Modeling Prompt

Before class, prepare a demonstration pendulum using a washer and a piece of string.

Arrange students in groups of 2–4. Distribute to each group:

• 4 washers (or other appropriate objects) of differing weights
• string (at least 3 feet)
• scissors
• a stopwatch

A pendulum is a weight suspended from a pivot point so that it may freely swing. Demonstrate using your prepared sample pendulum. You can simply hold the top of the string between your fingers, or you could loop the string around a pencil a few times and hold the string against the top of the pencil, to allow the pendulum to swing more freely.

Ask, “Where have you seen pendulums before?” (clocks, swings, wrecking ball)

Tell students that a pendulum’s period is the time it takes for one full swing, back and forth. Demonstrate by pulling the weight back, letting the weight swing forward and back, and catching the weight. The time it takes for that to happen is the pendulum’s period.

Ask students what they think you could change about your pendulum that would change its period. Some possibilities are: the amount of weight at the end, the length of the string, or how far you pull the weight back before letting go. As students mention different potential variables, write these for all to see. Tell students that they will run experiments to figure out which of these variables affect the period.