
Using the radius, we calculated the circumference of the circle which the pendulum traveled along. Since the ratio of the angle swept out to the number of degrees in a circle is equivalent to the ratio of the arc length traveled to the circumference of the circle, we were able to calculate the length of the arc the pendulum traveled, and therefore the distance traveled.
Knowing the distance traveled by the pendulum and the amount of time it took to travel that distance, we were able to divide the distance by the time and calculate the average velocity of the pendulum between the two positions at the times of the two flashes.