Musical springs
Can you make music with an elastic band? Here is what to do. Take an elastic band and loop it round your thumb and first finger. Move your thumb and first finger apart. As they move apart you may feel the elastic band digging into your skin. It is now ready to be played. Use a finger of your other hand to grab hold of one side of the elastic band. Pull on this side until it is much tighter, then let it go. The elastic band shakes about so much that you cannot see it but you may hear a musical note. What has been going on?

An elastic band is made from an elastic plastic. This material can be stretched but the moment it is no longer stretched it springs back to its original shape. An elastic band just cannot move without a force acting on it. When you let go of a stretched elastic band you know that you are no longer pulling on it, so where is the force coming from? When a springy material is stretched a force is made inside it. This force is called a strain force. As you pull on the side of the elastic band a strain force forms inside the band. It matches the strength of your pull. When you let go of the elastic band there is no longer a force to match the strain force. It is on its own, so it pulls the elastic band back to its original length. In fact it does more than this: it makes the elastic band shake very fast. This movement is called vibrating. But how is this movement turned into sound that we can hear?

Around the elastic band is air. You may not think that there is anything in air but a simple experiment can show you that you are wrong. If you take two balloons and blow one up, then try and balance them on a see-saw made with a coat hanger you may be surprised at what you find. If air is nothing you would expect the two balloons to balance. What you find is that the balloon you have blown up weighs more than the empty balloon so air has some weight but what is it made of? Scientists have found that it is made of tiny particles that we cannot see. They move about freely. When an elastic band shakes or vibrates it makes the air particles around it vibrate too. They shake the air particles next to them and the shaking or vibrating is passed through the air to our ears. When the vibrating air reaches our ears it makes vibrations in our ears which we hear as sounds.

The first note you make with your elastic band may not have been tuneful but you can try again. Usually people do not stretch the elastic band very much at first and it makes a low note. When they try again, they move their finger and thumb further apart to make the elastic band stretch more. This time, when the elastic band is stretched it vibrates more quickly and this makes a higher sounding note.

Take an elastic band and have a go at stretching it to different lengths then plucking it. You should find that you can make high notes and low notes. Perhaps you can work out a way of stretching the elastic bands to different lengths to make a tune.

Do all elastic bands make the same notes?
No. A thick elastic rubber band makes low notes. A thin elastic band makes higher notes.

How can you tell the difference between a high note and a low note?
When you sing the word "ping" you are making a high note. When you sing the word "pong" you are making a low note. Just try and sing them and you will find that your mouth and throat move to make them.

What makes the sounds of our voice?
Your voice is made by vibrations. They are produced by two elastic flaps in your throat. They are called your vocal cords. Your vocal cords are in your voice box. If you feel at the front of your neck you will find a hard part beneath your skin. This is your voice box. If you put your fingers on it and sing "Arh" loudly you will feel your voice box vibrate. These movements are started by the vocal cords. You speak or sing as you breathe out. As you release the air, it passes through your mouth and when you alter the shape of your mouth you alter the sound that comes out.

Can you make a musical instrument with elastic bands?
Yes. You need six elastic bands with different thicknesses. You then need to take a cardboard box and cut a large hole in one side. Finally stretch the elastic bands
round the box so that they pass over the hole. When you pluck the elastic bands you should find that you can make a range of musical notes.

Why do you need a hole in the box?
When the elastic band is plucked it vibrates and sets the air in the box vibrating too. This makes the box vibrate and the whole instrument makes a much louder sound than an elastic band vibrating on its own.

Can you make an elastic band make quiet sounds and loud sounds on your fingers?
Yes, you can. If you only stretch the elastic band a little, then let it go, only a small strain force forms inside it. This makes the band vibrate only a little so the air vibrates only a little and your ears vibrate only a little. The small vibration makes a quiet sound. If you stretch the elastic band greatly, then let it go, a large strain force forms inside it. This makes the elastic band vibrate much more strongly and the strong vibrations are passed through the air to the ear. We hear these string vibrations as loud sounds.

Are the strings on a guitar all alike?
No. Most guitars have six strings. The strings are arranged in order of thickness. The top string is the thickest and the bottom string is the thinnest. When the guitarist wants to play low notes he or she uses the top strings. When he or she wants to play high notes the guitarist uses the bottom strings.

Why do guitarists move their fingers across the strings?
They move their fingers to press down on the strings. When a string is pressed down the length that vibrates is made shorter. This makes the string play a higher note than normal. There are metal bars on the arm of the guitar called frets, which help guitarists place their fingers so they can make different notes with each string. If the guitarist did not press down on the strings only six notes ? one for each string ? could be made. By making the strings shorter a large number of notes can be made.

Do other musicians move their fingers to shorten strings?
Yes, they do. Just watch a person playing a violin, cello, double bass or banjo.

How does a pianist shorten the strings in a piano?
The piano contains a huge number of strings of different lengths so the pianist does not need to shorten any of them. He or she simply chooses the right string to play by pressing down the correct key on the keyboard.

How are piano strings plucked?
They are not plucked. Each key is connected to a felt-covered hammer. When the key is pressed down the hammer strikes the string and makes the string vibrate.

Are piano strings really made of string?
No. Although they are widely known as strings they are in fact made of springy wire called piano wire.

Do any musical instruments have springy sheets instead of strings and wires?
Yes, they do. Drums have a springy sheet called a drum skin. At one time they were made from animal skins but these days they are made from plastic. When the drum skin is beaten with a drumstick it vibrates and makes a sound.

Can a drum play different musical notes?
Yes, it can. The note that the drum plays depends on how much its skin is stretched. If the skin is stretched tightly it will make a high note. If the skin is not stretched tightly it will make a low note. Most drums are set or tuned to play one note but the kettle drum is different: it has a foot pedal which allows the drummer to change the stretchiness of the skin quickly and play a range of notes.