Figure 2. Cross-section of a vaporizing pot burner.

Energy is "capacity (or ability) to do work," and work is "the result of a force acting through some distance." A car running into the rear of a stalled car exerts a force on it, pushing it some distance, doing work in the process. The capacity of the moving car to do work is termed its kinetic energy. The greater a car's speed and/or mass, the greater its capacity to do work—that is, the greater its kinetic energy.

Formally, the kinetic energy (K) of a mass (m) moving with speed (v) is defined as K=1/2 mv ². Kinetic energy is measured in joules (J) when m and v are expressed in kilograms (kg) and meters per second (m/s). A 1,000-kg car traveling 15 m/s (about 30 miles per hour) has 112,500 J of kinetic energy. Kinetic energy depends much...