7. Rolling friction

You are provided with two boxes, one with wheels and another without wheels. Which one can be moved easily?

 

 

We can move the box with wheels easily when compared to the box without wheels.

Do you know the reason?

Wheels reduce friction. When we use wheels, the contact surface gets reduced; therefore, the friction between the box and the surface is less. Hence, we can apply less force to move the box.

 

When one body rolls over another body's surface, the resistance offered to its motion is called the rolling friction. Rolling reduces the friction when we compare it to the sliding friction. Therefore, one can easily roll than to slide a body over another. That is the reason it is convenient to pull the luggage fitted with rollers. Now you can understand why the wheel is one of the greatest inventions of all time.

Since the rolling friction is much smaller than the sliding friction, sliding is replaced in most machines by using ball bearings. Typical examples are the use of ball bearings in rotating shafts like ceiling fans, machines etc.

 

Let us finalize,

Static friction:

Static friction comes into play when we try to move an object from rest. 

Sliding friction:

Sliding friction comes into play when an object is sliding over another.

Rolling friction:
When one body rolls over another body, rolling friction comes into play. Rolling friction is smaller than sliding friction.

 

The order of friction is given below,