• Sounds are made as a result of vibrations or oscillations (things bouncing up and down!)
  • To change the pitch of sounds from musical instruments you make the string/pipe longer for lower pitched notes
  • Frequency of vibration relates to pitch of note - high frequency is high pitch and vice versa.
  • To change the loudness of sounds from musical instruments you pluck/blow the string/pipe harder for louder notes
  • Amplitude of vibration relates to loudness of note - large amplitude is loud note and vice versa.
  • You must use appropriate scientific language to describe features of a sound wave
  • Vibrations that make sound are transferred through a medium by particles of that medium vibrating and passing the vibrations to neighbouring partilces
  • Sound cannot travel through a vacuum (it needs particles to pass on the energy and a vacuum has no particles in it - it is empty space!)
  • To explain how sound travels you must relate sound travelling through a medium to the particle model
  • Sound travels at different speeds in different types of material
  • Using the particle model to explain how sound travels we can explain that sounds travels best through solids as the particles are closely packed - therefore sound travels fastest through solids, then liquids and slowest through gases and not at all through a vacuum!
  • How we hear:
    • The energy of sound is transferred through the eardrum to the middle ear.
    • Effects of vibration to the eardrum are transferred to the brain (the cochlea changes the mechanical vibrations into electrical signals and the auditory nerve sends the signals to the brain).
    • Different people can hear different ranges of pitch because hearing changes with age (frequency perception at high values decreases as you get older) but generally humans hear frequencies between 20 Hz and 20 kHz.
  • Some animals detect sounds that are inaudible to human ears - either infrasonic (belowe the human hearing range) or ultra sonic (above the human hearing range)
  • We can compare loudness  by either using the dB scale or looking at the change in amplitude on a graphical representation - or an oscilloscope trace.
  • Loud sounds can damage hearing - they can perforate the eardrum - long exposure to loud sound (using an ipod with the volume up too high) can permanently damage hearing - make your ears act 'older' than they should be!
  • Echo calculations: The reflection of sound is an echo. We can use how long it takes for an echo to 'bounce back' to us to work out distances. (See example on the cyberphysics sound page)

Videos to look at when revising : Sound

Definitions to learn by heart

Frequency

(f)

is the number of vibrations per second.

It is measured in

hertz (Hz)

Amplitude

(A)

is the maximum displacement from the mean position.

It is measured in

metres (m)

Wavelength

()

is the shortest distance between two corresponding points on a wave.

It is measured in

metres (m).

 

For a soundwave the wavelength is the shortest distance between two particles of 'the medium the sound is travelling in', that are oscillating in phase. (Shortest distance between two particles that are moving in step with each other)