What if sound traveled through water?

When you clap, the sound goes through the air to your ears.

But whales call to each other under the sea. Can sound go through water too?

Most sounds you hear have traveled through air: a voice, a dog's bark, a clap of thunder. But the ocean is full of sounds too. Whales sing, dolphins click, and waves crash.

So what happens when a sound travels through water instead of air? Does it go slower, faster, or not at all? In this lab you can send the same sound the same distance through air and through water, and time it.

Sound is a mechanical wave: a compression passed from particle to particle. It needs a medium, and the medium sets its speed. Air, water and steel all carry it, at very different speeds.

This lab asks a simple question with real consequences for ocean life and ocean science: how does the trip change when the medium is water? The model sends a single sound pulse 1,000 meters, first through air at 20 °C and then through fresh water.

In air, sound is fast. But it still takes a little time.

In Olly's lab, a sound takes about 3 seconds to go 1,000 meters through air.

In air, sound moves at about 343 meters every second on a warm day. That is fast, but you can still notice the wait over long distances. It is why you see lightning before you hear the thunder.

In our model, a sound sent 1,000 meters through air at 20 °C takes 2.91 seconds to reach the listener. Count it out: one, two, almost three.

In dry air the model uses c = 331.3 √(1 + T/273.15) m/s, which gives 343 m/s at 20 °C. A pulse covering 1,000 meters therefore arrives after 2.91 seconds, and 2,000 meters takes 5.83 seconds.

Pitch does not change the speed. A 440 Hz note (the A that orchestras tune to) has a wavelength of 0.78 m in air, because λ = c/f. OpenStax lists 331 m/s at 0 °C and 343 m/s at 20 °C, matching the model.

Now Olly sends the sound through water.

Whoosh! It gets there much faster. Sound zooms through water.

Now switch the medium to water and send the same sound the same 1,000 meters. This time it arrives in just 0.675 seconds, less than a quarter of the time it took in air.

The model's speed readout jumps from 343 to 1,481 meters per second: 4.3 times faster than in air. In one second, sound in water can cover 1,481 meters, almost one and a half kilometers.

With the medium set to water, the model uses a fixed 1,481 m/s, the speed in fresh water at 20 °C. The 1,000 m trip shrinks from 2.91 s to 0.675 s, and the speed ratio readout shows 4.3×. Over the slider's full 2,000 m the times are 5.83 s in air and 1.35 s in water.

The wavelength grows in the same proportion: a 440 Hz note stretches from 0.78 m in air to 3.37 m in water. For comparison, the model's steel setting carries sound at 5,960 m/s, 17.4 times faster than air.

Sound is a push that goes from one tiny bit to the next.

Water is very hard to squash. So it passes the push along quickly.

Sound is a push passed along from one tiny particle to the next. How fast the push travels depends on how hard the material is to squash. Air squashes easily. Water is much harder to squash, so it pushes back quickly and passes the sound along faster.

Our model is simple. It uses fresh water at one temperature and sends the sound in a straight line. It does not show how loud the sound is, how it fades or how it bends in the real sea.

The speed of a sound wave is c = √(K/ρ), where K is the medium's bulk modulus (its resistance to compression) and ρ its density. Water is far denser than air, but it is so much less compressible that c is larger. OpenStax puts it simply: the more rigid, or less compressible, the medium, the faster the sound.

Model limits: a single fixed speed for fresh water at 20 °C, a straight path, no echoes, no bending, and no loudness or fading. Seawater is faster (OpenStax lists 1,540 m/s at 20 °C), and its speed changes with depth, which the model cannot show.

Humpback whales sing long songs in the sea.

Their songs can travel for miles. Scientists listen with underwater microphones.

In the real ocean, the University of Rhode Island's DOSITS project says sound moves at about 1,500 meters per second, a little faster than in our fresh-water model. Its speed changes slightly with temperature and depth.

NOAA explains that how far a sound goes depends mostly on temperature and pressure. Deep down, a layer called the sound channel bends sound waves up and down so they can travel hundreds of miles. In Hawaii, NOAA says male humpback whale songs can carry over several miles, and scientists record them with underwater microphones called hydrophones.

DOSITS gives about 1,500 m/s for seawater, varying by a few percent with temperature, pressure and, less often, salinity. Near the surface, cooling with depth slows sound; deeper, rising pressure speeds it up. The resulting speed minimum, at roughly 1,000 m in mid-latitudes, forms the SOFAR channel: sound bends back toward it from above and below and can travel thousands of miles without losing much energy (NOAA).

NOAA notes that whales use this channel to communicate over hundreds and even thousands of miles, and that ship noise can interfere. Speed matters for timing; distance depends on the channel and on how little energy low sounds lose.