The period of a
pendulum is the amount of time it takes for it to move along its entire
distance. (From one end to the other and back, for instance.) This is described by:
T = 2pi(l/g)1/2
Where T is Time, l is legth of pendulum in meters and g is gravity in m/sec2 (9.8 on earth, give or take for altitude/air pressure/your professors anal-retentiveness.) The reciprocal of T is the frequency (how often the pendulum completes per second.)
However,
the fun continues! A similar formula can be used to describe the frequency and period of an
oscillating body, say a spring:
T = 2
pi(
m/
k)
1/2
yadda yadda ya, m is mass and k is our given spring coefficient.
2pi is taken from the formula for the circumference of a circle, the square-root of length over gravity creates a description for the circumference of our hypothetical circle.