Whistle is a device that makes a sound when air or steam is forced through it. Most whistles consist of a tube that has a hole in its side with a lip or a sharp edge on it. The air or steam that is blown in one end of the tube goes into a swirling motion when it strikes the lip. This motion first compresses and then expands the air, causing a sound.
Steam whistles are seldom used today. Steam locomotives once used them. But today’s diesel locomotives use various types of air horns, some of which sound like steam whistles. Police officers and sports officials blow small air whistles.
