AP Physics 1 · Unit 6 · Energy and Momentum of Rotating Systems

Angular Momentum

Compare spinning and straight-line motion about a reference point, then use torque acting over time to predict changes in angular momentum.

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Learn by doing

Three ideas you’ll put into motion

Connect particle angular momentum to mass, speed and perpendicular distance from a stated point.

Relate angular momentum to rotational inertia and angular velocity, including clockwise and counterclockwise signs.

Interpret graph slopes and areas, solve soccer-ball and door examples, and set a torque for a target final angular momentum.

The big idea

A rigid rotor has L = Iω about the stated axis. A point mass has magnitude |L| = rmv sin θ, or mvd for perpendicular distance d to a straight path.

Angular impulse equals ΔL. For constant net torque, τΔt = ΔL; more generally, use the area under the curve of the net torque–time graph.

A quick comparison

Apply the same net torque to the same rotor for a longer time, with the same initial state.

Compare the change in angular momentum with the torque–time area.

Teaching this topic?Classroom fit, AP connections, and support

Classroom fit: Use for a concept introduction, guided independent practice, or a projected class discussion.
Before students begin: Linear momentum, rotational inertia, angular velocity, torque, radians and basic graph interpretation.
Built-in support: Prepared scenes, guided prompts, and feedback on lesson questions.
AP Physics 1 connections: Unit 6: angular momentum and angular impulse (topic 6.3, objectives A, B and C).
Check for understanding: Ask why a straight-moving object can have nonzero angular momentum about a point away from its path, and why equal impulses need not give equal angular-velocity changes.

The first scene is set up. Start the lesson and explore.