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"Impulse" and "Change in momentum"

Can someone please clarify for me the difference between Impulse and the Change in momentum? I thought they were the same up til now, until I came across a load of questions where they asked me to work out both,
Eg

A boy catches a 150 gram cricket ball travelling towards him at 20ms-1.
Calculate:

a) The decrease in momentum of the ball
b) the impulse acting on the ball
c) the average force exerted by the boy if the catch takes 0.1 seconds.
As far as I know, they are the same. In a practice exam I did it asked you calculate the change in momentum, but state the impulse.
Reply 2
Avatar for marcusfox
marcusfox
16
In the technical sense, impulse is a physical quantity, not an event or force. However, the term "impulse" is also used to refer to a fast-acting force. This type of impulse is often idealized so that the change in momentum produced by the force happens with no change in time. This sort of change is a step change, and is not physically possible. However, this is a useful model for certain purposes, such as computing the effects of ideal collisions, as in your above problem.

Impulse has the same units and dimensions as momentum (kg m/s = N·s).
Reply 3
Avatar for turgon
turgon
OP
11
When you say STATE the impulse what would be different from the change in momentum you calculated? :confused: The only thing I can think of is that in impulse the units Ns are more commonly used, as opposed to kgms-1. Also, if the change in momentum is negative, would impulse be negative as well seeing as its a vector quantity?
Reply 4
Avatar for turgon
turgon
OP
11
I think I get it now,:smile: thanks for that

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