College Board-Aligned Original Notes

AP Physics C: Mechanics Unit 7 Topic 2: Pendulums

Pendulum motion is modeled as simple harmonic motion when the angle is small.

Unit 7: Oscillations. College Board exam weighting listed for this unit: 10%-15% of multiple-choice score.

What to Know

For small angles, a simple pendulum's restoring torque produces approximately simple harmonic motion.
The period of a simple pendulum depends on length and gravitational field strength in the ideal model.
Large amplitudes, air resistance, and pivot friction make the ideal model less accurate.
Always connect this topic back to the larger unit: Oscillations.

Detailed Notes

Pendulums belongs to Unit 7: Oscillations. Pendulum motion is modeled as simple harmonic motion when the angle is small. In AP Physics C: Mechanics, the explanation should connect diagrams, calculus relationships, and the physical meaning of each quantity.

Key relationships: For small angles, a simple pendulum's restoring torque produces approximately simple harmonic motion. The period of a simple pendulum depends on length and gravitational field strength in the ideal model. Large amplitudes, air resistance, and pivot friction make the ideal model less accurate.

Model to use: Draw the pendulum bob, tension, weight components, and the tangential restoring component. Define the coordinate system, system boundary, and sign convention before writing equations.

AP-style move: Use the small-angle approximation only when the problem supports it. Show the setup symbolically, then interpret the answer with units and direction when relevant.

Key Vocabulary

Simple pendulum

A point mass suspended by a light string in an ideal pendulum model.

Small-angle approximation

The approximation that sine of theta is about theta in radians for small theta.

Pendulum restoring torque

Torque that pulls the pendulum back toward equilibrium.

Pendulum period

Time for one complete swing cycle.

Angular displacement

The angle of the pendulum from equilibrium.

Quick Practice

How would you explain Pendulums in one or two AP-style sentences?

Name the concept, apply it to a specific example or source, and explain the reasoning that connects the evidence to your answer.

Official Alignment

Reference and Attribution

AP Physics C: Mechanics concept reference: AP Physics C Mechanics-Concise Summary Notes by IITian Academy. EduCompanion used this source as a topic checklist and conceptual reference, then rewrote the study notes in original wording.

AP Physics C Mechanics-Concise Summary Notes