Why does sound travel faster in water than in air?

Sound is not a thing that flies through space on its own. It is a vibration that passes from one particle to the next. When you speak, your vocal cords push on the air molecules around them. Those molecules bump into their neighbors, which bump into theirs, and so on, until the chain of nudges reaches someone else's ear. How fast that chain travels depends entirely on the material the sound is moving through.

In water, the molecules are packed much more tightly together than in air. They are practically touching. As soon as one molecule is nudged, it immediately bumps the next one, and the signal races along. In air, the molecules are spaced much further apart. Each one has to travel a comparatively long distance before it can pass the message on. The result is a real, measurable difference. The speed of sound in seawater is roughly 1,480 metres per second; in normal air it is about 343 metres per second — well over four times slower.

Closeness is not the only reason. Water is also far less compressible than air. When a sound wave passes through, the medium has to be able to spring back quickly to keep the wave moving. A stiff, hard-to-compress material does this very efficiently; a soft, easily squashed one does not. Air is easy to compress, so it absorbs and slows the vibration. Water resists compression, so it carries vibrations cleanly and quickly. This is why sound moves even faster through solids like steel than through water.

This is not a piece of trivia. It is the reason whales can communicate across vast distances of ocean using low-frequency calls — their sound waves travel huge distances quickly and clearly underwater. It is the principle behind sonar, where ships send out pulses of sound and use the time it takes the echo to return to map the seafloor or detect objects. And it is why noises feel strangely different to a swimmer with their ears below the surface: the same world is suddenly carrying its sound through a far faster, far more efficient medium.

This article was written using information from Wikipedia.