How Fast Does Sound Travel Per Second?

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

Have you ever watched a thunderstorm roll in, seen a brilliant flash of lightning, and then counted the seconds before hearing the rolling boom of thunder? That familiar delay is one of the easiest ways to witness physics in action. Light travels almost instantaneously to your eyes, but sound takes its time traveling through the air to your ears.

So, exactly how fast does sound travel? In standard conditions, sound races through dry air at roughly 343 meters per second (about 1,125 feet per second).

Translated into everyday driving terms, that is roughly 1,235 kilometers per hour or 767 miles per hour—faster than most commercial jet airliners! But that number isn’t a universal constant. The speed of sound actually changes depending on what it is traveling through.

Sound Speeds Across Different Mediums

Sound is essentially a wave of vibrations passing through a physical medium. It needs particles to bump into each other to propagate; because of this, sound cannot travel through the vacuum of space.

The tighter and more closely packed the molecules are, the faster those vibrations can jump from one to the next. That is why sound travels significantly faster in liquids and solids than it does in gases like air.

| Medium | Temperature | Speed (meters per second) | Speed (miles per hour) |
| :— | :— | :— | :— |
| Air | 20°C (68°F) | 343 m/s | 767 mph |
| Water | 20°C (68°F) | 1,482 m/s | 3,315 mph |
| Steel | Room Temp | 5,960 m/s | 13,332 mph |

As you can see, sound travels more than four times faster in water than in air, and nearly seventy times faster in steel!

What Slows Sound Down or Speeds It Up?

Even within the same medium, environmental factors can give sound a boost or slow it down:

• Temperature: In gases like air, temperature is everything. Warmer air means molecules have more kinetic energy and are bouncing around faster, which helps sound waves move more quickly. Cold air, on the other hand, slows sound down.
• Humidity: Surprisingly, humid air is actually less dense than dry air (water vapor is lighter than nitrogen and oxygen molecules). Because the air is less dense, sound waves travel slightly faster in high humidity.
• Altitude: As you climb higher in the atmosphere, the air gets colder. This drop in temperature causes the speed of sound to decrease the higher up you go.

Breaking the Sound Barrier

When an aircraft accelerates until it matches the speed of sound, it reaches Mach 1. As it pushes past that threshold, it creates a massive compression wave of air molecules piling up in front of the vehicle.

When the aircraft finally breaks through this wall of compressed air, it produces a loud, explosive shockwave known as a sonic boom. To people on the ground, it sounds like a sudden thunderclap, even on a completely clear day!

A Quick Trick to Remember

Next time you see a lightning flash, count the seconds until you hear the thunder. Divide that number by 3 (if counting in seconds per kilometer) or 5 (if counting in seconds per mile), and you will have a remarkably accurate estimate of how many kilometers or miles away the storm is!