Roasting marshmallows over a campfire to make s'mores is a favorite staple on many camping trips. However, more ways exist to generate heat than fire or traditional ovens. Try assembling the graham crackers, chocolate and marshmallows in a shallow glass baking dish and sealing it securely with clear plastic wrap. Set it outside in a sunny location, preferably at 85 degrees F or more. The chocolate and marshmallows absorb the heat energy of the sun, making them melt into soft gooey, edible goodness. Explain that the sun's energy liquefies solid-matter molecules, causing some types of matter to melt.
Some children learn best when the subject is put to music that stimulates their rhythmic impulses and allows them to move. You can make up your own song explaining the properties of matter or changing states of matter. Alternatively, use recorded or online versions such as Garden of Praise's "Properties of Matter" song.
Turn your lesson into a dramatic game that illustrates the process of changing states of matter. Gather the children in a large area and instruct them to move around freely and randomly like fast-moving gas matter molecules. After 30 to 60 seconds, tell them that a cold wind moved into the area, removing energy, slowing down the molecules and drawing them closer together. They should gather in a smaller area in the center of the room or field where they still have room to move around but not as quickly or freely, like liquid molecules that take the shape of the container in which they are placed. After another minute or so, tell them that the temperature dropped below freezing, taking even more energy, solidifying all liquids into solids. This stops all molecule movement and condenses the molecules into a tight formation. Everyone should freeze and grab onto the arm of another student with each hand, standing as close together as possible. Continue with the reverse process. When you finish the game, discuss how each part relates to what happens to matter molecules as energy is added or removed.
Experiment with different heating and cooling sources for butter, chocolate, ice cubes, wax and cheese, such as hot or cold water, solar energy, shade, a light bulb, wind, stove top, microwave, refrigerator and freezer. Measure the length of time it takes for each substance to liquefy or solidify using each heating or cooling method. Discuss how temperature affects the energy produced by molecule movement within the different types of matter.