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Finally one for you J. As love is friendship set to music, you've got the love I need to see me through.
A UNIVERSE FULL OF SOUNDS!
You might have come across the saying that in space no one can hear you scream, but do you know what that means? Or whether it is even true? In this book, you’ll discover the answers to these questions and many more about sound, space and nature.
Together, we’ll zoom across the stars, dive deep into the oceans and even drill far below ground to see how sound changes in different environments. We’ll find out how humans first started playing and recording music, listen for patterns in whale song, and discover whether mice really are as quiet as everyone says. We’ll be amazed by cutting-edge sound technology, learn why we see lightning before hearing thunder, and investigate eerie sounds at the bottom of the sea. And, when we get to space, we’ll wonder what aliens might sound like – and discover, once and for all, whether or not we can get music on the Moon!
But first, let’s find out a bit more about how sound works, how we hear, and why sound can make us feel certain things.
WHAT IS SOUND?
Vibrate means to move quickly back and forth.
Sound is a type of energy that is created when an object vibrates.
For example, when a person knocks on a door, it makes the door vibrate. The vibrations are too small for our eyes to see, but they cause the particles in the air near the door to vibrate too. These particles then cause the particles next to them to vibrate as well, setting off a chain reaction of vibrations!
Atoms are the basic building blocks of matter. They join together with other atoms – a bit like LEGO™ blocks! – to make up matter. For example, a piece of iron is a type of matter, and it’s made up of lots of iron atoms all joined together.
When two or more atoms join together, they make a molecule. A molecule is the smallest possible unit of a substance. For example, one water molecule is the smallest unit of water. (The water molecule is made up of three atoms –two hydrogen atoms and one oxygen atom.)
The word particle can refer to both atoms and molecules, but we generally use it to refer to the smallest possible piece of something. So, a water particle is just another way of describing a water molecule.
The vibrations travel through the air as waves of energy that reach our ears, and we hear these waves as sound. The substance that the sound-waves travel through is called the medium, and it could be a gas (like air) or a solid (like a table) or a liquid (like the sea). Once the waves run out of energy, we can’t hear them any more.
THE SHAPE OF A SOUND-WAVE
Sound-waves are longitudinal waves. This means that all the particles in the medium vibrate in the same direction as the movement of the wave. It’s helpful to think of this movement like a Slinky going down the stairs. The Slinky moves by stretching apart, then squashing together, with each coil pulling the one behind it forwards. In a sound-wave, the particles act like the coils in the Slinky. The scientific word for this stretching is rarefaction, and the squashing is compression.
Amplitude is a measure of the height of a wave. The greater the amplitude, or the stronger the vibration, the louder the sound. For example, if you’re playing a guitar and pluck a string hard, it will vibrate harder and make a louder sound than a string plucked gently.
If you are really far away from the object making the vibration, the sound becomes fainter by the time the vibrations reach you, because the soundwave loses energy and vibrates less the further it travels.
Wavelength is the distance between the highest point of each wave, and frequency is how many waves fit into one second. The shorter the wavelength, the higher the frequency. The longer the wavelength, the lower the frequency. At higher frequencies, the particles in the medium (such as the air) vibrate very quickly, and this creates a high-pitched noise. An example of a highfrequency sound is a mouse’s squeak. Meanwhile, low-frequency waves vibrate more slowly, and therefore create low-pitched noises, such as thunder.
AMPLITUDE
WAVELENGTH
SOUNDS IN DIFFERENT MEDIUMS
Density is a way of describing how many particles (or molecules) there are in a given area. If you fill a bottle with water, it will contain hundreds more particles of water than it did air when it was empty. This is because the water particles are packed closer together than the air particles so the water bottle is denser.
Do sounds move slower or faster when they travel through water? You might think the water would slow the vibrations down . . . but, actually, the opposite is true!
In a solid, the particles are very tightly packed and fixed in place.
In a liquid, the particles are closer together and can still move around, but not as easily.
In a gas, such as the air, the particles are very loosely packed and can move around freely.
Sound travels faster in a solid than in a liquid or in the air. This is because the particles in a solid are packed really tightly, so they can bump into each other more easily and the vibrations travel more quickly.
Sound travels faster in liquids than in air because the particles are closer together.
The speed of sound in air is faster in the summer than it is in the winter, because temperature affects the speed of sound. The warmer it is, the faster the particles can vibrate.
Since sound needs particles to vibrate, if there are no particles, there can be no sound. This means that in a vacuum (a place with no particles in it – not even air) sound can’t travel. Outer space is a vacuum, so in outer space sound can’t travel!
ECHO
. . . ECHO . . . ECHO . . .
Sound-waves can be reflected, refracted and diffracted.
A sound-wave is reflected when it bounces off a surface and travels back to your ears, and you can hear the sound as an echo.
Sound can also be refracted, or bent, when it travels from one medium to another, for example, from a liquid to a solid.
If sound is travelling and meets an obstacle, such as a tree or the corner of a room, it can be diffracted, or spread out and change direction.
