Shepherd's whistle
They are also produced commercially. Simple whistles may cost less than 1 USD in bulk; expensive ones may be quite ornate. They are commonly made of plastic, aluminum, stainless steel, silver, brass, titanium, Corian, jade, buffalo horn and other materials.
Physics of whistles
A whistle is a device that makes sound from blowing air. The physical theory of the sound making process is an example of the application of the science of fluid dynamics. Knowledge of the geometry, dimensions and fluid properties can allow prediction of the properties of the whistle. The principles relevant to whistle operation also have applications in other areas such as fluid flow measurement.