Lesson 3 of 16
A swing that keeps time
Show on a big screenA key hangs on a thread. You let it swing. Each swing takes almost the same time.
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The idea
A pendulum is a small ball, the bob, hanging on a thread. One oscillation is one full to-and-fro swing. Start at one end. Go across to the other end. Come back to the start.
The time period is the time for one oscillation.
To find the time period, time 10 oscillations. Then divide the time by 10. One oscillation is too quick to time well. For example, 10 oscillations take 20 s. So the time period is 20 ÷ 10 = 2 s.
The time period depends on the thread length. The bob's mass, how heavy it is, does not matter.
Step 1 of 4
- A bob hangs on a 100 cm thread.
- It swings. 10 oscillations take about 20 s.
- A 25 cm thread: 10 oscillations take about 10 s.
- A heavier bob: still about 10 s.
Try the lab to finish this lesson.