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The Pendulum

Part of the Mechanics section of Coddy's Physics journey. Lesson 80 of 94.

Pull a pendulum aside and the part of the weight along its path pulls it back toward the lowest point.

A pendulum of length L hanging from a pivot, pulled aside by the angle theta from the vertical; the tension T pulls along the string, the weight mg pulls down, and the part of the weight along the path, mg sin theta, points back toward the lowest point

The part of the weight along the path, mg sin θ, pulls the bob back toward the middle.

For small swings, up to about 15°:

T = 2π √(L/g)

The mass of the bob is not in it.

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Challenge

An astronaut on the Moon swings a pendulum 0.4 m long and measures a period of π s, about 3.1416 s. Find the Moon's g.

Try it yourself

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This lesson includes a short quiz. Start the lesson to answer it and track your progress.

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