Physics describes energy as constantly changing states and moving between objects, a fact that students can model by releasing two balls over one another. Students hold up a large basketball and a smaller tennis ball, releasing the two so that the tennis ball lands over the basketball. Once the larger ball has made contact with the ground, it strikes the tennis ball above it, causing it to bounce even higher. Students will see how the potential energy stored in the two bouncing balls is transformed into kinetic energy, as well as how energy is transferred to the tennis ball as it is pushed up by the basketball. Remind students that energy is neither created nor destroyed, simply transferred.
In chemistry, students learn that compounds store energy, which is released through reactions and combustion. In a classic exothermic reaction, a reaction that releases energy into the environment, students make a small pile of potassium manganate crystals. Wearing safety glasses and observing the appropriate laboratory safety regulations, they add a large drop of glycerol into the center of the pile. After a few seconds, the reacting compounds begin to give off steam, eventually creating a small flame and leaving behind a small pile of black ash. Students should take note of how energy stored in the compounds is released into the environment in the form of light and heat and how the elements take on a new physical configuration with a lower energy state.
With nothing more than a shoe box and tin foil, have students design a small solar cooker by covering the interior surface of the box in tin foil and suspending a hot dog in the box with cardboard supports. Place the box in direct sunlight. Optionally, students can cut a curved bottom surface into the box and cover the curve with tin foil to increase the efficiency of the oven. In any case, students will observe how solar heat is reflected onto the hot dog, provoking physical changes (cooking). This lesson is useful for understanding thermal (heat) transfers, uses of renewable energy and the importance of the Sun as the energy source for biological and physical processes on Earth.
For students with a basic understanding of how thermal and energy transfers work, a simple experiment with insulation materials illustrates how applied science tries to take advantage of these dynamics in real-life situations. Have students line pieces of plywood in different materials, such as fiberglass, rock wool, cellulose and polyurethane foam. Place the lined pieces of plywood over a second piece of untreated plywood and point a hot hair dryer at the center of the lined piece for about 15 minutes. After turning off the hair dryer, students record the temperature of each lined piece of plywood and the piece of plywood behind it. Gather evidence that, where the temperature difference is greatest, the use of certain materials helps keep heat on the surface without transferring it to neighboring objects. The experiment helps students understand how different materials undergo heat transfer processes differently and how this fact is used in practical applications like home insulation.