## Heat

Why it occurs: Summer brings warmer weather because of the tilt of Earth’s axis. During summer in the United States, the Northern Hemisphere is tilted more toward the sun, while the Southern Hemisphere is tilted away from the sun, creating winter in regions like South America and Australia.

How to show it: Give a water-filled spray bottle to each pair of students, and have them face each other, one holding the spray bottle (“the sun”) and the other holding his or her arm up (“Earth”), palm forward. Have the sun students spray as the Earth students hold their arms at different orientations. If their palms are tilted toward their partners, do their hands or their elbows get wetter? Discuss how the spray is like the sun’s energy; it doesn’t reach all parts of Earth with the same strength.

Extra credit: Explain that in addition to tilting on its axis, Earth also rotates around the sun. See if they can start with palms (North Pole) tilted closer to their partners, and make a half-circle around them so their elbows (South Pole) are closer. Hint: They’ll end up with their backs to their partners!

## Thunderstorms

Why they occur: When warm air near the ground rises, the water droplets in the air condense and become clouds, creating energy. If warm air continues to rise, a thunderhead can form and its energy can produce thunder and lightning.

How to show it: Make colored ice cubes by adding blue food coloring to water in an ice tray and freezing. Place a pan of warm water on the ground and let it sit for one to two minutes. Squeeze a few drops of red food coloring on one side of the pan and place a couple of the ice cubes on the other side. The red (warm) water will rise to the top of the pan as warm air does during a thunderstorm. The blue (cool) water will sink, as colder air does during a storm.

Extra credit: Have students blow into paper lunch bags, cinching them with one hand like a balloon. Then have them punch the inflated bags with their other hand. The resulting pop is similar to the pressure wave created when lightning strikes and causes thunder.

## Rainbows

Why they occur: Moisture in the air refracts sunlight, causing the white light to bend and separate into its constituent colors.

How to show it: Have small groups hold a glass of water over white paper in direct sunlight. The glass and water will refract the light, creating a rainbow on the paper. Kids can experiment by holding the glass at different angles and in different levels of brightness to see how that affects the rainbows.

Extra credit: Make more rainbows by squeezing a drop each of red, yellow, and blue coloring around the edges of a dish of milk. Add a drop of dish soap into the center. The soap will separate the fats in the milk, causing the colors to swirl and create a rainbow.

## Hail

Why it occurs: When warm air rises at a rapid rate during a thunderstorm, it can lift water droplets to a higher elevation, where they freeze and then begin to descend. The droplets may rise, freeze, and fall multiple times, creating hail of different sizes. Eventually their weight causes them to fall to the ground.

How to show it: Measure and weigh a small rubber ball (the “water droplet”). Have each child put a thick layer of white paint onto the ball. Measure and weigh the ball after five students have painted it, then 10 students, and finally the entire class. Talk about how the ball grew in size and weight as each student added a layer of paint, and connect this process to the growth of hail during a storm.

Extra credit: Have students bring in objects that are often referenced to describe the size of hail (e.g., peas, pennies, golf balls) to measure and compare.