What You Do:
- Add equal parts tap water and rubbing alcohol to the bottle, filling it about a quarter of the way up.
- Add a couple drops of red food coloring and mix by shaking the bottle.
- Put the straw in the bottle, making sure it doesn't touch the bottom.
- Use the modeling clay to seal the straw in place. Leave a portion of the straw sticking out from the bottle, making sure the clay forms a tight seal around the straw and over the bottle mouth, but don't close off the straw's opening.
- To test if the homemade thermometer works, have your child place his hands around the bottle and observe what happens to the mixture.
Other ways to test the thermometer include placing it in a windowsill and observing how it reacts to the heat or cold there, or placing the thermometer in a bowl of hot water (always be careful!), followed up by placing the bottle into the refrigerator and the freezer.
What's Going On?
Just like any thermometer, the mixture expands when it's heated. As the alcohol-water mixture expands it moves up through the straw. If the bottle were to get very hot, the liquid would come through the top of the straw.
As an extension, mark a scale for the thermometer; you'll need a real thermometer. Have your child place his homemade thermometer in one area and use the store-bought thermometer to identify the exact temperature. Mark the line of the liquid on the bottle and write its value. Then, encourage your kid to find other areas of varying warmth or coolness to create a temperature range for the thermometer.
Mike is a 20-year veteran science teacher, and runs an online business (www.scienceinabag.com). Over the years Mike has studied trends in science, education, and finance, conducting research, developing programs, and writing articles on these topics.