Whistles can take a number of shapes and forms. They can be made from different materials, such as metal, wood or plastic. Even the pipes in a pipe organ are essentially whistles. Despite these differences, basically all whistles work alike. What happens when air is blown into a whistle is a complicated mathematical equation. But here are the basics. Air enters the whistle at one end. As the air reaches the other, closed end, all the air molecules "pile up" on top of each other and cause a high-pressure region. The air escapes out the little hole in the end, making the noise you hear. The frequency of the sound is dependent on the length of the whistle. The longer the whistle, the lower the pitch will be. The ball inside the whistle is not necessary for the whistle to work but serves a purpose. A whistle without a ball has a flat tone that may get "lost".
In an American Whistle the ball rises and falls as it is pushed around by the turbulence. When the ball moves within the chamber, it creates variations within the pitch, or the trilling sound you associate with a quality whistle blast. This variation is what catches your ear to the whistle alarm. Despite common terminology, the ball contained in pea whistles is actually made of cork. American Whistle Corporation has developed a synthetic cork material that behaves like natural cork in every respect except that it does not absorb any moisture. This prevents the ball from getting stuck inside the whistle and not swirling freely. And because the ball is moisture repellent and doesn't expand and contract, it lengthens the life of the whistle. A metal whistle delivers a louder blast than whistles made from other materials, such as plastic, which deadens sound. Whistles from the American Whistle Corporation are made from solid brass, the same metal that musical instruments are made from. We could use some other metal, such as steel, which would be less costly. However, brass amplifies sound, has excellent resonance and a musical quality that produces the best sound while creating a durable tool.