Exhibit: Echo Tube
When you clap your hands, you suddenly compress the air between your hands. You hear this as a sudden loud noise.
When you clap near the end of the tube, part of the compression in the air goes down the tube. When it gets to the other end, the compression bounces off the closed end of the tube and comes back again. When this arrives at your ear, you hear the first echo.
The tube is about 15 metres long, so the trip down the tube and back takes about 1 tenth of a second because sound travels at about 300 metres per second through the air in the tube.
When this first echo gets back to the open end of the tube, part of the sound gets reflected back again to produce another echo. This process gets repeated every time the sound comes back to the open end – part of the wave gets reflected back. This is why you hear a sequence of echoes at intervals of a tenth of a second.