Passage III

When an object falls from a low altitude to Earth and gravity is the only force acting upon it, the object will have an acceleration of 9.8 meters/second² (m/sec²).

Using a stopwatch that is accurate to the nearest 0.01 sec, students measured the times for 2 spheres to fall to Earth and used these times to calculate the spheres' acceleration.

Experiment 1

The students measured the times required for a 200 g wooden sphere and a 50 g plastic sphere to fall 2.5 m to Earth. The spheres had equal radii. (Note: A sphere's surface area is proportional to its radius squared; its volume is proportional to its radius cubed.) The results are shown in Table 1.

For the wooden and plastic spheres, the average times were 0.79 sec and 0.80 sec, respectively, and the average accelerations were 8.0 m/sec² and 7.8 m/sec², respectively.

Experiment 2

The procedure in Experiment 1 was repeated for the same spheres falling 9.7 m to Earth. The results are given in Table 2.

For the wooden and plastic spheres, the average measured times were 1.46 sec and 1.60 sec, respectively, and the average accelerations were 9.1 m/sec² and 7.6 m/sec², respectively.

Experiment 3

The students tested the hypothesis that the stopwatch was not being started or stopped at the right moments. Using the stopwatch and a blinking light that flashed every 1.00 sec, the students measured the time interval between adjacent flashes. The results are given in Table 3.

The average time recorded in Table 3 was 1.06 sec.