The Seconds Pendulum

An interesting historical fact from these MIT notes: Christiaan Huygens proposed defining the meter conveniently as the length of a pendulum that produces a period of 2 seconds. A pendulum’s period is

\displaystyle  T = 2\pi \sqrt{\frac{l}{g}},

so, using Huygens’ standard of T = 2s for 1 meter,

\displaystyle  g = \frac{4\pi ^{2}\times 1\ \textup{meter}}{4s^{2}} = \pi ^{2}ms^{-2}.

“So, if Huygens’s standard were used today, then g would be π2 by definition.”