How do air conditioners cool the air? One of our favorite websites, How Stuff Works, has an excellent description of how air conditioners and refrigerators work. Take a walk around the school to locate your school's air conditioner and compare it to units used in homes. Have students determine what type of air conditioner they use in their own home. Some homes will have central air, some may use window units, and some may even have industrial cooling systems if they live in an apartment.

The cooler you set the temperature on an air conditioner's thermostat, the longer it has to run to cool a room, and the more it costs. By turning the thermostat up just a few degrees, you can save a lot of energy! Why is it important to save energy? How much does energy cost?

Thermometer Field Trip
Take a thermometer on a field trip! Make a chart to record your observations of the situations below.

• Put a thermometer in front of an electric fan. Leave it for five minutes and then check the temperature. Turn off the fan and wait five minutes to make sure the thermometer has time to change, then check it again. Is there a difference? Why or why not?
• Take the temperature of the air, then take your thermometer for a swim by dipping it in water and checking the temperature. (Make sure it is a waterproof thermometer.) Remove the thermometer from the water and watch the temperature is it as it dries. You can lengthen the time the thermometer takes to dry by using a rubberband to hold a piece of a paper towel around the bulb of the thermometer. Get the paper towel wet along with the thermometer and watch the temperature as it dries in the hot sun. What happens? What happens if you use a fan to blow air across the wet thermometer bulb?
• On a sunny day, try taking temperatures in the open sun and in the shade. Is there a difference? Where is it warmer?
• Take the temperature in a basement. If you can't go to a basement, take the temperature of cold water from the water tap. Water pipes are buried deep underground, so the temerature of the water will be similar to that of a basement. How much cooler is it underground than on the surface?

Based on your observations, what can you do to keep cooler and save energy this summer? Closing the blinds at home and at school will have the same effect as being in the shade. Spending time in the basement at home will also help you to stay cool. You might also keep in mind that because hot air rises, opening a window on the top floor of your house will help to let out the hot air at night, when the temperature outside is lower.

Dog Days of Summer

Where did they come up with that expression, anyway? According to the American Kennel Club, one theory comes from the ancient Romans who maintained that when the Dog Star, Sirius, rose with the sun, the heat from the two stars raised the
temperature on Earth, hence the "Dog Days of Summer."