Can you blow a whistle underwater?

Answer 1

Not with the same effect as in the air. (There are special whistles designed to work underwater.)

The closed whistle (such the metal ones used in sports officiating) create vibration by compressing and releasing air. There are two ways it could be used underwater. If you blow air into a whistle underwater, it will make a whistling sound, but you would have to use enough air to force the water out of the whistle chamber, and the vibrations will be carried differently by the water. It will not carry into the air from any depth at all. If you blow water into a whistle underwater, the water stream will be divided, but the vibration created will not be at an audible frequency, because the liquid is not compressible.

How a Whistle Works

An ordinary whistle works by dividing a moving stream of air, so that one stream concentrates air into a chamber and releases it -- the chamber resonates as it releases the trapped air. A variation (pea whistle) uses a moving sphere within the whistle to strike the sides and create a more forceful vibration. In some Musical Instruments, such as a Flute, a reed causes vibration in the alternating air stream. In horns, it is the vibration of the player's lips, which is amplified by the metal horn body. A whistling sound outside a window (wind, moving vehicle) is similarly caused by escaping air.

To achieve a louder sound, "pealess" sports whistles use specially shaped chambers that concentrate the air flow.