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# Force and Laws of Motion

Tutormate > CBSE Syllabus-Class 9th Physics > Force and Laws of Motion

## 02 Relation Between Force and Motion

• Force and motion are related and force is the cause of motion, as force affects the state of motion of an object.
• An object moves when some force acts on it or has acted on it which produced this motion.
• Motion can either be described as
• Change in speed, or
• Change in direction.
• From the studies of Sir Isaac Newton, three conclusions can be made on force and motion:
• Force can cause a body to accelerate
• Force can cause a body to change directions
• Force can cause a body to decelerate

#### FORCE CAN CAUSE A BODY TO ACCELERATE

• A body at rest starts moving when a force is applied to it, provided that there is no greater force opposing it.
• For example, when a bowler throws a ball, it starts to move forward from its initial position of rest in his hands.
• When something begins to move from a state of rest, it accelerates. Acceleration can be described as the positive change in velocity over a period of time.
• If force is applied in the same direction of movement of a moving object, it accelerates. For example, rotating the pedal of a bicycle will make it go faster.

#### FORCE CAN CAUSE A BODY TO CHANGE DIRECTIONS

• An object changes motion when force is applied on it in an angle different to its direction of motion. Almost every ball game uses this principle.
• The speed can be maintained if the force is applied in a perpendicular angle but the velocity will change

#### FORCE CAN CAUSE A BODY TO DECELERATE

• If force is applied on the opposite direction of a moving object, it will decelerate or slow down and eventually stop altogether if the force is continued to be applied.
• For example, when a goalkeeper stops a ball, he causes it to decelerate and stop.