AP Physics 1 / Topic
Torque and Rotational Dynamics
Unit 5 extends Newton's laws to rotation: torque, rotational equilibrium (beams, seesaws, ladders), rotational inertia, angular kinematics, and Newton's second law for rotation.
What the exam asks
- Compute torque including the angle and lever-arm dependence
- Solve static equilibrium problems where net force and net torque are both zero
- Compare rotational inertias from mass distribution (point masses, rods, disks, hoops)
- Apply angular kinematics for constant angular acceleration
- Use Στ = Iα, including pulleys with mass and Atwood-style machines
Key formulas and rules
τ = rF sinθ (r from pivot to where the force acts)
ΣF = 0 and Στ = 0 about ANY pivot point
I = Σmr²; mass farther from axis ⇒ larger I
Στ = Iα
ω = ω0 + αt; θ = ω0t + ½αt²; linear links: v = rω, a = rα
Question bank breakdown
39
3
11 easy · 22 medium · 6 hard
Skills covered
Every question in the bank comes with a worked explanation, and most add a per-choice breakdown so you learn why each wrong answer is wrong - not just the key.
Sample question
From the free tier of the ScoreMint AP Physics 1 bank - try it, then check the answer.
A wheel starts from rest and accelerates uniformly at for . How many complete revolutions does the wheel make during this time?
- A. revolutions
- B. revolutions
- C. revolutions
- D. revolutions
Show answer and explanation
Answer: B. This problem applies rotational kinematics, which parallels linear kinematics. Starting from rest (), the angular displacement is rad. To convert radians to revolutions, divide by : revolutions. The rotational kinematic equations have the same form as their linear counterparts: , , .
Study tip
In beam problems, put the pivot at the point where an unknown force acts - that force's torque vanishes and the equation solves itself with one unknown.