## Force of friction

• The force which resists the relative motion of a surface is called as Friction.
• The force of friction is offered by all types of surface such as solid, liquid and the air.
• The force of friction is always applied in the opposite direction of the movement.
• When the two substance move towards each other, then friction is applied.

## Factors affecting friction

• When two surfaces are in contact then their irregularities cause friction.
• Increase in weight causes the increase in the force of friction.
• More force of friction is offered by Rougher surfaces.

## Types of Friction

1. Sliding friction
• When two surfaces overlaps then this force comes into action.
• Example is sliding of a box or book over the ground.

1. Rolling friction
• When one surface rolls on the other surface then this friction comes to an action.
• Sliding friction is bigger than the rolling friction.

## Why is friction necessary?

• Some examples which show friction is necessary are-
1. Due to the friction offered by ground, we can walk easily. Hence walking requires friction
2. Since wet marble floor or muddy tract offers very less amount of friction which makes difficult for us to walk easily on them.
3. Grooves on the soles of the shoes give good amount of friction to the ground which makes us walk easily due to the good grip.
4. Heat is also produced by friction.
5. Due to the friction provided by the paper to the tip of them pen, writing with the pen becomes possible.

### Fluid Friction

• Liquids and gases are generally termed as fluid. Fluids also provide friction just like the solids.
• With the speed of fluid and the speed of the moving object, the friction of fluid increases.
• When the fluids offer frictional force then that force is called as drag.

## Recap

• The force which resists the relative motion of a surface is called as Friction.
• The force of friction is offered by all types of surface such as solid, liquid and the air.
• The force of friction is always applied in the opposite direction of the movement.
• When two surfaces are in contact then their irregularities cause friction.
• Liquids and gases are generally termed as fluid. Fluids also provide friction just like the solids.