Question 40
Use water waves as an analogy for sound waves. You need a shallow tray, a white sheet at its base, and a piece of wood with two identical nails inserted part-way. The distance between nails must be less than half the tray width. Put water in the tray to a depth of about 2–3 cm. Hold the wood so that the nail heads just touch the water surface. Move the wood up and down so the nail heads make waves. Observe the pattern where the waves meet.
