kicked across a grassy field will slow more quickly than one kicked across a smooth, hard surface because the rolling friction is far greater on the field.
- When a train goes around a curve there is greater rolling friction.
- Roller skates have greater rolling friction than Rollerblades because there is more surface-to-wheel contact on roller skates.
- A duckpin bowling ball is likely to have less rolling friction than a full size bowling ball because of its size and weight which create less rolling friction.
- A dump truck will have greater rolling friction than a small car because the dump truck is a heavier load bearing down on the wheel and therefore causing greater rolling friction.
As you can see, many everyday objects use rolling friction. There are examples everywhere in the world.