Sound

All sorts of things make sounds but all of them have one thing in common :- something is vibrating, moving backwards and forwards very very fast. So fast that it is not always easy to see what is moving. Even when you can see the movement it is so fast that it just looks like a bit of a blur.

Look carefully at the strings of a guitar when they are plucked and you can see what I mean. Sometimes it is easier to feel the vibration, try feeling your voice box as you talk or gently pinch the edge of a cymbal after it has been hit. Try putting rice onto a drum and then playing it or putting the end of a vibrating tuning fork into some water.

But how do these sounds get to our ears? They must travel through the air. When the guitar string vibrates it pushes the air beside it back and forth and this back and forth movement spreads out through the air. The vibration moves through the air until the air next to our ears is also moving. Then this air pushes back and forwards against our ear drums and we can hear the sound.

Sound can also travel through other materials as well as air. Put your head underwater in the bath or at the swimming pool and you will still hear sounds, although they might sound a little strange. Sound can even travel through walls- turn your stereo up full blast and see how long it takes your neighbours to notice! some materials can let sound pass easily (conductors) others tend to absorb the sound and stop it (insulators).

Sound can also go around obstacles. If you leave your window open it is easy to hear what is going on outside even when you can't see anything. Sound bounces back from some surfaces and you can hear an echo. Hard surfaces are good at bouncing back sound (for example the tiles at the swimming baths) soft materials tend not to make echoes.

The volume of a sound is how LOUD or quiet it is. When you hit the drum really hard you make it vibrate alot, this makes a loud sound.
The pitch of a sound is how high or low it is. This is the speed of the vibration, the faster something vibrates the higher the note - the slower it vibrates the lower the note.
A large fast vibration will make a loud high note, but a small slow vibration will make a quiet low note. If you have the Flash 5 plug in you can try this out below !

Big drums normally vibrate slower than small drums so they make lower notes. You can sometimes make drum skins vibrate faster by stretching the skins tighter, this makes them play a higher note.

The same is true of strings. A long string vibrates slower than a short string (thats why a double bass is so big). So you can change the pitch of a string by making it shorter or longer. It is also possible to change the pitch of a string by stretching it harder, the more you stretch it the faster it vibrates and the higher the note. If you look carefully at a guitar or iside a piano you might notice that the low notes are made by thicker strings than the high notes. The heavy thick strings are slow to move back and forwards so they make low notes. You can almost see them vibrating, but the thin strings are much lighter and easier to move so they vibrate faster and make high notes.

Can you plan your own investigation ?
Think about what you will try and test?
What will you need?
What will you need to do?
What are the things you will change? What will you try to keep the same?
How will you make sure your tests are 'fair'?
What are you going to measure or observe?
How will you present your results?