Passage V

Potential energy (PE) is stored energy. Kinetic energy (KE) is energy of motion. An object's total mechanical energy is the sum of PE and KE. Objects in motion lose total mechanical energy because of friction.

Students conducted 3 experiments to study mechanical energy.

Experiment 1

In a vacuum chamber, a sphere on a string was released from various heights (h) and allowed to swing. For spheres of different masses, PE and KE (in joules, J) were determined at h and at the lowest point of the swing, as shown in Figure 1. The results are given in Table 1.

Experiment 2

Carts having different masses were placed on a track in the presence of air. Starting from rest at Point A, each cart was allowed to roll, as shown in Figure 2. The results are given in Table 2. (Note: At Points B and D, a cart's PE = 0.)

Experiment 3

A toy consisted of a spring affixed to the inside of a box. The spring had much less mass than the box. When the toy was dropped and hit the floor, the spring compressed and then extended, throwing the toy upward, as shown in Figure 3.

The students tested 3 toys having the same mass but springs with different stiffnesses. The students dropped each toy through the air from 1.0 m above the floor and observed the maximum height reached by the toy on its first bounce. The results are given in Table 3.