A simple, fun demonstration of resonance!
Listen as the plug slides inside the tube -- The pitch will rise as the resonant column of air gets shorter and fall as it gets longer.
"Groan Tubes are interesting for demonstrations of sound, but they can also be used to teach about free fall. Turn the tube so it starts to groan, and quickly toss it to a friend (so that the tube stays vertical). Listen. The groan stops when the tube is in the air and resumes when it is caught!"
Chris Chiaverina ~ Physics Teacher
Groan Tube measures at 15 1/2 inches in length with a 1 inch diameter.