The origins of the modern whistle
Manufactured whistles are made of either metal or plastic. The only metal whistles manufactured in the United States are made of brass...the fact that they are nickel or chrome plated gives rise to a common misconception that they are made of steel (Hall).
The majority of whistles manufactured today are made of metal, specifically brass. This metal is actually an alloy of copper and zinc that is formed by mixing the molten metals together and cooled, pressed flat, and bent into a hollow chamber with an opening where the air splits and creates vibrations that are heard as a whistle. The reason that brass is used is the same reason it is used in bells and other musical instruments. Its tone and resonance is superior to other metals because the zinc and copper together are both strong and able to vibrate at the perfect speed that creates smooth-sounding sound waves. Some whistles are plated with other grey metals, but these do not hinder its sound quality. Since almost all whistles are created out of the metals copper and zinc, the origin of the modern whistle was a supernova (a dying star that explodes), where all metals heavier than iron are created.
Brass is a metal used in many things because of its versatility. Other than for decorative purposes, it is used in many musical instruments, from wind instruments to bells. The reason for this is its excellent tone quality unmatched in any other metal. This is not a single metal, though; it is an alloy (a combination of two metals) of copper and zinc (with a negligible amount of lead sometimes mixed in). Pure copper or zinc would not have the same qualities, and even a small difference in proportion can either make the alloy break or bend too easily. However, by mixing the perfect amounts of each molten metal together, the brass created has outstanding resonance, which means that it vibrates at a frequency that produces a great-quality sound. The copper and zinc used to create whistles are forged inside a dying star. Scientists know this because during a supernova, hot enough temperatures are reached to create elements heavier than iron (including those used to make whistles).