Distribute the Student Project Description. Have students present their ideas or comment on their proposed designs. Test the working prototypes. Humans hear sounds with frequencies between 20 and 20,000Hz. Water waves are different from sound waves because they rely on gravity to exist and involve an interface of two different fluids.
Sound waves are actually waves of changing pressure.
After you place the material in the water, drop BB's at one end and observe the behavior of the waves as they are reflected from the material. Reflectors of sound and water waves are used in many applications and can be demonstrated with a large pail of water, some pieces of common materials and some BB's. To demonstrate how waves are reflected from different surfaces, use a rough and jagged piece of concrete, a soft and fluffy piece of fabric, and a smooth piece of wood or Formica. For best results, create a sand bank perimeter in bottom of the pail to act as a non-reflecting border. Use only a small amount of water in a setup like that shown in figure 4.