FORCE AND LAW OF MOTION

                   CLASS 9

                   PHYSICS 

                  CHAPTER-2

 ➽  FORCE  AND LAW OF MOTION

 WHAT IS FORCE  ?

    A puss and pull on a body is called force.

    Unit of force is Newton (N).

  Effect of force:

1    .    A force can move a stationary body.

2    .    A force can stop a moving body.

3    .    A force can change speed of a moving body.

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

5    .    A force can change shape or size of body.

  BALANCED AND UNBALANCED FORCE

·      ➧    If the resultant of all the forces acting on the body is zero, the force are     called balance force.

·      ➧     If the resultant of all the forces acting on the body is not zero, the  force   are called unbalance force.

 Unbalance force can move a stationary body or they can stop a moving     body.

NEWTONS LAW OF MOTION

    NEWTONS FIRST LAW OF MOTION {Galileo law of inertia}

·        ➧ A body at a rest will remain at rest, and  a body in a motion will continue   in a motion in a straight line with a uniform speed, unless it is compelled   by external force to  change it state of rest.                                                                    ⇒

NEWTONS SECOND LAW OF MOTION

·         ➧ The rate of change of momentum of a body is directly proportional to the    applied force, and takes place in the direction in which the forceact.   {force= mass * acceleration }

      Applications of Newtons second law of motion

1       ➧ Catching a cricket ball.                  ⇉

        ➧ The case of high jumper.

           ➧ The use of seat belts in cars.

NEWTONS THIRD LAW OF MOTION

·         ➧ Whenever one body exerts a force on another body, the second body   exerts an equal and opposite force on the first body.

example

1.    The flying of jet Aeroplanes and Rockets.⇉

2.    The case of a boat and the ship.

3.    In case of horse pulling a cart. 

MOMENTUM 

·         ➧ The momentum of a body is defined as the product of its mass and         velocity.

·       ➧ Momentum= mass * velocity {p= m v}

·         ➧ If a body is at rest, its velocity is zero and hence its momentum is also       zero.

·         ➧ Momentum Is vector quantity.

·         ➧ Si unit is kg.m/s. {kg.ms^-1}

Conservation of momentum

    ➺  Momentum= mass * velocity

·        ➧ When two bodies act upon one another, their total momentum remain           constant provided on the external forces are acting.

·       ➧ m₁v₁₌m₂v_2.