Goal: To measure gravitational acceleration near the earth's surface
- Several masses (you could use coins, which makes it easy to double or triple masses).
- Strong string or nylon fishing line, able to support your weight without breaking.
- Hook on which to tie pendulum; should be fastened to make the pendulum as long as possible (I used the ceiling hook for a hanging plant).
- Stopwatch or watch with second hand.
- Weigh your masses.
- Tie them to the end of the string.
- Tie the string to your hook.
- Measure as accurately as possible the distance between the hook and the center of the masses; this is your pendulum length L.
- Displace the pendulum (measure the horizontal distance x of the displacement of the pendulum from its rest position.)
- Measure the length of time required for the pendulum to make 10 complete back-and-forth swings (10 periods). Determine the value of T.
- Repeat at least twice.
- Repeat your experiment, varying the mass by at least 25%.
- Repeat your experiment, varying the length of the string by at least 25%.
- Does the period change when you changed the mass? How will this affect your calculation for the gravitational acceleration?
- Does the period change when you changed the length? How will this affect your calculation for gravitational acceleration?
- Average your values for T.
- Using the average value, determine the acceleration due to gravity for all masses and lengths you used. [As we see in chapter 11, the formula for the period of a pendulum is T = 2π √(L/g).]
- Average your results.
- Compare your average with the accepted value (9.8 meters/second2) and explain any differences.
- Describe your materials, equipment, an dprocedures in sufficient detail that your fellow students could repeat your experiment.
- Report your data. Be sure to indicate the amount of error in your measurements. For example, if you can only measure a mass of 25 gms within 1 gm, your error would be 25 ± 1, or 1/25 = 4%.
- Present your data in an organized form, preferably in a table, in such a way it is easy to compare results as you repeate trials or vary a specific contributing factor.
- Show a sample calculation, if you have calculated values.
- If you did a series of experiments, varying something by increasing or decreasing a factor, try to plot your data (y-axis) as a function of the factor (x-axis).
- You may use a spreadsheet to calculate your information and create your table.
- Summarize your results.
- Draw conclusions about what is happening.
- Suggest at least one way to improve your experiment.
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