Choose the axis and mass model
Use L = Iω for rigid rotation and r × p for a particle about a fixed point. Retain both stick and package contributions when an axle changes position.
AP Physics 1 · Unit 6 · Rotating Systems
Angular Momentum Practice Problems
Choose a reference axis, calculate spin or particle angular momentum, and measure how torque changes it. Compare rotating shapes, reel startup, central gravity, two masses on a bar, and a stick with an attached package; finish with a torque–time pulse that reverses rotation.
12 questions6 conceptual · 6 calculation
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What you’ll practice
Distinguish angular momentum from a change in angular momentum
Connect forces, torques, and constraints
Explain how a central force can change velocity without changing angular momentum, why a through-center force need not cause spin, and which reel assumptions determine torque and startup tension.
Read angular impulse from torque–time data
Use the area under the curve to find the change in angular momentum. Include an initial signed angular momentum before solving for final angular velocity and a possible reversal.
A question from this set
Spin direction and angular momentum
Two identical rigid rotors turn about the same kind of central axle at equal angular speeds, one counterclockwise and the other clockwise. With counterclockwise positive, how do their angular momenta compare?
Try it in the practice setKey ideas
Angular momentum depends on the chosen reference
A nonzero force can have zero moment about a point
Central gravity is directed toward its reference source, giving zero torque about that source. A force-free particle can also have nonzero angular momentum about a point away from its straight path.
Torque changes angular momentum through time
Net torque is the rate of change of angular momentum. A positive angular impulse can slow an initially clockwise rotor, bring it momentarily to rest, and then reverse its rotation.
See the physics
Compare measured momentum changes with angular impulse
After attempting the questions, inspect torque, angular momentum, and accumulated angular impulse from the running models. Compare reel snapshots, circular and eccentric central-force motion, axle choices, and the particle’s reference point. The triangular pulse supplies the actual torque that reverses the rotor.
Use a hint for a starting point or open a worked solution to follow the reasoning. Your progress saves in this browser, so you can return to unfinished questions.
Ready for angular momentum?
Begin with a conceptual question, then work through the calculations.