AP Physics 1 / Topic
Energy and Momentum of Rotating Systems
Unit 6 covers rotational kinetic energy, rolling without slipping, angular momentum, and its conservation — including collisions that make things spin and the classic spinning-skater scenario.
What the exam asks
- Split the kinetic energy of rolling objects into translational and rotational parts
- Race rolling shapes down inclines using energy partition arguments
- Apply the rolling constraint linking v and ω
- Compute angular momentum for spinning objects and moving point masses
- Use conservation of angular momentum when net external torque is zero (skaters, rotational collisions)
Key formulas and rules
KE(rot) = ½Iω²; rolling total: ½mv² + ½Iω²
v = rω (no slipping)
smaller I/(mr²) reaches the bottom first (sphere beats disk beats hoop)
L = Iω; point mass: L = mvr (perpendicular distance)
no external torque ⇒ I1ω1 = I2ω2 (arms pulled in ⇒ spin faster)
Question bank breakdown
47
3
10 easy · 26 medium · 11 hard
Skills covered
Every question in the bank comes with a per-choice explanation, so you learn why each wrong answer is wrong — not just the key.
Practice this topic
The full set of Energy and Momentum of Rotating Systems questions — with a per-choice explanation on every answer — lives in the practice workspace. Start free, no account needed.
Study tip
When a mass sticks to a rotating rod or disk, conserve angular momentum, never linear momentum or energy — the axle supplies external forces but no torque about itself.