How Fast Does Sound Travel Per Second?

The Speed of Sound: How Fast Does It Actually Travel?

Have you ever wondered how quickly sound reaches your ears when someone calls out to you from across a field? While light from a flash or spark is practically instantaneous, sound takes its time. In standard room-temperature air, sound travels at an impressive speed of 343 meters per second (about 1,125 feet per second or 767 miles per hour).

However, that number isn’t set in stone. The exact speed of sound depends heavily on what it is traveling through and how warm that environment is.

Breaking Down the Numbers

Depending on your preferred unit of measurement, sound covers ground at these speeds in dry air at 20°C (68°F):

• Meters per second: 343 m/s
• Feet per second: 1,125 ft/s
• Kilometers per hour: 1,235 km/h
• Miles per hour: 767 mph

Why Does the Medium Matter?

Sound is essentially a wave of vibrating particles bumping into one another. Because solids and liquids have molecules packed much tighter together than gases, sound vibrations pass through them much faster.

• In Air: ~343 m/s (gas)
• In Water: ~1,481 m/s (liquid, roughly 4.3 times faster than air)
• In Steel/Iron: ~5,120 m/s to 5,940 m/s (solid, nearly 15 times faster than air)

This is why, if you put your ear to a metal train track, you can hear an oncoming train long before you hear it traveling through the air.

The Temperature Factor

Temperature also plays a major role. In air, sound waves move faster when it’s hot and slower when it’s cold. This happens because warmer molecules have more kinetic energy and bounce into each other quicker, passing the sound wave along faster. For every degree Celsius the temperature drops, the speed of sound decreases by about 0.6 meters per second.

The Classic Lightning Trick

You have likely used the speed of sound in real life without even realizing it. During a thunderstorm, light travels at nearly 300,000 kilometers per second, meaning you see the flash of lightning instantly. Sound, however, takes roughly 3 seconds to travel 1 kilometer (or about 5 seconds to travel a mile). If you count the seconds between seeing lightning and hearing the thunder and divide by 3, you can easily figure out how many kilometers away the storm is!

Understanding the Speed of Sound in Air

This video provides a great breakdown of why sound travels at 343 meters per second in air and highlights the key physical factors that influence sound waves.
http://googleusercontent.com/youtube_content/1