A.4.11 (HL)—Angular impulse

Angular impulse

A torque acting for a time changes angular momentum:

$\Delta L=\tau\Delta t=\Delta(I\omega)$

Area under a torque–time graph

If torque varies, the signed area under a $\tau$ -against-time graph gives angular impulse and therefore the change in angular momentum.

Common trap

Angular impulse has units N m s, not N s; keep it distinct from linear impulse.

How it is assessed

The evidence asks for the unit of angular impulse and for the physical quantity represented by the area under a torque–time graph.

Command terms

Identify

What earns marks

Identify angular impulse as the change in angular momentum. Use ΔL=τΔt for constant torque or the area under a torque–time graph; report units N m s.

Watch for

Choosing N s, the unit of linear impulse, instead of N m s for angular impulse.

Representative question

[Maximum number: 1]

What is the unit of angular impulse?

$\mathrm{Nms}^{-1}$

Nms

Calculate Angular Impulse