Impulse

The impulse $\relax J$ is the net force times the time it acts. It equals the change in momentum:

$$J = F\Delta t = \Delta p$$

Its unit is N·s, the same as kg·m/s.

The same change in momentum can come from a large force over a short time or a small force over a long time: a crash mat makes the stop last longer, so the force is smaller.

The area under each graph is the impulse: 800 · 0.1 = 200 · 0.4 = $80\ \mathrm{N\cdot s}$.