Speed of Sound
Think of people standing shoulder-to-shoulder in a line, tapping the next person to pass a message along.
Definition The speed of sound is the rate at which sound vibrations travel through a medium, such as air, water, or solids. Because sound moves by particles bumping into each other to pass along vibrations, its speed changes significantly depending on the material and its temperature.
Why You See Lightning Before You Hear Thunder
During a storm, you have probably noticed a flash of lightning followed several seconds later by a rumble of thunder. Lightning and thunder happen at the exact same instant inside the storm cloud, so why don't they reach us together?
The reason is that light and sound travel at completely different speeds. Light travels at an unimaginable speedโcircling the Earth about seven and a half times in just one secondโwhile sound in air creeps along at only about 340 meters (roughly 1,120 feet) per second.
If you count three seconds between the flash and the rumble, that lightning struck about 1 kilometer (roughly 0.6 miles) away. Even though sound is invisible, it acts like a courier sprinting through the air at a steady pace.
Sound Travels Much Faster in Water and Steel
In the vacuum of outer space, no matter how loud you scream, sound cannot travel at all because there are no air molecules to carry it. The giant explosion sounds in space movies are scientifically impossible!
Sound is a vibration where particles bump into neighboring particles and bounce back. This means the closer together the particles are packed, the faster they can pass the vibration down the line.
In water, where molecules are packed much closer than in air, sound travels about four times faster. In dense solids like steel or iron, it travels roughly 15 times faster than in air. This is why characters in classic Western movies would press an ear against the metal train tracks to hear an approaching train long before hearing it through the air.
Temperature Changes the Speed of Sound, Too
People often assume that 340 meters per second (about 761 mph) is a fixed constant for the speed of sound. However, the speed of sound in air actually shifts with the surrounding temperature.
When air gets warmer, air molecules absorb thermal energy and bounce around much faster. Because the molecules are already zipping around quickly, they collide with their neighbors sooner, speeding up the transmission of sound vibrations.
At 0ยฐC (32ยฐF), sound travels through air at about 331.5 meters per second, increasing by roughly 0.6 m/s for every 1ยฐC rise in temperature. The familiar benchmark of 340 m/s is actually based on a mild air temperature around 15ยฐC (59ยฐF).
๐ค Common misconceptions
Sound travels at the exact same speed everywhere and at all times.
The speed of sound constantly changes depending on the density and elasticity of the medium (air, water, solids) as well as the ambient temperature.
A massive planet exploding in outer space would create a deafening roar.
Sound requires particles to transmit vibrations; in the vacuum of space, where there are no air molecules, sound cannot travel at all.
๐งบ Where you meet it
Sound travels through vibrating particles, moving faster through tightly packed solids and in warmer air temperatures.