# The Speed of Sound: How fast is it?

Question: What is the speed of sound?

• 1127 feet/second
• 343 meters/second
• 768 miles/hour
• 1236 kilometers/hour

Sound is a wave. It needs to travel through something in order to move. The speed to which it travels greatly varies depending on what substance it is traveling through. The denser the substance is, the faster the sound wave can travel through it.

• Sound travels 1127 feet/second through Air.
• Sound travels 3041 feet/second through Helium.
• Sound travels 4862 feet/second through Water.
• Sound travels 21063 feet/second through Aluminum.
• Sound travels 39400 feet/second through Diamond.

All of the above speeds are assuming that the temperature is 20°C (68°F).

In solids, the density of the material (not the temperature) affects the speed that sound travels through it. More solid substances like aluminum conduct sound faster than air.

Temperature affects the density of liquids and gases. The colder they are, the closer together the molecules become to one another. Because of this, one would think that as temperature in liquids and gases rise, the speed of sound through them would fall. However, this is not the case.

• Sound travels 4603 feet/second through Water at 0°C (32°F).
• Sound travels 4862 feet/second through Water at 20°C (68°F).
• Sound travels 5006 feet/second through Water at 40°C (104°F).
• Sound travels 5092 feet/second through Water at 60°C (140°F).

Speed of Sound vs Temperature in Dry Air

When we look at the speed of sound through gases and liquids at different temperatures, something interesting happens! When the temperature is increased, the speed that sound travels through it increases too. This is because in gases and liquids, higher temperatures cause the molecules to move faster (and have more energy). Therefore, they can vibrate faster and sound waves can travel more quickly through them.

• Sound travels 1009 feet/second through Air at -40°C (-40°F).
• Sound travels 1048 feet/second through Air at -20°C (-4°F).
• Sound travels 1087 feet/second through Air at 0°C (32°F).
• Sound travels 1127 feet/second through Air at 20°C (68°F).
• Sound travels 1166 feet/second through Air at 40°C (104°F).

Humidity in the air has a very little, yet measurable effect on sound speed.

Air pressure is often stated as a contributing factor to sound speed through air, however this is incorrect. Air density on the other hand is a contributing factor. The lower the air density the slower the sound travel will be. Although altitude has no effect on sound speed through air,  it does correlate with air density and temperature which do. As you go up in altitude/elevation, the air density and the temperature drop.

INTERESTING FACTS:

• In a vacuum where there is zero air density, there is no sound at all! This is because there is nothing for the sound waves to travel through.
• Volume does not affect the speed of sound.
• Frequency (Pitch: Bass, Mid, Treble) does not affect the speed of sound.

If you’re looking for more information about the speed of sound and how it’s affected by things, Wikipedia has some more great information.