Sound

Sound is caused by mechanical vibrations in a substance, and travels as a wave. It can go through liquids, solids and gases. Sound waves generally travel fastest in solids and slowest in gases. They cannot travel thorugh a vaccum as they need particles. Sound waves are longtudinal. The direction of the vibrations is parallel to the direction that the wave is travelling in. The range of frequencies that can be heard by a human is from 20 hertz to 20,000 hertz. The ability to hear the higher frequency sounds deceases with age. 

Sound waves can be reflected to produce echoes:

• Only hard, flat surfaces reflect sound
• soft things absorb sounds

Sound waves can be refracted. Refraction takes place at the boundaries between layers of air at different temperatures.

Sound waves can also be diffracted.

• The pitch of a note depends on the frequency of the sound waves. The higher the frequency the higher the pitch.
• The loudness of a sound depends on the amplitude of the sound waves. the greater the amplitude the more enrgy the wave carries and the louder the sound.
• Differences in waveform can be shown on an oscilloscope.
• Turning forks and signal generators produce 'pure' waveforms.
• The quality of a note depends on the waveform.
• Different instruments produce different waveforms (why they sound different)
• Vibrations created in an instrument when it is played produce sound waves.