Concepts

Class 8
Chapter 12 Class 8 - Friction

## What are fluids?

We know that there are 3 forms of Matter

• Solids (Example - Ice)
• Liquids (Example - Water)
• Gases (Example-Water Vapour)

Fluid is the common name given to liquid and gases

## Is force of friction only exerted by solids?

No

It is exerted by all forms of matter-solids or fluids(liquid and gases)

## What is fluid friction

Frictional force exerted by liquids and gases is called fluid friction

It is also called Drag or Drag Force

#### Example 1

When an aeroplane flies in air,it faces resistance from air which reduces its speed

This air resistance is frictional force of air or fluid friction

#### Example 2

When a speedboat moves in sea,it faces resistance from water in the sea which reduces its speed

This is frictional force of water or fluid friction

## Factors which Effect Fluid Friction

### Speed of Object

More the speed of object,more will be fluid friction.Less the speed ,less the fluid friction

Example A speed boat will face more friction compared to a paddle boat

### Shape of Object

If object is streamline(pointed from front),they face less fluid friction

But if object is not streamlined,it faces more friction

Example - A truck will face more friction compared to a car

### Size of Object

larger the size of object,more the friction

Smaller the size,less the friction

Example - A ship will face more friction compared to a boat

### Nature of fluid

If fluid is more viscous or thick,there will be more friction

If fluid is less viscous or thin,there will be less fiction

Example - Water is thicker than air,so there is more friction in water compared to air.This is why aeroplanes move faster than ships

## Why it is important to reduce fluid friction?

It is important to reduce fluid friction because

### Reduces Speed

Fluid friction reduces speed of vehicle.(If there was no friction,vehicle would move faster)

### Increase Costs

it reduces efficiency and increase cost of running vehicle(More fuel is required to overcome fluid resistance)

## How to Reduce Fluid Friction?

Fluid friction is reduced by streamlining shape of vehicle

This is done by making it pointed from front like a bird

Also wings are provided in case of aeroplane

This help in reducing air resistance and increasing speed and efficiency of object

#### Example 1

Front of Aeroplanes are pointed .They also have wings,This reduces friction in air and make aeroplane travel faster

#### Example 2

Boats and Ships are also pointed in front.This reduce friction in water

#### Example 3

Similarly, car is also streamlined to reduce air resistance (or drag)