STEP 2 Timer: Pinch the string between your fingers at the knot. Hold the pendulum so it can swing gently back and forth without hitting anything. Don’t swing the pendulum—keep your hand still. Be sure you can see the second hand of the clock, so you can tell your partner when to start. Read the time after 10 full swings.

STEP 3 Counter: Hold the meter stick so one end lines up with the pendulum string. Pull the washer to the side 15 cm (no more).

STEP 4 Counter: When the Timer says “Go!” let go of the pendulum washer. Keep track of the number of back and forth pendulum swings and say “Stop!” just when the pendulum completes its 10th back and forth swing.

Record your measurement in your data table for trial 1.

STEP 5 Repeat Steps 2 through 4 for trial 2.

Record your measurement in your data table for trial 2.

STEP 6 Exchange roles and repeat Steps 2 through 4 for trials 3 and 4.

Record your measurement in your data table for trials 3 and 4.

STEP 7 Determine the best value and the uncertainty for your data. See How To Make and Interpret Experiment Measurements found in the Appendix.

Record your best value and the uncertainty in the table on your record sheet.

Then complete the following sentence on your record sheet:

Our team’s best value for the time for 10 swings is _____ s (seconds) with an uncertainty of _____ s.
This means that the true value is probably within the range between _____ s and _____ s.

STEP 8 Your teacher will have drawn or posted a thick horizontal line with markings for the number of seconds for 10 back and forth swings. Tape the knot of your pendulum string along the horizontal line, using your best value.

Complete the class graph on your record sheet.