Explicit physics instruction
External torque changes angular momentum over time. The rotational impulse relation parallels linear impulse.
A larger torque or longer torque interval produces a larger ΔL.
Internal torques can redistribute angular momentum within a system without changing its total.
Core relation: L=Iω and ΔL=τ_extΔt.
Worked example
A net external torque of 3 N·m acting for 2 s changes angular momentum by 6 kg·m²/s.
Guided question
How is angular impulse related to torque-time area?
Independent work
- Solve three angular-momentum or torque-time problems.
- Declare the system and external-torque assumption.
- Record one unit/assumption check.
Misconception check
Conserved angular momentum does not mean angular speed is constant; I can change.
Formative check
If I is halved with L conserved, what happens to ω?
Reveal response
It doubles.
Mentor evidence conference
Ask Archaemenes to audit the system boundary, moment-of-inertia reasoning, and external-torque claim.
Teacher guidance
Foundation: Compute L=Iω.
Core: Solve conservation and torque-time changes.
Extended: Evaluate conservation residuals with uncertainty.