Rocket adds a second washer to the bottom of the string. "Heavier must mean faster!" he says.
He swings it and counts. Ten swings. The same as before!
"What do you notice?" Raven asks. "The weight changed, but the count did not."
Nova hums. "Interesting," she says. "Try moving the weight up the string instead."
Scientists at a science museum tested this too.
Adding weight to the bottom of a pendulum did not change how fast it swung.
Making the pendulum shorter did change it. A shorter pendulum swings faster.
So the length of a pendulum sets its pattern.
This practice table uses made-up numbers. It shows the pattern scientists found.
| Practice table (made-up numbers) | Swings in 15 seconds |
|---|---|
| Long string, 1 washer | 10 |
| Long string, 2 washers | 10 |
| Short string, 1 washer | 14 |
| Change | Does it change the swing speed? |
|---|---|
| Make the string shorter | ? |
| Make the string longer | ? |
| Add a washer to the bottom | ? |
Rocket wanted to know if weight changes a swing. So he changed only the weight.
He kept the string the same length. He counted for the same 15 seconds.
If he had changed the length too, he could not tell which change mattered.
| Test plan | Is it a fair test of weight? |
|---|---|
| Same string length, add one washer | ? |
| Shorter string and one more washer | ? |
| Same string, same washer, count for 15 seconds | ? |
You thought like a real scientist today! Tomorrow we see how pendulums helped people tell time.