An Experiment With Sound Waves

Here is an experiment dealing with sound waves that is extremely illuminating. It is just the thing for a gathering of young friends who are scientifically inclined. Stretch a piece of string tightly across the room and on it pin a silk handkerchief or any other handy article made of silk-the larger the better.

When the handkerchief is hanging vertically, place your ear close to the middle of it, no more than an inch away. Then get a friend to “twang” an ordinary table fork on the other side of the handkerchief. You will hear the musical sound quite as plainly as though the silk fabric was not between your ear and the fork. Now dip the handkerchief in water and hang it up again. Place your ear as before and ask your friend to repeat the “twanging”. This time the musical sound will be almost inaudible. It would be practically unheard if the fabric were as large as a sheet. The sound you hear comes round the sides.

What is the explanation? In the first case, there is air all the way from the sound to your ear and the waves are uninterrupted; but in the second case there is air, water, and air. The sound is reflected back when it reaches the water and is lost as far as your ear is concerned.