# How to measure the speed of sound

Here is a great experiment to measure the speed of sound.

## Equipment needed to measure the speed of sound

You will need the following items in order to measure the speed of sound:

1 50M tape measure (50 metres is very long so if you haven't got one, make a measure by getting a ball of string and measuring out 50 one metre sections. Mark each one with a bit of coloured tape.)

1 stopwatch

1 big flat outdoor wall that produces a good echo

1 friend

## Measure the speed of sound

Use the tape to measure a distance of 50 metres from the wall.

Now clap your hands and check you can clearly hear an echo from the wall. Make sure the echo isn't coming from other walls in the area. The time it takes sound to run 100 metres is the time difference between when you clap and when you hear the echo.

However measuring that single short burst of time is difficult.

Now clap repeatedly in time with the echo, so that you can only hear your own clap (the echo is masked by your next clap)

So we can now measure the time it takes to clap 10 times. Start the stopwatch at the first clap and end it when you hear the echo of the 10th clap

We now know how long it takes for sound to travel 1 kilometre. A little bit of maths will let us convert that into Kilometres per hour or miles per hour.

### The actual speed of sound

The official speed of sound is 340.29 metres per second. Did your calculations come close?

### Faster than the speed of sound

There are a surprising number of things that move faster than the speed of sound:

Chuuck Yeager first broke the sound barrier in the Bell X-1 rocket plane in 1947.

A vehicle called the ThrustSSC (Super Sonic Car) became the first land vehicle to break the sound barrier in 1997.

When you crack a whip the tip often breaks the sound barrier.

Concorde was the only passenger aircraft (so far) to break the sound barrier.

The first flight at more than twice the speed of sound (MACH 2) was in a Douglas D-558-2 Skyrocket piloted by Scott Crossfield in November 1953.

The first flight at ten times the speed of sound (Over 7,500 miles per hour) occurred in November 2004. The aircraft was an X-43A but it was computer controlled rather than piloted by a human being.

The international space station orbits at 17,227 miles per hour.