Physics Lab: Pendulum Motion 1

Goal: To measure gravitational acceleration near the earth's surface

Materials:

• A single object to act as a weight for the pendulum (use a standard weight.)
• 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 (cell phone stop watch function is ok).

Procedure

1. Practice with your timing device so that you know how it works and can time intervals accurately.
2. Determine and record the mass of your weight.
3. Tie the weight to the end of the string.
4. Tie the string to your hook.
5. Measure as accurately as possible the distance between the hook and the center of the masses; this is your pendulum length L.
6. Displace the pendulum (measure the horizontal distance x of the displacement of the pendulum from its rest position.)
7. Measure the length of time required for the pendulum to make 10 complete back-and-forth swings (10 periods). Determine the value of T.
8. Repeat at least twice.

Data Handling

1. Average your values for T.
2. Using the average value, determine the acceleration due to gravity for your test mass. As we see in chapter 11, the formula for the period of a pendulum can be reformatted to give a formula for gravitational acceleration if we know the period of our pendulum and its length: $$\begin{array}{l}T=2\pi \sqrt{\frac{L}{g}}\\ \frac{T^2}{4{\pi }^2}=\frac{L}{g}\\ g=\frac{4{\pi }^{2}L}{T^2}\end{array}$$
3. Compute and average value and deviation your results.
4. Compare your average with the accepted value (9.8 meters/second²) and explain any differences.

Report

1. Describe your materials, equipment, an procedures in sufficient detail that your fellow students could repeat your experiment.
2. Report your data. Be sure to indicate the amount of error in your measurements. For example, if you can only measure a mass of 25g within 1 gram, your error would be 25 ± 1, or 1/25 = 4%.
3. Present your data in an organized form, preferably in a table, in such a way it is easy to compare results as you repeat trials or vary a specific contributing factor.
4. Show a sample calculation, if you have calculated values.
5. You may use a spreadsheet to calculate your information and create your table.
6. Summarize your results: is this an accurate way to determine gravitational acceleration?
7. Suggest at least one way to improve your experiment.

Upload your report to the Moodle Lab Assignment for this Lab.

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