Physics of Noise

By George Grow

This is Bill White with the VOA Special English SCIENCE REPORT.

Imagine yourself in a quiet theater. Perhaps you are enjoying a play or carefully listening to a musical performance. Suddenly, you hear a person sitting near you noisily removing paper from a food product. Such noise often can anger people. It may even ruin a performance.

American scientists now say they have discovered why candy wrappers make so much noise when opened in a quiet theater. The scientists found that removing wrapping paper from an object makes a sound no matter how the wrapping is opened.

The discovery was made by two scientists. They are Eric Kramer of Simon's Rock College of Bard in Great Barrington, Massachusetts and Alexander Lobkovsky of the National Institute of Standards and Technology in Gaithersburg, Maryland. Their findings were reported at a recent meeting of the Acoustical Society of America in Atlanta, Georgia.

The two men recorded and studied the sounds made when a crushed piece of thin plastic changes shape. The scientists say the crushed plastic made noises similar to those made when a wrapper is removed from candy or other food. They describe the sound as a series of very brief bursts, or clicks. Each click lasts about ten-thousandths of a second or less.

Before making the recordings, the scientists crushed the plastic by hand thirty to forty times. They found a piece of plastic that has not been crushed opens rapidly when crushed. However, already crushed plastic opens up more slowly. They say such plastic may have more trouble opening up when released.

Mr. Kramer said the thicker pieces of plastic made fewer noises when opened. These sounds were louder, however. The scientists say plastic wrapping stores energy. They say the stored energy helps the plastic to open up again, at least partly, without being pulled. They say the plastic continues to open and release energy until the stored energy is no longer strong enough to force the movement.

Mr. Kramer says candy wrappers will continue to make sounds every time they are opened. His suggestion for people wanting something to eat in a quiet theater: Open it as quickly as possible.

This VOA Special English SCIENCE REPORT was written by George Grow. This is Bill White.