Static Friction, Sliding Friction and Rolling Friction

Friction is of three types

• Static Friction
• Sliding Friction
• Rolling Friction

Let's study each of them

Static Friction

Static friction is the frictional force which keeps the object at rest.

Example

A rock is lying on mountain slope

It is not moving down inspite of the slope

This is because of static friction between the rock and the slope

We have to move the rock by pushing it(applying a force),only then it will fall from mountain

Sliding Friction

Sliding friction is the frictional force on the object when the object is moving (or sliding) over a surface

It is also called Kinetic Friction

Example

child sliding down through a slide in a park

Skis sliding in snow

Which is Smaller- Static or Sliding Friction?

Sliding friction is always smaller than Static friction

This is because it is easier to keep a moving object moving (Sliding friction)

But it is more difficult to make a stationary object to move(Static friction)

Example

It is easier to push a moving car but more difficult to push a car which is standing

Reason

When the object is in motion, the irregularities of the moving object doesn't get much time to interlock with the irregularities of the surface.

Since the interlocking is less, the frictional force will be smaller

Hence, Sliding Friction is smaller than Static Friction

Rolling Friction

Rolling friction is the frictional force on the object when the object rolls over a surface

Example

If we move a heavy bag, it is very hard to move

But if we move a heavy bag containing wheels, it is much easier

This is due to less friction because of rolling of wheels

Since it is easier to roll than to slide

So, Rolling friction is less than sliding friction

Difference between Static, Sliding and Rolling Friction