To determine the acceleration of a free fall by means of a simple pendulum?

Answer 1

It's perhaps even simpler:
The only thing holding you up for some seconds, while falling, is the speed of gravity. If you know the distance from top to bottom, the formula would be:
d=1/2g*t^2 (one half the gravity times the time to the square)
If you know the pendulum takes x amount of seconds to go from left to right and then back to the left, just count the times the pendulum went back and forth. Then insert that time on your formula.