Tutoring physics, you get asked about impulse now and again.  The tutor introduces the topic, explaining its connection with momentum.

Impulse has many definitions.  Fundamentally, it means change in momentum.  Momentum is a vector quantity, which means it has a direction as well as a magnitude.  Impulse, being the change in momentum, is a vector as well.

A formula definition for impulse is

I=Ft

where I=impulse, F=force, and t=time.

Generally, impulse is thought to mean a large force being applied over a very short time duration. A club hitting a golf ball is such a situation.

Example: A golf ball of mass 80.0g is struck by a golf club with a force of 90.0N. The duration of contact is 120.ms. Find

b) the velocity of the golf ball after being struck.

Solution:

a) the impulse is given by I=Ft. The time is 120.ms, where ms means milliseconds. Therefore, the time is 0.120s.

I=(90.0)(0.120)=10.8kgm/s

So the impulse is 10.8kgm/s. Note that the unit of impulse is the same as momentum: Newtons times seconds (Ns), which equates to kgm/s.

b) the velocity of the golf ball can be found using the momentum formula

p=mv

Here, p (strangely, but universally) stands for momentum,m for mass, and v for velocity.

Assuming the golf ball is at rest before it was struck, the impulse applied to it becomes its momentum, since its momentum was zero before. Therefore, its momentum after being struck is 10.8kgm/s. From there, we can find the velocity using p=mv, as follows:

10.8=0.0800v

Note that the mass, being 80.0g, is 0.0800kg. You need base units – i.e., kilograms, metres, and seconds – in the momentum and impulse formulas.

We arrive at

10.8/0.0800=135=v

So, the golf ball’s velocity is 135m/s as it leaves. In real life, air friction quickly takes effect, giving the ball the graceful arc golfers know.

I’ve never been golfing myself:)

Jack of Oracle Tutoring by Jack and Diane, Campbell River, BC.