Impulse and momentum

Impulse and momentum are closely related as we shall see in this lesson. Recall that momentum = m × v,  where m is the mass and v is the velocity.  

In order to change the momentum of an object, we can either change the mass or the velocity.

If we don't change the mass, we will need to change the velocity to change the momentum.

Whenever there is a change in velocity, there is acceleration. Acceleration does not happen by itself. We know that force produces acceleration.

The greater the force applied to the object, the greater the acceleration, and hence the greater the change in momentum.

So far, we see that force is important to change the momentum of an object.

There is something else that can change momentum. Which situation do you think have more momentum?

Situation 1 :  A force is applied for 60 seconds.

Situation 2:   A force is applied for 20 seconds 

The more an object moves, the more momentum the object has. Since in situation 1 the object is in motion for a longer period of time, it will have more momentum.

Thus, to change the momentum both the force and the time are important.

We can now define what impulse is in physics. Simply put, impulse is the quantity force × time.

We can write this as an equation as shown below.

Impulse  = F × t

Impulse = Ft

F is measured in Newtons and t in second.

The unit of impulse is N.s

Difference between impulse and momentum

Impulse and momentum are not exactly the same. Momentum is just the fact that an object is in motion. Impulse on the other hand can create a change in momentum. The greater the impulse, the greater the change in momentum.

Impulse and momentum relationship

Impulse = change in momentum

Ft = ▲(mv)


The impulse does not only refer to increasing the momentum of an object. It can also refer to decreasing the momentum of an object all the way to a momentum that is equal to zero.

Whether you fall on a mattress or a concrete, your momentum will equal to zero when you hit the mattress or the concrete.

Your momentum though is still decreased by the same impulse.

Impulse on concrete vs mattress

When you hit the mattress, the force of impact is reduced as you increase the impact time or the time your momentum is brought to zero.

On the other hand, the concrete floor will stop you abruptly. In other words, the impact time is very short. As a result, the force of impact is more severe.

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