FORCEA PUSH OR PULL ON A BODY IS CALLED FORCE.FORCES ARE USED IN OUR EVERYDAY ACTIONS LIKE PUSHING, PULLING, LIFTING, STRECHING, TWISTING AND PRESSING.

EFFECTS OF FORCE

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

1.A force can move a stationary body.2.A force can stop a moving body.3.A force can change the speed of a moving

body.4.A force can change the direction of a

moving body.5.A force can change the shape and size of a

body.

BALANCED AND UNBALANCED FORCE

• THERE ARE TWO KINDS OF FORCE:• 1. BALANCED FORCE.• 2. UNBALANCED FORCE.

BALANCED FORCESIf the resultant of all the forces acting on a body is zero, the forces are called balanced forces.If a number of balanced forces act on a stationary body, the body continuous to remain in its stationary position.If a number of balanced forces act on a body in uniform motion, the body continuous to be in its state of uniform motion.Though balanced forces cannot produce motion in a stationary body but can change the shape of the body.

UNBALANCED FORCE

If the resultant of all the forces acting on a body is not zero, the forces are called unbalanced forces.When an unbalanced force acts on a body, it produces motion in the body. Also, an unbalanced can stop a moving body.If there were no unbalanced force of friction or air resistance, a moving body would go on for ever.

NEWTON’S LAW OF MOTION

• NEWTON HAS GIVEN THREE LAWS OF TO DEFINE THE MOTION OF BODIES. THESE LAWS ARE KNOWN AS NEWTON’S LAWS OF MOTION.

NEWTON’S FIRST LAW OF MOTIONA body at rest will remain in rest, and a body in motion will continue in motion in a straight line with uniform speed, unless it is compelled by an external force to change its state of rest or of uniform motion.

INERTIA: Inertia is that property of a body due to which it resists a change in its state of rest or of uniform motion.

MOMENTUMThe momentum of a body is defined as the product of its mass and velocity.NOTE: the force required to stop a moving body is directly proportional to its mass and velocity.Thus, momentum= mass x velocity or, p= m x v where p= momentum m= mass of the body and, v = speed of the body

SI UNIT= the SI unit of momentum is kilogram meters per second (kg.m/s)

NEWTON’S SECOND LAW OF MOTION

The rate of change of momentum of a body is directly proportional to applied force, and takes place in the direction in which force acts.Force= change in momentum/time taken f= mv-mu/tf= m(v-u)/t. But we know that v-u/t =a f= m x a force = mass x accelerationSI UNIT: its SI unit is ‘force’.

NEWTON’S THIRD LAW OF MOTION

Whenever one body exerts a force on another body, the second body exerts equal and opposite force to the first body. OR, To every action there is equal and opposite reaction.1.EX: the rocket works on the principal of action and reaction.2.When a bullet is fired from the gun, a force sending the bullet forward is equal to the force sending the gun backward. But due to high mass of the gun, it moves only a little distance backward and gives jerk.

CONSERVATION OF MOMENTUM

When two or more bodies act upon one another, their total momentum remains constant provided no external forces are acting.Momentum is neither created nor destroyed.

Total momentum before collision = total momentum after collision

THE ENDMADE BY: ASHUTOSH KUMARCLASS:9TH ‘C’ARMY PUBLIC SCHOOL, RANIKHET