A pendulum swings back and forth from a support. One complete swing returns to the same side moving in the same direction. A longer string makes a slower cycle. A heavier bob does not change the cycle time in this small-swing model. In this small-swing model, four times the length gives twice the cycle time.
Forces, motion and energy · Discover & try
What changes a pendulum’s swing time?
Reading level 1 of 5 · EarlyChange
Word help
Period
The time for one complete repeating cycle.
Amplitude
The largest displacement from equilibrium in an oscillation.
Pivot
The fixed support about which the pendulum swings.
Watch · Try · Explain
See how it works
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Ideal small-angle pendulum with a massless fixed-length string; no damping or large-angle correction.
What to look for
- Use the cycle count: one complete cycle takes about 1.42 s.
- The cycle time stays the same in this ideal model.
- Four times the length gives twice the cycle time.
Explain what you noticed
A separate ideal small-angle pendulum has its length increased from 0.5 m to 2 m at the same gravity. How does its period change?
Keep this idea: For small swings in the ideal model, length and gravity set period; bob mass does not.
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