Passage
Students measured the pull force of small magnets on a steel washer, using a spring scale that read the force in force units (fu). In each trial they recorded the greatest pull the magnet exerted on the washer as the washer was slowly drawn away.
Study 1: Using a single magnet, the students varied the distance between the magnet and the washer and measured the pull force at each distance (Table 1).
| Distance (cm) | Pull force (fu) |
|---|
| 1 | 80 |
| 2 | 40 |
| 3 | 22 |
| 4 | 14 |
| 5 | 9 |
Study 2: Holding the distance at 2 cm, the students stacked identical magnets together and measured the pull force for different numbers of stacked magnets (Table 2).
| Number of magnets | Pull force (fu) |
|---|
| 1 | 40 |
| 2 | 75 |
| 3 | 105 |
| 4 | 130 |
The same washer and the same spring scale were used in every trial.
