 # Friction Class 8 Notes - Chapter 12

The class 8 science chapter 12 Friction, discusses friction and various factor affecting it. The force which opposes the relative motion between two surfaces in contact is known as friction. It acts on both the surfaces. Listed below are factors that affect friction.

## Factors Affecting Friction

Friction is affected by two factors which are

1. Nature of the Surface – Irregularities on two surfaces in contact results in friction. Irregularities on both the surfaces lock on to each other. When we try to move a surface, we need to apply force in order to overcome interlocking. Rough surfaces have more irregularities. So the force of friction is greater in rough surfaces than smooth surfaces.
2. The force with which two surfaces are pressed together – Friction increases when two objects are pressed harder.

### Types of Friction

The types of friction discussed in the chapter are

• Static Friction
• Sliding Friction
• Rolling Friction
• Fluid Friction
 Type of Friction Definition Examples Static Friction The force required to overcome the friction the instant an object at rest starts moving is a measure of static friction A heavy crate resting on the floor of a warehouse Sliding Friction The force that keeps the object moving at the same speed is a measure of sliding friction. A person sliding down a slide and a sledge sliding across the ice are a few examples of sliding friction. Rolling Friction The resistance offered to the motion create when one body rolls over the surface of another body is known as rolling friction. The friction between the road surface and wheel Fluid Friction Friction between layers of viscous fluid moving relative to each other. Occurs in liquids and gases The resistance of the air against the parachute

Friction sometimes is undesirable when it causes wear and tear of the machine due to constant rubbing against each other. Friction can be reduced using lubricants and by using ball bearings.

## Friction Class 8 Extra Questions

1. If a bucket of soapy water is spilt on a marble floor accidentally. Is it easier or difficult to walk?
2. A book kept on a table starts sliding down the table. Show the direction of the frictional force acting on it.
3. Give examples to show that friction is both a friend and a foe.

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