Created by Dale Olive and Randy Scoville
Future Flight Hawai`i instructors
Demonstration at a glance:
Two students hold a test tube between them. A piece of glass tubing containing a bubble of colored water protrudes out of a one-hole stopper stuck into the test tube. When both students hold the test tube in their hands, the level of the liquid rises.
Choose a large test tube and find a one-hole stopper that fits it. Carefully insert a 10-12 inch piece of narrow glass tubing into the one hole stopper so that an inch or two protrudes below the bottom. Make a batch of dark food coloring. Insert the end of the tubing, below the stopper, into the liquid and stop the liquid by holding your thumb over the hole in the tubing. Quickly insert the stopper and tubing into the test tube and release your thumb. The liquid should rise or at least stay inside the tubing. Anyone holding the test tube will now make the liquid rise inside the tubing.
Whenever you heat up air in the test tube, with your hands or otherwise, the speed of the molecules inside increases. Because the tube is stoppered, the molecules have nowhere to go except up the tubing. As they pound against the bottom of the liquid in the tubing they push it up higher and higher.
What you're really making here is a homemade thermometer that operates on the expansion of air due to heat. Measurements could be taken to study Charles law, which states that temperature and volume are directly proportional. As the temperature goes up, so does the volume of a gas. To demonstrate that gases contract when cooled, I stick the thermometer in cold water to show the liquid retreating down the glass tubing.
Communications: Hawaii Space Grant Office
This activity is featured in Future Flight Hawaii, a K-12 Education Project of Hawaii Space Grant Consortium.
FEB 27 2001.