Pendulum simulator

What this simulator shows

A pendulum is a weight, called a bob, hanging on a string from a fixed point. Set the length from 0.1 m to 2 m, choose a bob of 50 to 500 grams, and drag the bob or use the buttons to set a starting angle from 5° to 60°. Press Let go and the simulator times 10 full swings, one swing meaning over and back again, then adds a row to the results table. A 4× speed button saves waiting for long pendulums; the times recorded are still real seconds.

• The length is what sets the swing time. A longer pendulum swings more slowly.
• Mass makes no difference: the 50 g and 500 g bobs take the same time.
• For small angles, the start angle hardly matters. At big angles, the swing takes a little longer.
• To double the swing time, you need four times the length. A 1 m pendulum takes about 2 seconds per swing.

Why it makes a great investigation

The pendulum is a classic fair test. There are three things you could change, and only one of them matters much, so children must change one thing at a time and keep the others the same to find out which. Timing 10 swings and dividing by 10 is the same trick scientists use to make a measurement more accurate.

Common misconceptions

Almost everyone predicts that a heavier bob will swing faster. It doesn't, for the same reason a heavy ball and a light ball fall at the same rate when air resistance is small. Many also expect a bigger push or a higher starting angle to make each swing quicker. The bob does move faster, but it has farther to go, so the time is nearly the same. A third mix-up is changing two things at once and then not knowing which one made the difference.

Some books count one swing as one way only. This simulator counts there and back. The model leaves out air resistance, so its pendulum never slows down.

A 10-minute pendulum activity

• Ask: "What do you think changes how fast a pendulum swings?" List the ideas.
• Time 10 swings at 1 m, 100 g, 20°. Then change only the mass and time again.
• Change only the length to 0.25 m and time again. Compare the three rows.
• Change only the angle to 50° and time again.
• Ask the child to write one sentence for each variable saying what it did.

Where this fits in school

• US, grades 4 to 8: pendulum investigations are a common way to practice planning and carrying out fair tests, one of the science practices in the NGSS.
• England, upper Key Stage 2: pendulums are a popular investigation for working scientifically, especially recognizing and controlling variables.
• England, Key Stage 3: pupils plan investigations, take repeat readings and look for patterns in data tables like this one.

Learning more

Eurekami's skill map includes science investigation skills as well as facts. Lessons model how to plan a fair test, and the AI tutor helps students read their own data tables with questions rather than answers.