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# Demonstration of a Pendulum

by Ron Kurtus (updated 9 January 2023)

The following animation is a demonstration of a pendulum in action. (Some browsers may not allow access to this Flash animation.)

Questions you may have include:

• What happens when you change the angle?
• What happens when you change the length of the string?
• What happens when damping occurs?

This lesson will answer those questions. Useful tool: Units Conversion

## Demonstration

The demonstration below shows a pendulum that starts at an angle of 30°. You can click the Start button to set it in motion.

## Change angle

By stopping the motion and entering another number in the Initial angle box, you can see that the period, rate of motion, or frequency does not change.

Try entering 20.

## Change length

You can also change the relative length of the pendulum to see how it changes the frequency. (The length in the demonstration does not actually change, but the frequency will change, as if the length actually did change according to what is entered in the Relative length box.)

Enter 2 to double the length. You can see the swing is slower.

Enter 0.5 to cut the length in half. (You must use decimals. Fractions won't work.) You can see the frequency of swing is faster.

## Damping

When a pendulum moves, there is some air resistance on the bob and rod or wire. There is also friction at the pivot point. These resistive forces reduce the amplitude of the swing, such that after a while the pendulum will come to a stop. These forces are called damping forces.

In the demonstration above, you may note that the amplitude of the swing gets smaller with time. There is a slight damping factor included in the simulation.

## Summary

A pendulum is a suspended weight that swings back and forth in a regular periodic motion. The length of the pendulum determines its frequency, while the weight of the bob does not affect the frequency. Pendulums have been used in clocks for hundreds of years, because the motion is so regular.

## Resources and references

Ron Kurtus' Credentials

### Websites

Simple Pendulum - Hyperphysics explanation

How Pendulum Clocks Work - From How Stuff Works

Pendulum Physlet - Java application and equations for a damped pendulum

The Foucault Pendulum - University of Louisville pendulum

Physics Resources

### Books

(Notice: The School for Champions may earn commissions from book purchases)

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www.school-for-champions.com/science/
pendulum_demonstration.htm

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