# Chapter 12 Class 8 Friction Notes Pdf

## Short & Concise Friction Class 8 Notes

Firstly, let us see what we are going to study in this chapter. The overview of the chapter is very necessary for every student. This gives you an idea about the content we are going to study and can relate to our previous syllabus or chapters.

Let us first see what we are going to study-

Here is the list of topics we are going to discuss in this chapter 12 Friction.

• What is Frictional Force
• Types of Frictional Force
• Static Friction
• Kinetic Friction- Sliding and Rolling
• Methods of Increasing Friction
• Methods of Reducing Friction
• Why Friction is called a necessary evil?

### What is Friction?

What is the Force of Friction or Frictional Force?

It is the force that comes into action when the surfaces of two bodies come in contact with each other and it opposes the motion of the objects.

• It is not a fundamental force.

### Causes of Friction

What causes friction? Friction is caused due to the following-

• Irregularities– Due to the roughness or the irregularities present on the surfaces in contact. The surfaces get interlocked.
• Forces of attraction– Due to the presence of adhesive forces (force of attraction between the molecules of the two surfaces in contact).

### Types of Frictional Force

There are mainly two types of Frictional Forces-

1. Static Friction
2. Kinetic Friction (Sliding Friction & Rolling Friction)

#### Static Friction

The frictional force that acts on a body when it is stationary (at rest). A body starts moving when the force applied is greater than this Static Friction.

#### Kinetic Friction

Kinetic Friction comes to play when an object starts moving (Sliding or Rolling), it is called Kinetic Friction.

Static Friction > Kinetic Friction

Also, Static > Sliding > Rolling

#### Sliding Friction

When a body slides over another body, it is called sliding friction.

Example: Dragging a box on the floor.

#### Rolling Friction

When a body rolls over another body, the friction acting between the surfaces is called rolling friction.

Example: Wheels rolling on the road is the best example of rolling friction.

What are the Advantages and Disadvantages of Friction or Force of Friction?

Friction is something that opposes motion and is often considered evil. But Friction also plays an important part in our daily life. There are many advantages of Frictional Force. Let us look into some Advantages of Frictional Force.

• Help us to walk on the ground
• Friction helps us to write on the notebook or board.
• Friction helps us to hold things.
• We fix the nail on the wall easily because of friction, which helps in holding the nail.
• A moving vehicle comes to rest on applying brakes due to friction.
• Due to air friction meteoroids burn up or get reduced in size before entering the earth’s atmosphere.

### Methods of Increasing Friction

Since the Force of Friction plays a very important role in our day-to-day life; it is sometimes necessary to increase friction.

• By making the surface rough which is in contact
• To avoid slipping, shoes are grooved.
• By increasing the mass of the object, friction is increased.

Friction has many disadvantages. The main disadvantages are that it is due to friction the efficiency of any machine is decreased. It causes wear and tear of moving parts of the machine and thus decrease its life. Now, let us discuss some disadvantages of frictional force.

• It causes wear and tear.
• Due to friction, extra energy is consumed.
• Friction also produces noise.
• Friction decreases the efficiency of a machine
• Frictional Force produces a lot of heat
• Friction decreases the life of machines

### Methods of Reducing Friction

Since Friction is called evil; there are many methods of reducing friction by making the surfaces in contact smoother.

• Lubrication: Surfaces can be made smoother by using oil, grease, etc.
• Sprinkling powder like on the surface of a carom board
• Use of Ball Bearings
• Making objects streamlined
• Helping objects to roll instead of sliding

### Why Friction is called a necessary evil?

Friction is often referred to as a “necessary evil” because it has both benefits and disadvantages.

It plays an important role for everyday activities like walking, driving, and writing, etc. as it provides the grip needed to perform these actions safely and effectively. However, friction also causes wear and tear on materials, wastes energy by generating unwanted heat, and makes moving objects more difficult.

Despite its drawbacks, friction is crucial for many fundamental tasks, which is why it is called necessary evil.

### What is Drag?

The opposing force (frictional) exerted by the fluids (Air or Water) on a solid object is called Drag.

• It depends on speed, the shape of the body, and the nature of the fluid.