Concept preview

What you will be able to do

1. 01Define impulse as $J = F\Delta t$ and relate it to the change in momentum
2. 02Use the area under a force–time graph to find impulse
3. 03Explain safety devices in terms of extending the collision time

We saw that a force changes momentum. Impulse measures the total change a force delivers by combining how hard it pushes with how long it pushes: $\vec{J} = \vec{F}\,\Delta t$, in units of $\text{N}\cdot\text{s}$. Rearranging Newton's second law, $\vec{F} = \Delta\vec{p}/\Delta t$, gives the impulse–momentum theorem: $\vec{J} = \vec{F}\,\Delta t = \Delta \vec{p}$. Impulse is the change in momentum — same size, same units ($\text{N}\cdot\text{s} = \text{kg}\cdot\text{m/s}$).