Planet Science Out There

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sound check... what is sound?


KER-BOOM!

What was that??

From the biggest explosion…
to the smallest rustle of a leaf…
to the noise of your neighbours watching ‘Last of the Summer Wine’ at top volume…

Sound is all around.

Most people figure out how to make a sound very early in life.But have you ever wondered what sound actually is and how it works?

If so, you’ve come to the right place…

Good Vibrations

Hummingbirds don’t know much about history.


They don’t know much about biology. and most can’t speak french.
But they can teach us quite a bit about sound.

EXPERIMENT:

a) If you’re a hummingbird, start to flap your wings as fast as you can.

b) If you’re a human being, start to flap your arms as fast as you can. (CAUTION: This may not work as well and there is a major risk of looking uncool.)

As your wings (or arms) flap faster and faster - at least 20 times a second - they make the air around them vibrate backwards and forwards. And hey presto...a lovely sound is produced.

Fortunately flapping isn’t the only way to produce sound. Anything – or anyone – that can make vibrations in the air will create sound.

Want to see the vibrations that cause sound? Learn how to make some particularly good ones? Or perhaps stop them in their tracks? Then check our our Top 10 of best-ever sound activities.

Plucking a string on a violin makes the air vibrate and creates a sound.

Clapping your hands makes the air vibrate and produces a noise.

Your vocal cords enable you to speak and sing.

Twanging the elastic on a pair of pants can make various sounds (try it).

And a hummingbird playing an electric guitar and singing would make an amazing sound. (Hummingbirds are notoriously bad at remembering song lyrics though. That’s why they hum.)

Sound is created by ANY vibration that makes the particles of the air wobble back and forth.

The wobbling particles shake the particles next to them, which also vibrate, shaking the next particles and so on. And these rippling waves of air travel to your ear, where your brain makes sense of them as sound.

In this way, these vibrations are a bit like the ripples on a pond when you throw a stone in.

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In space no one can hear you scream

question:

If vibrations travelling through the air cause sound, what happens when there’s no air?

answer:

a) You can’t breathe. And
b) There’s no sound.

Which means that if there were a planet somewhere with no air, it would be a very, very quiet place, and the inhabitants would have to communicate using some other method (perhaps using speech bubbles?)

Here on Earth, you may have noticed that there’s plenty of air, and so plenty of sounds. Sounds can also travel through liquids (fish have ears too!) and solids. Again, it’s the vibrating particles that carry the sound waves.

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‘Hertz’ that sound and sounds that hurt

So if all sounds are just waves of vibrating air particles, why don’t they all sound the same?


One reason is that different sounds are produced depending on how many times the air vibrates every second. This is called the ‘frequency’ of the sound and is measured in Hertz (Hz).

High-pitched sounds have a high frequency. Low-pitched sounds have a low frequency.

Try using the PS100X Sound Sampler to hear notes at different frequencies.

Lower frequency sounds are able to travel further than high frequency ones – which is why if there’s music playing at a distance, you’ll hear mostly the bass tones.

The lowest sounds humans can hear are about 20 Hz (anything below is called infrasound). And we can’t hear sounds above a maximum of 20 000 Hz (higher sounds than that are called ultrasound).

Many animals, such as bats and dogs, can hear higher-pitched sounds than we can. And if you’re lucky enough to be an elephant you’ll be able to hear sounds as low as 5Hz. (Though if you’re an elephant you’re probably having difficulty using the mouse.)

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Pump it up! Turn it down!

Big vibrations create loud sounds and small vibrations make soft sounds, so size matters.


The loudness of a sound is measured in ‘decibels’ (dB).

0dB would be the quietest thing you could ever hear, while listening to anything over 90dB for too long could damage your hearing. Sounds over 130dB will cause you physical pain.

Drawing Sounds

We can draw a sound wave as a simple picture like this.

Diagram of a sound wave
The bigger the peaks and troughs (or ‘amplitude’) of the wave, the louder the sound is. And the closer together the peaks and troughs are, the higher the frequency (and therefore the pitch) of the sound.

Check out the PS100X Sound Sampler where you can modify sounds, even ones you record yourself!

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The need for speed

The speed of sound through the air is 330 metres per second. That’s faster than a cheetah who’s just sat on a drawing pin…


In warmer air, the speed of sound increases, and it increases even more in denser materials. In water it travels at 1500 metres per second, and in in solid objects it’s faster still - for example in steel it’s 5200 meters per second.

Although this sounds fast, it’s not so fast that you can’t notice some interesting effects.

I sync therefore I am…

Next time there’s a huge thunderstorm, you could either:


a) Hide under your duvet cover

b) Work out how far away the storm is using the science of sound

You probably don’t need any help with the first one, but here’s how to do b…

The light from the lightning will reach your eyes virtually instantaneously. But sound, as we know, travels relatively slower, at roughly 330metres per second. So if you count how many seconds pass after a lightning flash until you hear the thunder, and multiply this by 330, you’ll know how metres – or kilometers - away the storm is.

This is the same principle that explains why, if you’re watching a concert from the back of a stadium, you can see the lips of the singer move a split second before you hear the words. Either that or the singer's really bad at miming.

Neee-nawww

You can hear another interesting sound effect when you listen to an ambulance drive past you. As it approaches the siren sounds quite different to when it has passed.


What’s happening is that as the ambulance approaches, the sound waves coming towards you are more squashed together, because the vehicle’s travelling in the same direction as the waves it’s emitting, so the frequency (and pitch) sounds higher. As the ambulance drives away from you, the sound waves are more spread out which is why they sound lower. This is called the Doppler effect.

Sonic boom boy…

No one knew whether it was possible for humans to travel faster than the speed of sound

- and survive -


Until American pilot Chuck Yeager did both and became the first person to break the ‘sound barrier’ in 1947.

Today many military jets are able to fly at supersonic speeds.

If you were to see a supersonic plane fly overhead, you’d hear a deafening bang called a ‘sonic boom’ as it breaks the sound barrier.

This is caused by the aircraft trapping air into a cone-shaped shock wave, which hits the ground and makes a loud boom.

If a passenger on board an aeroplane was able to shout ‘hello’ to you as they were flew at supersonic speed towards you, the plane would reach you before the words did!

(On board however, you could hold a normal conversation as you’d be travelling supersonic speeds as well!)

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