Why does sound travel faster in water than in air?

• 2026-08-16
• Sains
• Meja Berita
• Source: uk.euleader.org

Sound travels through the air at a speed of about 343 meters per second. In fresh water, similar waves travel at a speed of about 1480 meters per second, in sea water – about 1520. In this article, Rambler will tell you what causes this difference. What is sound from a physical point of view?

Sound is a mechanical wave, the sequential compression and rarefaction of a medium. As the speaker cone moves forward, it compresses the air molecules in front of it, creating an area of ​​increased pressure. This region transmits the impulse to neighboring molecules, which then transmits the impulse to the next molecules – and so on along the chain. The molecules themselves don't fly anywhere. They vibrate in place, and only the turbulence—the pressure wave—is in motion.

The rate at which this perturbation is transmitted from one particle to another is determined by two competing properties of the medium: elasticity and inertia.

The first speeds up the transmission, the second slows it down. Mathematically, this is expressed by the Newton–Laplace equation: c = √(K / ρ) c is the speed of sound, K is the bulk elastic modulus, characterizing the compression resistance of the medium, ρ is its density, its inertial force with respect to motion.

NASA is testing quiet hypersonics: how it will change aviation Elasticity versus inertia It is this relationship that explains the apparent paradox of water.

The density of water is about 830 times the density of air, which alone slows sound in water about 29 times. However, the elasticity of water is much higher. The bulk modulus of water is about 2.2 GPa, while the modulus of air is about 142 kPa, meaning water is about 15,600 times harder to compress. The water molecules are so tightly packed that pressure disturbances are transmitted from one place to another with almost no delay.

On the other hand, air molecules are separated by large gaps and only interact through random collisions, making transmission take longer. If we substitute both parameters into the formula, the increase in elasticity compensates for inertia losses by a large margin. The final acceleration is √(15,600/830) ≈ 4.3 times – exactly what is observed in reality.

Three factors affect the speed of sound in water In real oceans, the speed of sound is not constant. It varies depending on three physical parameters each dosage describe quantitatively. Temperature – the most important factor in the upper layers.

For each degree Celsius increase in temperature, the speed of sound in seawater increases by about 4 m/s. This is why the surface layers of warm tropical waters conduct sound faster than cold Arctic waters.

salinity has a moderate effect: increasing the salt concentration by 1 PSU unit will increase about 1.3 m/s. Sodium and chlorine ions dissolved in water enhance interactions between molecules and increase the elasticity of the medium. Pressure (depth) different actions. As depth increases, pressure compresses the water, reducing the distance between molecules and increasing elasticity. This adds about 1.7 m/s for every 100 meters of depth. SOFAR channel: natural waveguide The three factors – temperature, salinity and pressure – act simultaneously in the ocean, but differently depending on depth.

At an altitude of about 1000 meters, the water becomes so cold that the temperature stops accelerating the sound, but the pressure is still not high enough to compensate. As a result, a layer with a minimum sound speed is formed – the SOFAR channel (Sound Fixed and Separated Channel), which NOAA described as a natural “waveguide” of the ocean. Sound waves entering this layer behave like light in an optical fiber.

When they deviate up or down from the minimum speed zone, they immediately enter a faster environment that brings them back up. The waves move along the axis of the channel without scattering to the sides and with minimal energy loss. In the spring of 1944, American scientists Maurice Ewing and J. Lamar Warzel were the first to experimentally confirm this effect.

Explosions falling to a depth of about 450 meters were recorded by hydrophones at distances of up to 900 nautical miles, which is about 1,650 kilometers, reports Explore sounds in the sea. Blue whales and fin whales use SOFAR to communicate over transoceanic distances.

Their low-frequency signals partly fall into this layer and spread throughout it for thousands of kilometers. Therefore, the high speed of sound in water is a consequence of a fundamental relationship: the elasticity of the medium is more important than its inertia. Water is 15,600 times harder to compress than air, and this difference in hardness implies an 800-fold advantage of water in density.

We previously wrote about whether there is sound in space.