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. A real pendulum’s period depends weakly on amplitude when swings are larger, and damping gradually removes mechanical energy. This lesson restricts amplitude to modest angles and holds gravitational acceleration fixed. Compare complete cycles rather than a single crossing, and do not confuse the mass of the bob with its distance from the pivot.
Forces, motion and energy · Discover & try
What changes a pendulum’s swing time?
Reading level 5 of 5 · AdvancedChange
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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