Simple gravity pendulum

[warriorofrovac]

why does the length of string attached to a pendulum affect the time it takes for one oscillation

[HallsofIvy]

This is a homework problem? Then show us what you have done on it and what you DO know about the situation. One reason for that (in addition to the fact that the more you do the better) is that it helps us know what kind of help you need and what would make sense to you. I know several ways of answering this question. One involves using a simple formula for the period of a pendulum that you may or may not know. Another involves solving a linear differential equation, that approximates the motion of pendulum, to derive that formula. Still a third involves using properties of a very difficult (and not solvable exactly) non-linear differential equation that exactly models the pendulum. I have no way of knowing if any of those are appropriate here.

[warriorofrovac]

a bob attachted to a piece of string
The length of the strings range from 30 to 100cm in 10cm intervals
the bob is pulled back roughly 6cm and let go
I time how long it takes for the bob to complete 10 oscillations and plot the results for all the lengths of the string, i get a graph which curves.

what i want to know is..why is the time less for one oscilation when the length of the string is shorter, against the time for when the length of the string is longer?