Key Concepts: Impulse

What is Impulse?

• Impulse is the product of force and the time it acts: J = FΔt.
• SI unit: N·s = kg·m/s (same as momentum).
• Impulse equals the change in momentum: J = Δp = mv_f − mv_i.

Impulse-Momentum Theorem

FΔt = Δp

• A large force over a short time produces the same momentum change as a small force over a long time.
• For variable force: impulse = area under the F-t graph.

Applications

• Car airbags: Extend the collision time → reduce the force on the passenger.
• Catching a ball: Moving your hand back extends contact time → less force on your hand.
• Crumple zones: Car structures designed to deform slowly, increasing Δt and reducing F.