The document discusses the layers of the Earth's atmosphere and their properties. It also describes how hot air balloons are able to fly by harnessing the principle that warmer air rises above cooler air. Additionally, it explains the greenhouse effect and how the atmosphere traps heat from the sun, maintaining temperatures suitable for life.

1. The Earth’s Atmosphere

5. Hot Air Balloons http://www. howstuffworks .com/hot-air-balloon. htm Hot air balloons are are based on the basic principle that warmer air rises in cooler air. Hot air is lighter than cool air, because when air heats, the molecules spread apart. While a cubic foot of air normally weighs about 28 grams, if the air is heated by 100  F, it weighs about 7 grams less. The reason hot air balloons are so huge is because about 65,000 cubic feet of hot air is needed to lift 1,000 pounds,

6. Image and more information on hot-air balloons can be found at: http://www. howstuffworks .com/hot-air-balloon. htm

7. The Greenhouse Effect (it’s natural- somewhat) The reason our planet is able to sustain life is because we have and atmosphere and something called the greenhouse effect. If you remember, when we studied the planets, those with no atmosphere were either really hot or really cold. Image courtesy of: http://www.green-planet-solar-energy.com/mercury-the-planet.html Mercury’s temperature varies from 200  F to 800  F even though it’s closest to the sun.

9. Click on the picture to see an animation of the greenhouse effect.

12. Land and Sea Breezes Uneven heating of air over land and water causes breezes near the shore. When the land is warmer than the water during the day, air above it rises, and a cool breeze blows in from the sea. As the land cools off at night, air pressure over it increases, and a cool land breeze blows out to the sea.