What What is is SOUND?SOUND? Sound is longitudinal pressure waves that travel through elastic media.

We can produce these vibrations by : Making a column of air vibrate, plucking a string, or by hitting an object

Sound Waves are caused by a source vibrating to and fro and causing successive compressions (squashing) and rarefactions (spreading out) in the medium; hence sound cannot travel in a vacuum. Sound waves are received by the ear, and interpreted by the brain.

Sound can vary in pitch – how high or low a note is. It can also vary in volume – how loud or how soft the note is

An amplifier makes the sound louder. We talk about the amplitude of the wave, which tells us how much energy there is. The taller the wave the louder the sound because more energy has been put in

The loudness depends on how much energy the sound wave has. In an electric key board an amplifier makes the sound louder. A louder note has a bigger amplitude. (height)

Loudness is measured in decibels dB

These help to make sound louder so the amplitude or height of the wave would be higher. The wave has more energy

The pitch depends on how many vibrations there are. The more frequent the vibrations the higher the note. The fewer the vibrations the lower the note

The higher the note, the more waves per second so the waves are squashed together. The waves will have a short wave length.

The lower the note, the FEWER waves per second so the waves are spread out. The waves will have a longer wave length.

Different instruments produce different shaped wave traces. The extra wiggles are known as harmonics. These give the instrument its “colour”.

Most instruments usually produce many frequencies or harmonics at the same time. All the harmonics add together to make a complicated waveform.

Here are some synthesized wave traces each shape represents a different kind of sound.

On the next few slides you will find internet sites that you can visit by clicking on the web address

How Stuff Works article on CDs and CD players How tape recorders work Short BrainPop movie about CDs and DVDs How CDs work, with an animated diagram micro.magnet.fsu.edu/electromag/java/cd/ micro.magnet.fsu.edu/electromag/java/cd/ How CDs and CD players work index.htm index.htm How analogue and digital recording works The technology of vinyl records compared with CDs An animated look at how a speaker works micro.magnet.fsu.edu/electromag/java/speaker/ micro.magnet.fsu.edu/electromag/java/speaker/

Watch a movie about sound Take an underwater sound quiz Find out why sonic booms occur, with help from a speeding motorboat How bats use echolocation members.aol.com/obcbats/ecolocation.html members.aol.com/obcbats/ecolocation.html