Concepts

Class 9
Chapter 9 Class 9 - Force and Laws Of Motion

We studied Force previously as a push and pull on the body

But that is an incorrect definition.

To correct it, first lets study what force can do

## Different Effects of Force

Force can

• Move stationary object
• Stop moving object
• Change speed of the object
• Change direction of a moving body
• Change shape of a body

### Force can move stationary object

A footballer kicking a ball

### Force can stop moving object (Make Moving Object Stationary)

A fielder catches the ball

### Force can change speed of moving body

A footballer passes ball to another footballer

### Force can change direction of moving body

A batsman hitting a ball

### Force can change shape of an object

We can change shape of object by exerting force (putting force)

So, we see that the push and pull definition of force is wrong. Let's look at a new definition

## Definition of Force

We can also define force as something which can

Move a stationary object or

Make moving object stationary or

Change speed,direction, shape or size of moving body

## Questions

Q 2 Page 118 -  In the following example, try to identify the number of times the velocity of the ball changes:
“A football player kicks a football to another player of his team who kicks the football towards the goal. The goalkeeper of the opposite team collects the football and kicks it towards a player of his own team”.
Also identify the agent supplying the force in each case.

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