Secret Bells

1. Cut two lengths of string, each about two feet (0.6 m) long.
2. Tie one end of each string to a different side of the metal hanger, as pictured above.
3. Wind the free end of one string around your index finger a few times. Wind the other string around the index finger on your other hand.
4. Allow your assembly to swing freely from your two fingers.

Place your index fingers (with hanger assembly attached) gently on the small flap of skin just in front of your ears, closing off the ear canal without putting your fingers into your ears. Swing the hanger so that it bangs lightly against something hard, like the edge of a desk or a door frame, and then let the hanger hang free. As the hanger vibrates, you should hear the resulting sound ring through the strings like chimes.

To go further, try using different materials and see how well they work. Instead of using a metal hanger, for instance, try a cooling/baking rack or a pair of metal salad tongs.

Although most of the sounds we hear are transmitted through the air, air is not the only carrier of sound waves—nor is it the best. A ticking clock can be heard through the air if you’re close enough, but put your ear to the table with the clock on it and the ticking will sound much louder.

When something vibrates, the strength of the vibration and the length of time the vibrations continue can vary quite a bit, depending on the materials involved. Hit a piece of wood with a stick and the sound lasts for just an instant. Hit a metal gong with the same stick, and the sound may continue for many seconds. Water is another good transmitter of sound.

Why the difference? In some materials, the molecules are tightly packed together; in other materials, the molecules are more loosely arranged. How close the molecules are to one another can affect how easily they can bump into each other to start a vibration moving along.

When you hit the coat hanger against another object, it starts vibrating. The vibrations in the metal travel through the string and into your fingers. The vibration is transferred to your head through solid objects, not air. Compare the sound of the coat hanger swinging into a chair or desk without holding the string against your ears. The sound is much duller. This demonstrates how the same vibration sounds differently when it travels through different materials.

Sound is an organized motion. Heat is a random motion. Some materials, including lead, rapidly turn sound into heat. Others, such as quartz crystal, very slowly turn sound into heat.

This Science Snack is part of a collection that highlights Black artists, scientists, inventors, and thinkers whose work aids or expands our understanding of the phenomena explored in the Snack.

Source: Sonavi Labs

Dr. James West (1931–present), pictured above, is an inventor and acoustician. In 1962, Dr. West studied acoustics, and co-invented the foil electret microphone. Ninety percent of all microphones produced use this technology, which has improved performance, acoustical integrity, and affordability. He has over 250 patents, and many awards, including the National Medal of Technology and Innovation, and membership in the Inventors Hall of Fame. In this Science Snack, you explore acoustics by observing how sound travels in different materials.