class-9th Lesson -Force and Motion

1. Force And Laws Of Motion

2. FORCE
The push or pull on an object with mass that causes it to change its velocity. Force is an
external agent capable of changing the state of rest or motion of a particular body. It has a
magnitude and a direction.

4. Force can be used
*To change the magnitude of velocity of an object.
*To make the object move faster or slower.
*To change its direction of motion.
*To change the shape and size of the object.

6. Friction

11. Why should we wear seat belt while sitting in car?
 The cars are provided with seat belts for passengers to prevent injuries in case of an accident. In
an accident, the fast running car stops suddenly. Due to this the momentum of the car reduces
to zero in a very short time. The stretchable seat belts worn by the passengers increase the time
taken by the passengers to fall forward. Due to longer time, the rate of change of momentum is
reduced, and hence less stopping force acts on them. So, the passengers are saved from fatal
injuries.

14. Newton’s Second Law Of Motion
The second law of motion states that the rate of change of
momentum of an object is proportional to the applied
unbalanced force in the direction of force.

16. Momentum
Momentum is the product of mass and velocity of the object.
It is a vector quantity so it has magnitude as well as direction
SI unit of momentum is Kg m/s
P=mv

17. Third law of Motion
The third law of motion state that when one object exerts a force on
another object ,the second object instantaneously exerts a force back
on the first.
The two forces are always equal in magnitude and opposite in direction but these
forces do not produce acceleration of equal magnitude because each force act
on a different object that may have different mass

20. Third law of motion
 The third law of motion states that when one object exerts a force on another object ,the second
object instantaneously exerts a force back on the first.
 To every action there is an equal and opposite reaction.
 The action and reaction always act on two different objects.

23. Thanks for watching