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# Force and Laws of Motion

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

## 01 Force and Motion

Motions of body around us like throwing a ball, hammering a nail, etc are based on the relationship between force and motion.

#### FORCE

• They are used in our everyday actions like pushing, pulling, lifting, stretching, twisting and pressing.
• It is a push or pull on an object that produces acceleration in the body on which it acts.
• Example:
• The force exerted by the engine makes the train to move from its actual position of rest while the force exerted by the brakes slows down or stops the moving train.
• If two bodies of mass and are kept in such a way that the body with mass is resting over the body with mass these two bodies will exert forces on each other. In other words, whenever there is an interaction of two or more bodies, force is a part of the interaction.

#### EFFECTS OF FORCE

A force cannot be seen. It can be judged only by the effects which it can produce in various bodies (or objects) around us.

• A force can move a stationary body.
• A force can stop a moving body.
• A force can change the speed of a moving body.
• A force can change the direction of a moving body.
• A force can change the shape (and size) of a body.

#### BALANCED AND UNBALANCED FORCES

Forces are of two types:

• Balanced forces
• Unbalanced forces.

Balanced forces: When the resultant of all forces acting on a body is zero, the forces are said to be ‘balanced forces’.

Unbalanced forces: When the resultant of the all forces acting on a body is not zero, the forces are said to be ‘unbalanced forces’.

#### RESULTANT FORCE

The resultant force is a single force obtained by combining several forces acting simultaneously on a body

#### MOTION

• Whenever a body is moving, it is said to be in motion.
• A boy walking down the street from his school to his home is in motion. But if the boy stops for minutes in the way and sits down he is not in motion. So, motion of a body is dependent on time
• Motion is the change in the position of a body with respect to time.

#### FRICTION

Whenever a body slides or rolls over the surface of another body, a force comes into action which acts in the opposite direction of the motion of a body. This opposing force is known as friction.