Why does the time period of the pendulum increase when its length is increased?

For a simple pendulum, where the pendulum is itself
considered of negligible mass which moves with a minimal amplitude, the time period is
given by the formula

T =
2(pi)*(sqrt(L/g))

where T is the time period, L is the
length of the pendulum, and g is the gravitational constant.  By lengthening the
pendulum, the weight at the end must travel a longer distance as it swings, which means
more time is required for it to complete a given period.  See the link below for a
simple pendulum calculator, enter values for different lengths and verify this for
yourself: