Kids can see for themselves how a greenhouse works, and relate this understanding to the greenhouse effect that occurs in Earth's atmosphere. It's a good opportunity to practice key science skills such as observing and recording data, using a control, and drawing conclusions from results. What's more, it's a great way to do some learning outside!
What You Do:
- Give your child the materials. Have him place both thermometers in direct sunlight.
- Wait about three minutes before reading the thermometers to give them time to adjust to the temperature.
- In his notebook, have your child create two columns, one for thermometer A and one for B. Alternatively, he can label them as Left and Right—whatever he prefers for identification.
- After three minutes ask your child to read both thermometers and record the temperatures in his notebook along with the time of the readings.
- Now, have him turn the jar upside down and place it over one of the thermometers so the jar is completely covering it. Conversely, you can put the thermometer into a see-through container and put the lid on it. Make sure the jar doesn't cast a shadow over the other thermometer. If the thermometer is too long to lie flat on the table with the jar over it, just prop it up inside the jar!
- Once every minute for 10 minutes have him record the readings of both thermometers, without touching them, in his observation chart.
- After the 10 minutes look over the chart with him. How did the temperature inside the jar change compared to the other one?
What's Going On?
The air over the exposed thermometer is constantly changing, constantly mixing with cooler air. While inside the jar the air is trapped and can't circulate, it simply gets warmer and warmer as the sunlight heats it up. This is similar to the way a greenhouse works, where solar energy (light) comes in and becomes thermal energy (heat) that can't escape back out through the glass house.
It's important to note that while this simple exercise mirrors how a greenhouse works, greenhouses don't really work the same way that the greenhouse effect does. The greenhouse effect is a complex interaction of light/heat and chemicals known as "greenhouse gases" in the atmosphere. Those chemical compounds and molecules are called "greenhouse" gases because on a basic level they cause the temperature of earth to be warmer than it would be without them, much like the glass panes of a greenhouse. And on a smaller scale the glass jar of this activity.
Did you know?
Greenhouse gases serve a natural and important function: they keep the surface of the Earth warmer—without them we'd experience temperatures more like zero degrees Fahrenheit, or -18 degrees Celsius! Industrialization has led to what we call pollution, which creates more greenhouse gases, such as carbon dioxide. It's the excessive amount of these gases present in the atmosphere that scientists argue increases the temperature of the Earth and affects the balance of natural cycles.
Greenhouse Effect in a Jar adapted with permission from http://sln.fi.edu/tfi/activity/earth/earth-5.html The Franklin Institute Resources for Science Learning.