Impulse and force–time graphs · Grade 9
Impulse is the effect of a force acting for a time: force × time. It equals the change in momentum. Spreading a change in momentum over a longer time means a smaller force, which is the idea behind airbags, crumple zones, crash mats and bending your knees when you land.
Key facts
- Impulse = force × time = FΔt (N s).
- Impulse = change in momentum: FΔt = mv − mu. (1 N s = 1 kg m/s.)
- Force = rate of change of momentum: F = (Δp)/(Δt).
- For the same change in momentum, a longer contact time gives a smaller force.
- Impulse = area under a force–time graph.
- Rebounds: the velocity reverses, so the change in velocity is u + v.