The period of a pendulum is given by the formula T = 2 * pi * sqrt(l / g) where l is the length of the string, and g is about 9.81 m/s.2.
http://wiki.answers.com/Q/How_does_the_length_of_t...

Pendulum period in seconds. T ≈ 2π√(L/G) L is length of pendulum in meters. G is gravitational acceleration = 9.8 m/s². Length for 1 second = 0.248 m.
http://answers.yahoo.com/question/index?qid=200902...

The equation for a pendulum's period is T = 2 * pi *
http://www.chacha.com/question/whydoesthelength...

There are two things right out of the gate without getting very technical: 1  The weight of the added pendulum arm length affects the force needed to swing the pend back and forth,
http://www.tutorvista.com/answers/whydoeschangin...
