What is the Speed of Sound?

R. Kayne

The speed of sound varies depending on altitude, temperature and the medium through which it travels. For example, at sea level in a standard atmosphere, at a temperature of 59-degrees Fahrenheit (15 Celsius), sound travels 761 miles per hour (1,225 km/p/h). At a temperature of 32-degrees Fahrenheit (0 Celsius) the speed of sound drops to 742 mph (1,194 km/p/h). In altitudes above sea level the speed of sound is again different and will vary depending on prevailing factors.

A jet breaking the sound barrier.
A jet breaking the sound barrier.

The reason for this variance is that sound waves travel by exciting molecules. When a sound wave hits a molecule it will vibrate, thereby transferring the vibration to adjacent molecules, which pass it on in a like manner. If molecules are packed very tight, the sound wave can travel very fast, increasing the speed of sound. When molecules are not as densely packed the speed of sound slows.

The advanced F-22 Raptor can achieve and sustain supersonic speeds without having to ignite its afterburners.
The advanced F-22 Raptor can achieve and sustain supersonic speeds without having to ignite its afterburners.

Temperature and altitude affect atmospheric density, changing the speed of sound. Sound will also travel faster through water than through air, because water is a denser medium. Likewise, sound travels faster through steel verses lower-density materials like wood, or atmospheric conditions. For this reason you might see an old movie depicting someone putting an ear to a railroad track to listen for an approaching train, as sound will reach the listener faster through steel rails than by air.

When a jet travels faster than the speed of sound, it is said to break the sound barrier. This creates a shock wave or sonic boom and an instantaneous “shroud” around the jet. The shroud is actually a white vapor cloud, which when caught in fast-speed photography, makes the aircraft appear as if it is emerging from a white wormhole.

Mach 1 refers to breaking the initial sound barrier, or going from subsonic to supersonic speeds. Military jets routinely travel supersonically. When a jet travels twice as fast as the speed of sound, it is traveling at Mach 2. Three times faster than sound refers to Mach 3, and so on.

If molecules are packed very tight, sound waves can move quite fast.
If molecules are packed very tight, sound waves can move quite fast.

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Discussion Comments


What is the number to break the speed of sound?


Speed of sound vs speed of light. Sound propagates through a medium (liquid, solid, gas), and the properties of those media determine the actual speed. Simply put, the denser the material the faster the sound waves travel. The speed of sound through air at ground level is approximately 760 mph, or approximately 1100 feet per second. The old lightning/thunder trick offers a good example. For approximately every five seconds the sound travels is one mile. See a flash of lightning then start counting. We've all done it!

In water, sound travels approximately 4800 feet per second, more than four times faster than in air. Also, one can assume that if there is no media to transmit the wave then there is no sound. (think about that one!)

Light, on the other hand, is an electromagnetic force. It has a constant and finite speed of 186,000 miles per second. May scientific calculations are based solely on this number alone.


@mexicana: As airplanes went faster and faster, the design of the wings created stresses that caused both loss of control and structural failure at the transition to speeds higher than the speed of sound. That is why they changed to delta shaped or swept back wings.

The planes didn't explode; they just broke apart.


How is the speed of light related to the speed of sound?


Isn't it amazing how God created everything so perfectly, like sound waves, even down to the tiniest detail? Even the smallest bone in the body, located in the ear. Our God is truly amazing and awesome.


How fast can sound waves travel at the absolute zero?


@mexicana: if an airplane flew faster than the speed of sound it won't explode. as a matter of fact, there are airplanes that are super sonic, which means faster than sounds and they can break sound barriers.

@danmurray: speed of sound is measured in terms of mach.


@anon98802: Air also becomes thinner the higher you go, @danmurray: amps a decibels are used to measure sound not its speed. meters is a length measurement. it's measured in MPH or KMH.


I believe that the speed of sound is only dependent on temperature and nothing else. As altitude increases, temperature decreases, thus the decrease in the speed of sound.


How is the speed of sound measured ? In Amps, Decibles, or Meters?


People used to actually believe that if an airplane flew faster than the speed of sound, it would explode!

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