Hands-on Science

Science World, Nov 22, 2004

PREDICT

Which type of material will serve as a better insulator (material that slows heat movement): vegetable shortening or trapped air? How much more heat will a layer of fat trap than no insulation layer at all?

YOU NEED

* 6 plastic bags (sealable, quart-size)

* small-bubble wrap (19 cm by 35 cm, or 7.5 in. by 14 in.) * thermometer

* duct tape (51 cm, or 20 in.) * vegetable shortening (375 ml, or 1.5 cups)

* three 1 L (2 pint) plastic bowls * two 2 L (1/2 gal) milk jugs--one filled with 43[degrees]C (110[degrees]F) tap water, and the other with 10[degrees]C (50[degrees]F) tap water * watch or timer * 30 ice cubes * 250 ml (1 cup) measuring cup * paper (graph and plain) * pencil

PROCEDURE

1. Form groups of 3 to 4 students.

2. Turn a sealable plastic bag inside out and insert it into another bag.

3. "Zip" the bags together, forming a "mitt." This mitt has no insulation--it's your control. Set the open mitt aside.

4. Get a new bag. Place 375 ml (1.5 cups) of shortening into it. Place a new inside-out bag into the shortening-filled bag.

5. Zip the bags together, forming a mitt. Then use your hand to evenly spread the shortening that's between the bags. The shortening is fat insulation. Set the open mitt aside.

6. Get a new bag. Fold a sheet of bubble wrap in half and place it into the bag. Place a new inside-out bag into the bag lined with bubble wrap.

7. Zip the bags together, forming a mitt. The bubble wrap is air insulation. Set the open mitt aside.

8. Pour 625 ml (2.5 cups) of 10[degrees]C (50[degrees]F) tap water and 10 ice cubes into each of three bowls. Measure and record the bowls' water temperatures.

9. Pour 250 ml (1 cup) of 43[degrees]C (110[degrees]F) water into each of the three mitts.

10. Measure the water temperatures inside the mitts. Record.

11. Seal the top of the mitts with 17 cm (7 in.) of duct tape.

12. Lower each mitt into a bowl so that the cold water just covers the water inside the mitts.

13. After two minutes, remove the mitts from the bowls. Untape them. Measure and record the mitts' inside water temperatures. Retape the mitts.

14. Repeat Steps 12 and 13 four more times, for a total of 10 minutes.

CONCLUSIONS

1. Make a three-line graph showing each mitt's water temperature over time. Did one insulator work best? Explain.

2. Would the mitts lose more heat in a cold room or cold water? (Hint: See Freeze Factor, p. 14.)

1. Answer may vary. Both fat and air are good insulators

2. Since water pulls heat from a material 2? times faster than air, the mitts would lose more heat in cold-water.