ANALYSIS
Divide the total time by the number of complete swings to find the time T of one swing. This time is called the period of the pendulum. Using this equation for the period of a pendulum T=(2p)sqrt(L/g), calculate the value for g. If you measured L in cm, your value should be 980 cm/s^{2}. Calculate your percent error, it should be about 1%. Which of your measurements do you think was the least accurate?
If you believe it was your measurement of length and you think you might be off by as much as 0.5 cm, change your value of L by 0.5 cm and recalculate the value of g. Has g changed enough to account for your error? (If g went up and your value of g was already too high, then you should have altered your measured value of L in the opposite direction. Try again!)
If your possible error in measuring is not enough to explain your difference in g (your % error), try changing your total time by a few tenths of a second  a possible error in timing. Then you must recalculate T and g.
If neither of these attempts work (nor both taken together in the appropriate direction) then you almost certainly have made an error in arithmetic or in reading your measuring instruments. In this case you should repeat the experiment. Your value for g should not differ from the accepted value more than one unit in the third digit.
QUESTIONS
1.How does the length of the pendulum affect your value of T?
2. How does the length of the pendulum affect your value of g?
3. How long is a pendulum for which T = 2 seconds? This is a useful timekeeper.
4. Which experiment gave you the lowest percent error? Explain fully.
Download a pdf version.
