Why We Whistle
People can make a whistling sound by pursing their lips and blowing a stream of air from the mouth. This generates vibrations that create the high pitched sound. If fingers are placed strategically in the mouth before blowing, a louder sound can be produced. Devices are also used to make whistling sounds, from the train's loud steam whistle to the teacher's pea whistle on the school playground. Whistles can produce a varying range of pitches and volume.
Whistles can be made of a hard material, such as plastic, wood or metal. It is a device that makes a whistling sound when air is blown through its mouthpiece. One type of whistle is similar to a hollow tube, where one end is open and used as the mouthpiece. On the side of the whistle is a sharp edge that creates a slit or opening along the midsection. When air is blown into the opening, it strikes the edge which sends the air whirling. This motion compresses and then expands the air. That creates vibrations and makes the trademark whistling sound.
Trains and other forms of transportation used a loud whistle in the same way as a car uses a horn. This was typically a steam whistle, which worked on the same principle as the tubular whistle that we blow into. Yet, instead of manually puffing air into the steam whistle, a burst of steam is forced through the whistle. That creates a louder and far reaching whistle sound.
The type of whistle typically used by teachers and sports coaches is a pea whistle. The pea whistle contains a small ball in its chamber. When air is blown into its mouthpiece, it sends the ball whirling inside. The familiar teacher's pea whistle has a narrow, flat rectangular tube that is its mouthpiece. That is connected to an end that is shaped like a barrel. This barrel holds the whistle pea. An air slot is at the section where the tube connects to the barrel portion. When air is blown into the narrow mouthpiece, it moves down the tube and encounters the edge of the slot. That slot slices the airflow into two. The top portion moves upwards in a curl and forms a swirling vortex of air, causing vibrations. This generates a sound. The air that moves into the barrel swirls around the inner walls and creates vibrations and sounds.
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