AP Physics 1 ›  Unit 6

Unit 6 Energy & Momentum of Rotating Systems

Unit 5 taught you how rotation works. Unit 6 asks how much energy it carries, how much momentum it has, and what happens when systems spin up, slow down, roll, and orbit. Six episodes. Two conservation laws. One spinning universe.

📋 5–10% AP Exam Weighting🕐 ~16–22 Class Periods📺 6 Episodes✅ Progress Check 6
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Episode Guide — Season 6

EP.6.1

Rotational Kinetic Energy

A spinning object has kinetic energy even when its center of mass is stationary. K_rot = ½Iω² — the rotational twin of the familiar ½mv².

K_rot = ½I*omega²Total KE = K_cm + K_rotWork-energy theoremEnergy conservation
🕐 2–3 daysOpen →
EP.6.2

Torque and Work

Forces do work over linear displacements. Torques do work over angular displacements. W = τΔθ — the rotational work equation.

W = tau * DthetaPower = tau * omegaWork-energy theorem rotationalPositive and negative work
🕐 2–3 daysOpen →
EP.6.3

Angular Momentum and Angular Impulse

Linear momentum has a rotational counterpart. L = Iω is angular momentum — a conserved vector that resists changes in rotation.

L = I*omegaAngular impulse = tau*Dt = DLkg·m²/sVector quantity
🕐 3–4 daysOpen →
EP.6.4

Conservation of Angular Momentum

In an isolated system, total angular momentum never changes. The figure skater pulling their arms in — the most iconic physics demonstration in the unit.

L_i = L_fI_1*omega_1 = I_2*omega_2Isolated systemsSkater problem
🕐 3–4 daysOpen →
EP.6.5

Rolling

Rolling without slipping combines linear and rotational motion. Every point on the rim has both translational and rotational velocity — adding vectorially to give the observed motion.

v_cm = R*omegaK_total = ½mv² + ½Iω²No-slip conditionRolling down ramps
🕐 3–4 daysOpen →
EP.6.6

Motion of Orbiting Satellites

Gravity provides the centripetal force for circular orbits. Orbital speed, period, and energy all follow from Newton's Law of Universal Gravitation applied to circular motion.

F_g = GMm/r²v_orb = sqrt(GM/r)T² ∝ r³Orbital energy
🕐 3–4 daysOpen →
🎓 AP Classroom — Progress Check 6
Angular momentum conservation FRQs require explicit statements of system isolation, before/after diagrams, and algebraic solutions showing L_i = L_f.
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