A simple pendulum was built from a small metal bob tied to a thin string clamped at a fixed pivot. Two experiments measured the period (the time for one complete back-and-forth swing) under different conditions.
A simple pendulum consists of a compact bob hanging from a light string of fixed length. When pulled aside and released, it swings back and forth. Students investigated what controls the period, defined as the time for one complete swing (over and back). To reduce timing error, they timed 10 swings with a stopwatch and divided by 10. In every trial the bob was released from the same small angle (about 10°) so that the size of the swing would not confound the results.
In Experiment 1, the bob mass was held constant at 100 g while the string length was set to 0.25, 0.50, 1.00, 1.50, and 2.00 m. The period was measured for each length (Table 1).
In Experiment 2, the string length was held constant at 1.00 m while the bob mass was changed to 50, 100, 200, and 400 g by using bobs of different metals of nearly the same size. The period was measured for each mass (Table 2).
Table 1: Period versus string length (bob mass held at 100 g; release angle about 10°)
| Trial | String length (m) | Period (s) |
|---|
| 1 | 0.25 | 1.00 |
| 2 | 0.50 | 1.42 |
| 3 | 1.00 | 2.01 |
| 4 | 1.50 | 2.46 |
| 5 | 2.00 | 2.84 |
Table 2: Period versus bob mass (string length held at 1.00 m; release angle about 10°)
| Trial | Bob mass (g) | Period (s) |
|---|
| 1 | 50 | 2.00 |
| 2 | 100 | 2.01 |
| 3 | 200 | 2.01 |
| 4 | 400 | 2.02 |
