How Does a Whistle Work?

A referee's whistle.
••• Kuzmik_A/iStock/Getty Images

Whistles often pierce the fabric of daily life: a referee makes a crucial call in the final moments of a game; a crossing guard signals children that it's okay to cross the street; and a pet owner calls in a dog that has wandered too far. Trains or ships signal their approach. While the concept of the whistle is simple, learning how it works involves knowledge of both music and physics.

The Basic Idea

Woodwinds, like this recorder, are aerophones.
••• ahavelaar/iStock/Getty Images

A simple experiment illustrates the basics -- purse your lips and blow, or blow across a bottle opening. Whistles are aerophones, a family of instruments that produce sound by forcing an air mass through a restricted space, thus creating vibration. Aerophones include brass, woodwinds, pipe organs and even harmonicas. The typical whistle is constructed of metal, plastic or wood, with metal creating the strongest amplifying effect and wood creating the softest, as it absorbs more sound.

Inside the Whistle

Vibrating air creates sound waves in the resonate chamber.
••• AlexandrMoroz/iStock/Getty Images

Blowing a whistle forces air through the mouthpiece's rectangular tube until it runs into a slotted edge. The slot divides the air in two, creating oscillating sound waves that then tumble around the resonate chamber, or barrel. As the compressed air escapes from the hole on the other end, it creates an audible pitch. The pitch frequency is determined by length -- longer whistles produce lower pitches and shorter whistles produce higher pitches. Some whistles have a ball inside the chamber, often made of cork or synthetic cork, that bounces around, further disturbing the molecules to create a trilling effect. Steam whistles use steam to propel the air, which can make them quite loud.

Related Articles

Sources of Sound Energy
How Tone Generators Work
How Does Humidity Affect Speed of Sound?
How to Make a Cardboard Guitar for a School Project
What Experiments Can Be Done to Amplify Sound?
How to Tell Male from Female Crickets
Music Experiments for Kids
Sound Wave Science Projects
Piano Science Fair Ideas
How Does a Paper Cup Phone Work?
What Are Areas of Compression & Rarefaction in Waves?
Objects That Absorb Sound
Why Do Glass Cups Make a Ringing Noise?
Science Projects With Balloons & Sound Vibration
What Is the Decibel Level of a Jet Plane?
How Does Water Affect Sound?
Sound Wave Experiments for Kids

Dont Go!

We Have More Great Sciencing Articles!