Force Changes Speed And Direction


 
 
Concept Explanation
 

Force Changes Speed And Direction

Force can change the Speed of a Moving Object

To change the speed of an object certain force has to applied. If the force is applied in the direction of motion of the object, its speed increases. On the other hand, if the force is applied in the direction opposite to the direction of motion of an object, then its speed decreases. For example

1.  A bicycle is moving at a certain speed.and if someone pushes the moving bicycle from behind, then the speed of bicycle increases and it will start moving faster. On the other hand, if someone pulls he moving bicycle from behind, then the speed of bicycle decreases and it will start moving slowly. Thus, a push or pull that is force can change the speed of a moving bicycle.

 

2. When a ball is dropped from a height, its speed goes on increasing. The speed of a falling object increases because the Earth pulls a falling object towards its centre because of gravity and increases its speed  On the other hand, when a ball is thrown upwards, then its speed goes on decreasing. This is because the earth applies a pulling force of gravity on the ball in the downward direction opposite to the  motion of the ball.

3. When a hockey player hits a moving  ball, the speed of ball increases.

4. When we pedal the bicycle faster, then the speed of bicycle  increases. And when we apply brakes to the moving bicycle, then the speed of bicycle decreases.

On analysing all these examples we conclude that a force can change the speed of a moving object.

A Force can Change the Direction of a Moving Object:

To change the direction of an object certain force has to applied. For example

1. In a cricket match, when a moving cricket ball is hit by a bat, then the direction of cricket ball changes and it goes in another direction. In this case, the force exerted by bat changes the direction of a moving cricket ball.

2. In the game of carrom, when we take a rebound, then the direction of striker changes. This is because the edge of the carrom board exerts a force on the striker.

3. If we blow air from our mouth on the  smoke rising up from a burning agarbatti, then the direction of motion of smoke changes. In this case, the force exerted by the blowing air changes the direction of moving smoke.

On analysing these examples we conclude that a force can change the direction of motion of a moving object.  The state of motion of an object is defined by its speed and the direction. A change in either the speed of an object, or the direction of its motion, or both, is called a change in its state of motion. A force can change the state of motion of an object.

Sample Questions
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Question : 1

Which of the following are correct ?

(a) If the force is applied in the direction of motion of the object, its speed decrease .

(b) The state of motion of an object is defined by its speed and the direction. 

(c)  A force can change the state of motion of an object.

Right Option : B
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Explanation
Question : 2

A change in either the speed of an object, or the direction of its motion, or both, is called a change in its__________________

Right Option : B
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Question : 3

In the game of carrom, when we take a rebound, then the direction of striker changes. This is because of the ________________

Right Option : C
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Explanation
 
 
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