Waves: Part 2

Waves: Part 2

1. Sound

   • Sound is caused by mechanical vibrations in a substance, and travels as a wave
   • It can travel through liquids, solids and gases
   • Sound waves generally travel fastest in solids and slowest in gases
   • They cannot travel through a vacuum (like space) - can be tested by listening to a ringing bell in a 'bell jar'
   • As air is pumped out of the jar, the ringing sound fades away
   • Sound waves are longitudinal waves - The direction of the vibration is the same as the direction in which it travels
   • The range of frequencies that can be hears by the man ear is from 20Hz to 20,000Hz
   • The ability to hear high frequency sounds decreases with age

2. Sound continued...

   • Sound waves can be reflected to causes echoes
   • Only hard, flat surfaces such as flat walls and floors reflect sound
   • Soft things like carpets, curtains and furniture absorb sound
   • An empty room will sound different once carpets, curtains and furniture is put into it
   • Sound waves can be refracted
   • Refraction takes place at the boundaries between layers of air at different temperatures
   • Sound waves can also be diffracted

3. Musical Sounds

   • The pitch of a note depends on the frequency of the sound waves
     • Higher Frequency = Higher Pitch
   • The loudness of a sound depends on the amplitude of the sound waves
     • Greater Amplitude = Louder the sound
   • Differences in waveform can be shown on an oscillioscope
   • Tuning forks and signal generators produce 'pure' waveforms
   • Quality of a note depends on the waveform
   • Different instruments produce different waveforms, which is why they sound different from each other
   • Vibrations created in an instrument when it is played produce sound waves
   • In some instruments (e.g. a saxophone) a column of air vibrates
   • In others (e.g. a violin) strings vibrate
   • Some (e.g. xylophone) vibrate when they are struck