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# Types of Friction and its Concepts

### Key Concepts

2. Sliding friction

4. Fluid

5. Fluid friction

## Introduction

Friction acts when a wheelie is placed between the object and the surface and even when it is not. There are different terms used for friction, which acts when solid-solid interaction is there, solid-liquid interaction is there, and solid-gas interaction is there. In this session, we are going to read and learn about each one of them.

## Friction:

Friction is the force that opposes or resists the relative motion between the two surfaces of objects in contact. It always acts in the direction opposite to that of the applied force or in the direction opposite to which an object moves or tries to move. It is a contact force.

Its SI unit is the same as the force that is Newton (N).

It is of different types:

1. Static friction
1. Sliding friction
1. Rolling friction
1. Fluid friction

Let us learn about each one of them.

### Static friction:

Static friction force counterbalances the force applied to a body. It is also known as self-adjusting force.

It comes into play until an object starts to move. An object needs to overcome the static friction force in order to start its movement.

For example – Frictional force acts when a boy pushes a sofa, and the sofa does not move.

### Sliding friction:

Sliding friction comes into play when one surface is sliding over another surface. Sliding friction is the force that opposes the movement or slide of an object.

For example: Frictional force acts when a boy pushes a sofa and sofa is moving.

### Rolling friction:

When a surface is rolling on another surface, the force of friction that acts upon it is called rolling friction

For example – A boy pushing a bag with wheelies.

### Fluid friction:

Air or liquid are known as fluid. Friction exerted by fluids(gases and liquids) is termed fluid friction.

For air, it is called air resistance or air friction. Example: a person sky diving.

For water, it is known as viscous friction or drag. Example: fish or submarines moving in the water.

It depends on many factors such as:

1. Nature of the substance (denser/rarer)
1. Shape and size of the object
1. Speed of the object

Question 1: Suppose your writing desk is tilted a little. A book kept on it starts sliding down. Show the direction of frictional force acting on it. Which type of frictional force is acting on it?

Question 2: Explain how the fluid friction depends on each one of them using real-life examples?

1. Nature of the fluid: Denser fluid has high fluid friction.
1. Shape and the size: Broad shape and bigger size, respectively, have high fluid friction.
1. Speed of the object: As the speed increases, the fluid friction also increases

### Summary

• Friction is of the following types:

a. Static friction: the friction which counterbalances the force applied. The object does not move.

b. Sliding friction: the friction offered when the object slides over another object

c. Rolling friction: the friction offered when the object rolls over another object

d. Fluid friction: the friction offered by air or water.

• Fluid friction depends on

a. Nature of the fluid (denser/rarer)

b. Shape and size of the object

c. Speed of the object

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