Practice rotational kinematics, torque, rotational inertia, and angular acceleration. Quiz one topic at a time or take the whole unit.
The idea each topic turns on, and the mistake students make most often.
Key ideaRotational kinematics mirrors linear kinematics: θ, ω and α play the roles of x, v and a, in the same equations (for constant α).
Common mistakeMixing degrees or revolutions into equations that require radians.
Key ideaAt a distance r from the axis, v = rω and the tangential acceleration is rα. Every point on a rigid object has the same ω.
Common mistakeThinking points farther out have a larger ω. They have a larger linear speed, but the same ω.
Key ideaTorque is the force times the lever arm, the perpendicular distance from the axis to the force’s line of action: τ = rF sin θ.
Common mistakeUsing the full distance r when the force is not perpendicular, or forgetting that a force through the axis produces no torque.
Key ideaRotational inertia depends on how the mass is distributed: the farther the mass is from the axis, the larger I is.
Common mistakeThinking two objects with equal mass have equal rotational inertia, or forgetting that I depends on where the axis is.
Key ideaThe net torque equals the rotational inertia times the angular acceleration: Στ = Iα.
Common mistakeUsing force instead of torque, or leaving out a torque such as friction at the axle.
This is one of the 23 questions in the Unit 5 quiz.
What does angular displacement describe?
Answer: A. The angle through which an object has rotated
Angular displacement θ indicates the angle through which an object has rotated. It is measured in radians.
AP-style FRQs for this unit. Students score themselves point by point against a rubric and see a full solution.
