Class 9 Science

# MOMENTUM

Momentum is the power of motion of an object.

The product of velocity and mass is called the momentum. Momentum is denoted by ‘p’.

Therefore, momentum of the object = Mass × Velocity.

Or, p = m × v

Where, p = momentum, m = mass of the object and v = velocity of the object.

Consider the following explanations to understand the momentum:

A person gets injured in the case of getting hit by a moving object, such as stone, pebbles or anything because of momentum of the object.

Even a small bullet is able to kill a person when it is fired from a gun becasue of its momentum due to great velocity.

A person gets injured severely when hit by a moving vehicles, becasue of momentum of vehicle due to mass and velocity.

## Momentum and Mass and Velocity:

Since, momentum is the product of mass and velocity (p = m × v) of an object. This means momentum is directly proportional to mass and velocity.Momentum increases with increase of either mass or velocity of an object.

This means if a lighter and a heavier object is moving with same velocity, then heavier object will have more momentum than lighter one.

If a small object is moving with great velocity, it has tremendous momentum. And because of momentum, it can harm an object more severely. For example a small bullet having a little mass even kills a person when it is fired from a gun.

Usually, road accidents prove more fatal because of high speed than at slower speed. This happens because vehicles running with high speed have greater momentum compare to a vehicle running with slower speed.

### Momentum of an object which is in the state of rest:

Let an object with mass 'm' is in the rest.

Since, object is in rest, therefore, it's velocity, v = 0

Now, we know that,

Momentum = mass × velocity

Or, p = m × 0 = 0

Thus, the momentum of an object in the rest, i.e. non-moving,is equal to zero.

## Unit of momentum:

The SI unit of mass = kg

The SI unit of velocity = meter per second i.e. m/s

We know that, momentum (p) = m × v

Therefore,

p = kg × m/s

Or, p = kg m/s

Therefore, SI unit of momentum = kg m/s

### Think About These Points

A rubber ball and a cricket ball are moving at the same speed. Which of them is going to hurt more if you are hit by either of them?

You have to make a choice while driving on the road. You observe a road roller and a bicycle heading towards you. Which of these you will prefer to collide with head on? Why?

If all the planets in the Solar System are moving at the same speed, then which planet is going to have the greatest momentum? Why?