# Impulse

When you throw a Javelin or a ball you should start with your arm well behind you.
When you jump onto a concrete floor it hurts more than jumping into a sand pit.
When you catch a cricket ball or a rounders ball you should let your hands give.
Playing cricket with an iron cricket bat would be very painful.
You can’t jump at all without bending your knees first.
When you hit a ball you should “follow through” with your stroke

If an unbalanced force acts on an object its velocity will change. We must now find out how this change can be made bigger and see what affects how fast an object can be made to move.

A javelin thrower is a good example of a force (arm muscles) being used to make an object (the javelin) move off as fast as possible.

The bigger the force that the thrower uses the faster the javelin will go. But why are you told to throw the javelin from behind you? This is so that the force in your arm is pulling on the javelin for the longest possible time.

The change in velocity depends on both the force and the time for which it acts.

We call the product of force and time the IMPULSE. The bigger the impulse the bigger the change in velocity it will produce.

Impulse = force x time = Ft

The units of impulse are Newton seconds (Ns).

The same arguments apply when you catch something. The less time you take to catch it the bigger the force and so the more it hurts.

A VERSION IN WORD IS AVAILABLE ON THE SCHOOLPHYSICS CD