In physics, energy is a measure of the amount of change that happens; for instance, things (objects) may start moving, making sound, or feeling warmer. We use the word energy to measure the amount of change that happens during these events. For example, if we tap a ball lightly, it will roll a short distance, resulting in a small change in energy, but if we push on a ball really hard, it will roll a big distance, resulting in a big change in energy. There are only two types of energy measured by scientists: the energy changes of moving things (kinetic energy) and the energy changes of things that have the ability to change (potential energy). Potential energy describes something that is capable of making a change but hasn't yet. When potential energy changes to movement, it becomes kinetic energy. We can measure kinetic energy by figuring out how many atoms it has and how far and how fast it goes. A pronunciation guide for scientific terms is included. 24 pages with full-color photographs and illustrations. Reading Level 1-3, Interest Level 2-5.