Class 9 Science notes ch 1 Laws of motion Maharashtra State Board

 

1. Laws of Motion notes

                                           Class 9 Science

If the position of an object is changing with respect to its surroundings, then it is said to be in motion. Otherwise, it is said to be at rest.

 

Distance : Actual path travelled by the body or total length covered by body is called distance.

 

Displacement : Shortest distance between two point is called the Displacement.

 

·      Distance cannot be zero or negative.

·      Displacement may be zero , positive and negative.

 

Speed : rate of change of distance w.r.t. time is called speed.

Speed is related to distance.

Its unit is m/s

 

Velocity : Rate of change of displacement w.r.t. time is called velocity.

Velocity is related displacement.

Its unit is m/s

 

Effect of speed and direction on velocity

If the speed changes or velocity changes or both quantity changes then velocity also change.

 

Uniform speed: If an object covers equal distances in equal time intervals, it is said to be moving with uniform speed.

 

Non uniform speed: If an object covers unequal distances in equal time intervals, it is said to be moving with non-uniform speed.

For example, the motion of a vehicle being driven througth heavy traffic.

 

Acceleration:

If the velocity of an object changes during a certain time period, then it is said to have accelerated motion. An object in motion can have two types of acceleration.

1. If the velocity changes by equal amounts in equal time intervals, the object is said to be in uniform acceleration.

2. If the velocity changes by unequal amounts in equal time intervals, the object is says to be non-uniform acceleration.

 

When the velocity of an object increases, the acceleration is positive. In this case, the acceleration is in the direction of velocity. When the velocity of an object decreases with time, it has negative acceleration. Negative acceleration is also called deceleration. Its direction is opposite to the direction of velocity. If the velocity of the object does not change with time, it has zero acceleration.

Graph shows straight for Uniform motion.

 

Uniform circular motion

If the object following circular path with constant speed then  such motion is called uniform circular motion.

If object travelling along the circular path with constant speed then its velocity always change due change in direction of object.

 

Newton’s laws of motion

Newton’s first law : An object continues to remain at rest or in a state of uniform motion along a straight line unless an external unbalanced force acts on it.’

 

Newton’s second law: ‘The rate of change of momentum is proportional to the applied force and the change of momentum occurs in the direction of the force.’

 

Newton’s third law: ‘Every action force has an equal and opposite reaction force which acts simultaneously.’

 

Momentum : Momentum is product of mass and velocity.

 

Law of conservation of momentum

 

The magnitude of total final momentum = the magnitude of total initial momentum.

 

‘When no external force acts on two interacting objects, their total momentum remains constant. It does not change.’

 

‘When two objects collide, the total momentum before collision is equal to the total momentum after collision.’

Download PDF

 

Thank you

8657332280