Straw, Wood or Brick: Which Insulates Best?

Research Questions:

• What heat transfer?
• Assuming the air is still (and there’s no cold air source such as an air conditioner), does a room cool because the hot air left the room or because cold air came in the room?
• What types of materials make good insulators?

Heat transfer occurs when heat moves from one area to another such as from a fireplace to a cold room. According to the second law of thermodynamics, heat always moves out to a cooler area, not cold air into a hot area. Insulation is any material that slows down heat transfer. Homes in cold areas are always insulated. This insulation prevents the heat transfer from the inside of the house to the cold outdoors. The effectiveness of insulation is measured by a U value. U values describe how effectively a material conducts heat. Good insulation has a low U value, meaning that heat transfer is minimal. Issues related to choosing insulation for a home include the flammability of the insulation, cost and chemicals in the insulation.

Materials:

Most supplies are probably already available at home. Sand can be obtained from a sandbox and woodchips can be obtained from the yard or from a garden supply store. See if you can borrow a good thermometer from school.

• Box #1 should be a small closed box big enough to hold an upright 250 ml Erlenmeyer flask of water. Metal or plastic card boxes designed to hold 5” x 8” cards or small plastic freezer containers are useful
• Box #2 should be big enough for the first box to nest in. You might have something already around the house. Search the area of a discount shop dedicated to closet supplies and storage ideas for a heavy plastic box. An old-fashioned metal milk box for the delivery of milk also works. You need something big enough that leaves at least 4” around all sides of the small closed box, including the top and the bottom.
• Straw (enough to densely pack the second box)
• Wood chips (enough to densely pack the second box)
• Sand (enough to densely pack the second box)
• A good thermometer
• A 250 ml Erlenmeyer flask with a stopper
• Styrofoam packing peanuts (optional)

Experimental Procedure:

1. Fill the Erlenmeyer flask with 250 ml of boiling water. Measure the temperature of the water. Put a stopper into the Erlenmeyer flask.
2. Put the Erlenmeyer flask into Box #1, taking care not to tip the flask when you handle the box. Close Box #1.
3. Pack the bottom of Box #2 with sand. After you have laid down 2-3 inches of sand, put box number 1 into Box #2. Continue packing box #2 with sand. When you are down, close Box #2.
4. Every half hour, open your boxes, uncork the flask and take the temperature of the water. Record the temperature and then repack the boxes just as you did in steps 2 and 3. Continue checking the temperature for at least 4 hours.
5. Graph your results. Your y-axis will be temperature and your x axis will be time.
6. When you are done, clean out your boxes and repeat with wood chips and straw. If you have time, consider repeating with Styrofoam packing peanuts. Graph your data.
7. Did you ever reach thermal equilibrium? Which was the best insulator? How can this information be used?

Terms/Concepts: Heat transfer; Insulation; Second Law of Thermodynamics; U value; Thermal equilibrium

References:

Websites

Lowes: Understanding Heat Transfer and Insulation

http://www.lowes.com/cd_Understand+Heat+Transfer_974680410_

School for Champions: Thermal Insulation Prevents Heat From Escaping

http://www.school-for-champions.com/science/thermal_insulation.htm

About.com: Introduction to Heat Transfers

http://physics.about.com/od/thermodynamics/f/heattransfer.htm