Impulse

Impulse is the change in momentum. Because impulse is the change in momentum, its symbol is a P, which stands for momentum, and a ∆ which indicates change. So ∆P represents impulse. The equation for change in momentum is: Fnet*∆T = ∆P. It can also be represented by P(o) - P.

If two objects, a rubber ball and a box, are thrown at a wall, the rubber ball will undergo a greater change in momentum than the box will. This is because the ball bounces back while the box hugs the wall and slides down. The ball bounces back towards the thrower this indicates the ball now has negative momentum. Suppose the ball, which bounces back the same speed in the opposite direction, and box are both 1 kg while the velocities are both 5 m/s to the right. The original momentum of the box is 1kg*5m/s =  5Ns. The final momentum of the box is 0Ns. The original momentum of the ball is 1kg*5kg = 5Ns. The final momentum is 1kg*-5m/s = -5Ns. Therefore, the impulse of the box is 5Ns - 0 = 5Ns, while the impulse of the ball is -5Ns - 5Ns = -10Ns.


Another thing to note: the longer the change in time is, the longer force can be applied at a low rate, as opposed to a short change in time with high force. The former is less painful than the latter. That is why it is better to land on a mattress than it is to land on cement when you jump off a high platform. (The picture is of my soft mattress that would probably not save anyone if they jumped off a high building, but would still reduce the impulse by at least a little bit.)