From its discovery around 1602by Galileo Galilei, the regularmotion of pendulums was used fortimekeeping, and was the worldsmost accurate timekeepingtechnology until the 1930s.The word pendulum is newLatin, from the Latin pendulus,means hanging‘
The simple gravitypendulum is a weight(bob) on the end of amassless cordsuspended from africtionless pivot.When given an initialpush, it will swingback and forth at aconstant amplitude.
The period of swing of a simplependulum depends on its length, andthe local strength of gravity.If the amplitude is limited to smallswings, the period (T) or the timetaken for a complete cycle of asimple pendulum, is:
For small swings, theperiod of swing isapproximately the samefor different sizeswings. So, the periodis independent ofamplitude.This property, calledisochronism, is thereason pendulums are souseful for timekeeping.Successive swings of the pendulum, even if changing in amplitude, take the same amount of time.
External factors:TemperatureThe largest source of error in earlypendulums was slight changes inlength due to thermal expansion andcontraction of the pendulum rod withchanges in ambient temperature.
External factors:Atmospheric pressureViscous air resistance slows thependulums velocity. This has anegligible effect on the period,but dissipates energy, reducingthe amplitude
External factors:GravityPendulums are affected bychanges in gravitationalacceleration, which varies by asmuch as 0.5% at differentlocations on Earth, so pendulumclocks have to be recalibratedafter a move