Build the energy model
Connect the kinetic energy of moving parts to rotational inertia and angular speed.
AP Physics 1 · Unit 6 · Energy and Momentum of Rotating Systems
Rotational Kinetic Energy
Watch spinning and rolling objects, track their energy stores, and predict motion using energy conservation and work done by torque.
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Learn by doing
Three ideas you’ll put into motion
Compare rolling motion
Change mass, radius, shape and friction on an incline, and follow the energy shared between translation and rotation.
Apply energy and work
Analyze a hinged rod and a driven turntable, then choose an angular velocity for a target energy.
The big idea
The key ideas, at a glance.
Rotation stores kinetic energy
About a fixed axis, rotational kinetic energy is Krot = ½Iω2. For rolling, add CM translational kinetic energy to rotational energy about CM.
Torque can transfer energy
A constant torque acting through an angular displacement does work W = τΔθ, with the angle in radians. Net work changes rotational kinetic energy.
A quick comparison
A disk rolls uphill with enough static friction to maintain no slip; an identical disk starts with the same speed and spin on a frictionless incline.
Compare the remaining spin and highest CM position.
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
- Translational kinetic energy, conservation of energy, rotational inertia, torque, radians and the no-slip condition.
- Built-in support
- Prepared scenes, guided prompts, and feedback on lesson questions.
- AP Physics 1 connections
- Unit 6: rotational kinetic energy and torque work (topics 6.1 and 6.2), connected to Unit 3 energy conservation.
- Check for understanding
- Ask why fixed-axle rotation can have energy with a stationary center, and why static friction need not dissipate mechanical energy.
Ready to test your thinking?
The first scene is set up. Start the lesson and explore.