There are three main types of musical instruments,and in each one the notes that can be produced depend on what is vibrating.
(a)blowing-all wind instruments work by a column of air vibrate.The pitch of the notes can be varied by changing the length of the air column.
(b)plucking strings-when the strings of a guitar are plucked they vibrate and the air around them starts to vibrate too.If you put your finger on the string you shorten the length of the bit that can vibrate,and this makes the pitch higher.Making strings tighter or using lighter strings also raises the pitch.
(c)tapping and hitting-drums make sound because of their covering vibrates,sending sound waves into the air.
Electric music--When the strings of an electric guitar or bass guitar are plucked,their vibrations are converted to electrical energy and then sent to an amplifier.Here the electrical signals are magnified and then sent to a loudspeaker where they are changed into sounds.
Synthesizers--Make music by using electric signals instead of vibrations.They are usually connected to a keyboard.Each note played on the keyboard sends a particular electric message to the synthesizer.This then sets up an electrical code for the sound that is wanted.The code is sent to an amplifier and then to a loudspesker,which converts it to sound.
Computer music--Several microcomputers have a tiny syntersizer inside the keyboard,which enable them to play simple tunes and make sounds.You have to type in a command such as 'sound' or 'ping' followed by the note you want and how long you want to play it.
Sounds that are loud,unwanted and unnecessary are described as noises.Noise is a form of pollution Busy places like school canteens,factories heavy traffic,are made up of a jumble of vibrations of different frequencies.Their vibrations are of a irregular pattern.The loudness of sounds and noises can be measured in decibels(dB).Very high decibel counts can damage people's ears and may cause deafness.Here are how loud some everyday sounds are.