String instruments
Have you had some visiting musicians in your assembly? Perhaps they entertained you for half an hour or more. They encouraged you to sing along to their tunes or perhaps you were even allowed to play an instrument with them.

Imagine that your school is visited by a band of three musicians. One plays the piano, another plays a guitar and a third plays the violin. As they go through their performance let's have a look at how the instruments make their sounds. The music begins with the piano player. Her hands spread out over the keyboard and press down some keys. What happens when a piano key is pressed down? The key is connected to a number of levers. When it is pressed down the movement passes through the levers and makes a hammer swing towards a tightly stretched piece of wire. A fraction of a second later, the hammer strikes the wire and the wire vibrates. This sets off vibrations inside the piano and makes the piano sound a note. As the piano player continues, she presses down three keys at once and sets off three wires vibrating. These set off more vibrations in the piano and the three notes are heard together. A group of notes played together is called a chord. During this opening tune the piano player plays a mixture of single notes and chords and right at the end she plays a chord with both hands setting eight wires vibrating and sending out a loud sound to the back of the hall.

After the applause dies down, the guitar player starts the second tune. He only plays two notes, then stops and asks the piano player to help him tune his instrument. She plays a note on the piano and he plays the same one on one of the strings on his guitar. The strings run across the body of the guitar and up a wooden arm, which has six screws on its end. These screws are used for controlling the tension in the strings. When the guitar player plucks the string to play the note, he listens to the sound it makes and compares it with the sound coming from the piano. He turns the screw and tightens the string, then plucks it again and asks the piano player to play the same note again. This time he finds that both instruments play the same note perfectly. "That's good. They are both in tune now," he says and begins the second tune again.

As you watch the guitar player, you see that the strings on the guitar are not all the same thickness. The thickest string is at the top and the thinnest string is at the bottom. You also notice that he plucks the thicker string only occasionally and its deep sound seems to give a beat to the rest of the tune. He plucks the thinner strings, which make higher-pitched notes, to make the melody of the tune.

The wooden arm of the guitar has lines across it all the way from the body up to the tuning screws. This part of the guitar is called the fret board. As you watch the guitarist, you see his fingers press down some of the strings. This makes the length of the vibrating string shorter than it was before. The note made by the vibrating shorter string is higher pitched than when the string is allowed to vibrate along its full length.

During the tune, the guitar player plucks individual strings then sometimes rubs his thumb across several strings at once to make a chord. All the time, the fingers of his left hand go up and down the fret board shortening strings and then letting them go as notes of different pitch are played. Finally the tune comes to an end and the guitarist takes a bow. It is time for you to turn your attention to the violin player.

The guitar player had strung his guitar around his neck and rested it on his knee as he sat on a high stool. The violin player plays her instrument in a different way. She stands up and places one end of the violin body under her chin. She holds the other end of the instrument - the wooden arm that carries the strings to tightening pegs - with her left hand. Just before the third tune is about to start, the violin player takes the violin from her chin and puts it on a chair. She picks up a lump of dark-coloured substance and rubs it on the bow. This substance is called rosin and is used to help the bow slide quickly over the strings to make them vibrate. When the bowstring has been coated with rosin, the violinist picks up her violin, makes it comfortable under her chin and begins to play.

You notice that there are no frets on the wooden arm of the violin but the violinist still presses her fingers down on the strings to change their vibrating lengths. She seems to feel where her fingers should be to make the notes she needs. The part of the violin where the fingers are pressed down on the string is called the fingerboard. As the tune progresses her fingers dance up and down the fingerboard and the bow slides to and fro across the strings to make them vibrate.

The musicians' performance is over with the ending of the last tune but you can continue observing musicians playing stringed instruments. Have a look at video programmes of performing guitarists and violin players. Perhaps you could ask someone to let you have a go on a guitar. It will help you understand how strings can be used to make music.

How many keys are there on a piano?
Eighty eight and each one has a separate hammer and hits a separate wire. It may help you to think of a piano as eighty eight separate instruments.

How does a piano player change the length of the strings?
A piano does not have strings. It has wires but they behave exactly like strings.
A piano player does not change the length of the wires. All the wires are slightly different lengths to give the range of notes the piano can play. When a short wire is struck, it vibrates and makes a high-pitched note. When a long wire is struck, it vibrates and makes a low-pitched note.

What do the pedals on a piano do?
One pedal damps the sound of the strings and the other makes the notes echo. They do not alter the length of the strings.

If a guitar and a piano play the same note why don't they sound exactly alike?
When a note is played on the piano, the wire vibrates and sets the air inside the piano vibrating. This in turn makes the whole of the instrument vibrate and make the note which passes through the air to our ears. When the same note is played on a guitar, the string vibrates and this sets the bridge, which holds the strings on the body, vibrating. The vibrations pass to the body itself and to the air inside the body. The vibrations of the whole instrument make the note that we hear. As the piano and guitar have different shapes and sizes and are made from different materials they vibrate differently and give a particular sound to the note.

If different instruments sound different, how can you be sure that they are playing the same notes?
They play the same notes when they vibrate at the same rate. A tuning fork vibrates at a certain rate or frequency. When the tuning fork is struck, any instrument can be played at the same time and the sound of its note compared with that of the tuning fork. If the two notes have the same pitch, the instruments that are making them are vibrating at the same frequency and are playing the same note. If one note has a high pitch and the other a slightly lower one, the instruments are not vibrating at the same frequency and are not playing the same note. Most instruments can be modified in some way, such as altering the tension in the string of a guitar, to make them in tune with the other instruments that are being played.