Momentum & impulse

Momentum is a quantity of motion defined by


measured in kilogram-metres per second (kg⋅m/s). A change in momentum is called impulse, and it is defined by


A lightweight, fast-moving object can have the same momentum as a heavy, slow-moving object because mass and velocity are multiplied. Similarly, a large force applied over a short time interval can deliver the same impulse as a small force applied over a long time interval.

Just as the area under an acceleration-time graph represents Δv, so too the area under a force-time graph represents Δp.


What average force is needed to stop a 34 kg ball in 2.5 s if the initial speed of the ball is 19 m/s [fwd]?

Since FΔt=mΔv,

F=mΔvΔt=v2v1Δt=(34 kg)(019 m/s)2.5 s=258.4 N,

therefore an average force of 260 N [bwd] is required.