Impulse and Momentum
Momentum
The momentum of an object is the product of its mass and its velocity. Momentum is a vector quantity and is measured in Ns or \cfrac { kgm }{ s }
The equation for momentum is:
p=mv
p = momentum in \cfrac { kgm }{ s }
m = mass in kg
v= velocity in \cfrac { m }{ s }
Impulse
A change of momentum is known as an impulse. When a force acts on an object to change its velocity, the momentum of the object will change because the velocity changes. The equations for impulse are:
I=\Delta p={ p }_{ f }-{ p }_{ i }
\Delta p=mv-mu=m(v-u)
Another equation for impulse is:
I=Ft
Example 1:
What is the momentum of a 50kg girl walking north at 2.5\cfrac { m }{ s } ?
p=mv
p=50\times 2.5
p=125\cfrac { kgm }{ s } north
Example 2:
A 900kg car is travelling west at 8.2\cfrac { m }{ s } before coming to a complete stop at a red light. What is the impulse of the car as it stops at the red light?
I=\Delta p={ p }_{ f }-{ p }_{ i }
\Delta p=mv-mu=m(v-u). Note: we will denote west as positive:
\Delta p=900(0-8.2)
\Delta p=-7380
Therefore, Impulse=7380\cfrac { kgm }{ s } east