How to Create your thermometer

Materials

• 2 cups of lukewarm water
• 2 cups of hot water
• bowl
• food coloring
• ruler
• clear glass soda bottle
• clear plastic straw
• Play-Doh
• marker
• thermometer
• a large pan

Procedure

1. Put two cups of lukewarm water into the bowl and stir in six or seven drops of food coloring. Fill the soda bottle with the colored water. Mold Play-Doh around the straw, about two inches (5 cm) from one end. Insert the straw into the bottle. Mold the Play-Doh around the top of the bottle to seal the straw. Do not let the straw touch the bottom of the bottle.

2. Let the bottle sit for a while at room temperature. Then use the marker to mark the water level on the straw. Take the temperature of the room with a real thermometer and write that number next to the mark.

3. Now set the bottle into a pan filled with two cups of hot water. Once the water level in the bottle has stopped rising, mark the new level on the straw. Take the temperature of the water in the pan and label that number next to the mark.

4. You now have a high temperature and a low temperature. Mark equally-spaced tics between the two numbers onto the straw. For example, let's say your low and high temperatures are 65°F and 80°F and the distance between the two marks is 1.5 inches. Measure at 0.5 inch increments between the low and high marks, adding 5° to each mark. So you'd have something like this:
Degrees:     65°     70°     75°     80°
Measure:     0"     0.5"     1"     1.5"

5. Now you have a calibrated thermometer!