Activity Time: 10 minutes to set up; an hour to record results
Recommended Grades: 1 - 8 (Adults may help younger scientists.)
Objectives: Explore what happens when an open and a covered container are exposed to light

• 2 identical clear containers, glass or plastic
• 2 thermometers; a kitchen cooking thermometers will work
• 2 moist paper towels
• a sunny spot or 2 identical lamps with identical bulbs
• clear plastic wrap or glass cover for one of the containers
• a timer
• a piece of paper and pencil to record the temperatures of each container

1. Place a damp paper towel in each container.
2. Place a thermometer in each container.
3. Cover the top of one container with plastic wrap or clear cover.
4. Place both the containers (one covered and one uncovered) in the sunlight or under a lamp that shines directly down on them. Make sure the containers are in the same amount of sunlight or the same distance from the lamp.
5. Record the starting temperature in each container. (These should be the same.)
6. Set your timer for 20 minutes, then check and record the temperatures again.
7. Repeat the 20-minute cycle two more times, recording the temperatures after each 20-minute period.

The energy in the sunlight or lamp heats up moist air in the containers. Hot air rises because as air heats up, the air molecules expand. This means there is more space between hot air molecules than cold air molecules. This makes the hot air molecules lighter than the more closely packed cold air molecules.

In the open container the hot moist air rises and mixes with the air in the room. In the covered container the hot air is trapped by the plastic wrap. In an enclosed greenhouse garden, the same process keeps the temperature and humidity high enough to grow non-seasonal plants.

You may have noticed water forming on the inside of the plastic wrap on the covered container. Hot moist air inside the covered container comes in contact with the plastic wrap that had cooler air from the room on the outside of it. The water vapor in the moist air changed from a gas into a liquid as it cooled.

The greenhouse effect is a way to think about why Earth’s temperature is rising. Gases including carbon dioxide, water vapor, nitrous oxide, and methane are entering our atmosphere and trapping energy that would otherwise radiate off into space.