Most people, whether they are students or workers, have a pretty clear idea of how sound works. After all, who hasn’t heard about sound waves, vibrations, and other similar concepts? Yet, there are a few notions that still baffle people to this day, particularly regarding the way sound propagates in water and air. And, with so much contradictory information online, it’s easy to see why.
So, if you’re one of the many who want to know if sound travels faster in water or air, this article has got you covered. But first, let’s start with the basics!
What Is Sound?
Generally speaking, sound is a type of longitudinal mechanical wave that travels through a medium. However, there are two definitions regarding how sound is produced.
For starters, in physiology, sound is created when an object’s vibrations travel through a medium until they reach the human eardrum. In physics, sound is produced in the form of a pressure wave. More specifically, when objects vibrate, they cause the nearby molecules to also vibrate, triggering a chain reaction of sound wave vibrations in the specific medium.
But no matter which definition you prefer, you’ll notice a similarity — sound needs a medium to propagate and will not travel through a vacuum. As a matter of fact, sound travels at different speeds depending on the medium. In other words, the medium’s density and compressibility directly affect the speed of sound. For instance, sound waves will travel slower in a less dense and more compressible medium.
How Fast Does Sound Travel in Water?
When it comes to water, sound can travel as fast as 1,498 meters per second, or approximately 3,350 miles per hour. However, as mentioned earlier, the physical characteristics of the medium highly affect the speed.
As a result of its high salinity, seawater, such as oceans, allows sound to travel up to 33 meters per second faster than the freshwater found in lakes. That’s because salt molecules respond quickly to the disturbances of neighboring molecules, propagating sound waves faster and at longer distances.
The speed of sound is also dependent on density. As you might already know, water has an impressive density due to its unique molecular arrangement. Thus, sound waves can travel much faster underwater as the wave bumps and vibrates with more molecules.
Temperature and Pressure
You need to understand that, as the ocean gets deeper, its temperature decreases and its pressure increases. These affect the particle arrangement and, by extension, the speed of sound. To put it simply, sound travels slower at the surface level than at lower depths.
How Fast Does Sound Travel in Air?
Sound is able to travel through the air at an average of 332 meters per second, or 742 miles per hour. Although that might seem fast, it is not nearly as fast as light, which travels at 186,411.358 miles per hour. But as with water, there are also many factors that affect how sound propagates in the air:
Air molecules tend to have more energy at higher temperatures, meaning that they will vibrate faster. That allows sound waves to also travel faster and farther, as they are propelled by molecule collisions. Yet, as the sound moves through the atmosphere, some parts of its wave will travel faster than others due to temperature differences.
What’s interesting about sound is that, at a constant temperature, its speed is not dependent on the pressure of the medium. That’s because these two properties are tied to one another. So, increasing temperature will also increase pressure and, consequently, the speed of sound.
The wind direction can impact the speed of sound and the distance it can travel. In fact, you might notice that sound levels are higher when the wind is blowing down, such as from a highway towards the ground level.
Water vapors are less dense than dry air at a constant temperature. Naturally, the presence of moisture will decrease the air’s density and increase the speed of sound. Therefore, humid environments experience much faster sound propagation than dry and cold areas.
Why Does Sound Travel Faster in Water Than Air?
By now, you might have noticed that sound travels about four times faster in water than in air. The main reason behind this is that water is denser than air. Sure, not all water has identical properties, as salinity and temperature vary and affect its density. But even so, molecules in the water are closer together, causing more vibrations to be transmitted at a faster speed of sound.
Furthermore, water is an incompressible environment. Actually, it’s better to imagine water as being similar to a solid object, as they tend to behave similarly when it comes to compression. More specifically, when water encounters a force, it will immediately transfer its energy to nearby molecules, just like solids. This characteristic is partially offset by the water’s high density, creating the perfect environment for sound to travel through.
And lastly, it’s important to mention that sound travels faster in harder materials. It’s true that water as a unit is not necessarily hard; however, it has a strong bond between its molecules. Hence, the propagation of sound is faster as it passes more quickly from one particle to the next.
But Why Is It Harder to Talk to Someone Underwater?
Naturally, you might assume that, since sound travels faster in water, it would be incredibly easy to chat with someone while swimming or diving. But that couldn’t be further from the truth.
When someone talks, they do so by emitting air and sending compression waves through it. That’s thanks to your lungs, vocal cords, and mouth, which work together to imprint a sound waveform on the burst of air that comes from your body. So, in order for someone that’s in the water to hear you, the sound will need to travel from your mouth into the surrounding water.
However, sound couples very poorly from air to water. As a matter of fact, water tends to reflect external sound waves instead of allowing them to penetrate its surface. That’s also the reason why phenomenons like echos occur when you scream or talk near a well, as the water at its bottom reflects the sound waves back to you.
What About Sound Travel Distance?
When it comes to sound travel, water is again the clear winner, as it allows sound to propagate to distances of almost 15,500 miles. To understand why that’s the case, imagine a whale that is swimming through the ocean and calls out to its peers. The sound waves it produces move similarly to ripples in the water.
As the sound travels and reaches increasing depths, it begins to slow down and eventually refracts downward. Once the sound reaches a region called the thermocline layer, its speed further decreases to a minimum. That’s because the thermocline layer features rapid changes in pressure and temperature.
After breaking through the layer, sound waves encounter another area where the temperature remains constant. However, the pressure continues to rise, which causes a boost in the sound speed, making it refract upward. This channeling of waves allows the sound to travel thousands of miles with little to no energy loss. It’s thanks to this process that scientists can pick up whale songs from many miles away.
Understanding how sound works and travels is extremely important. Sure, you might not deal with mediums like water every day. However, air is all around you, and learning the way it affects sound speed can help you figure out the perfect way to soundproof your environment and enjoy a noise-free life!
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