Why is it better to time a large number of oscillations to determine the period of a pendulum?

Answer 1

Timing a large number of oscillations accounts for instrument error. If each oscillation takes exactly 1.0001 seconds, but the timer can only measure to the tenth of a second, it takes 1000 oscillations to detect the fractional second. If this pendulum is being used for something for a very long period of time, the error might result in a significant drift in behavior. If this pendulum runs a grandfather clock, the clock will lose 1 second every 10000 seconds (approximately 3 hours). This accounts for 8 seconds per day, nearly a minute per week, and about 50 minutes per year. This might be acceptable for a novelty piece like a grandfather clock, but if it governs something more important, it will have a significant effect.

Accounting for minute differences like this is one of the more annoying parts of scientific method, called scientific rigor. It's important in real experiments, and indoctrination of science students in rigor starts long before the students start doing stuff where it's practical, so it often frustrates students a great deal.

Answer 2

Because you can get an average, to better account for errors in measurement