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Second's pendulum
Beginner
A pendulum with a two-second period, about one metre long.
A pendulum with T = 2 s has L = gT²/4π² ≈ 0.994 m. Used for timekeeping and for finding g.
At the equator L is slightly shorter.
Don't assume 1 m exactly.
In more detail
A seconds pendulum has a period of two seconds, one second for each swing. Its length is about one metre at Earth's surface, which made it a standard for clocks.
Real-world uses
- Historical clocks were built around seconds pendulums.
- Measuring g using a pendulum of known length and period.
- Older clocks were built with a pendulum of about one metre length, which swings once each second and gives a two-second full cycle.
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Frequently asked questions
Why is it called a seconds pendulum?
Because each swing takes one second, so one full cycle takes two seconds.
How long is it?
About 0.994 metres at sea level, depending on the local value of g.
Why is the second's pendulum about one metre long?
Its period is two seconds, and the formula T = 2π√(L/g) gives a length close to one metre at Earth's gravity.
Related topics in Oscillations & SHM
Pendulum at large amplitude · Physical pendulum · Torsional pendulum · Simple pendulum in elevator · Energy in SHM · Kinetic and potential energy in SHM