To demonstrate how different substances reflect sound waves. Put the ticking watch or clock in the end of one tube, then put your ear up to the end of the other tube. Have your partner take the plate away. Now have your partner hold the piece of foam or carpet up instead of the plate.
Sounds can come from all different directions.
Much like a mirror that reflects light, hard surfaces reflect sound. When the plate is held up at the ends of the tubes, the sound vibrations from the watch travel down the tube, bounce off the plate, and travel up the other tube to your ear. Bouncing sound is the method used for charting ocean depth, as well as the way that whales sense information about other objects in the ocean. To measure ocean depth, ships use oscillators to produce sound waves travel through the water. An instrument called a fathometer records the time it takes for sound waves to echo back off the ocean floor, and with that information estimates ocean depth.