Whistles are simple machines with few or no moving parts. In most cases, the sounds they make are activated entirely by air pressure, produced by nothing more than a human breath. Blow into a whistle softly and it makes barely a sound, but put your lungs into it and you will produce a screech that's attention-getting enough to stop most people in their tracks. How a whistle produces a sound is tricky to explain, but it goes something like...Continue Reading