Science Year 9

• Medium


  The matter or substance through which sound is transmitted
• Types of medium

  • Solid
  • Liquid
  • Gas
• Air is the most common medium for sound propagation
• Sound cannot travel through a vacuum
• Sound is a mechanical wave that requires a medium to propagate
• In a vacuum, where there is an absence of matter, there is no medium for sound waves to travel through
• All sounds come from sources which vibrate
• Ampitude

  A way to describe how quiet or loud a sound appears
• Loudness

  • Depends on the distance of each vibration
  • Depends on how far away the vibrating object is
• Larger vibration


  Creates more energy, which is then transferred to the surrounding air molecules
• More vigorous bumping of air molecules

  Creates more intense sound waves that our ears perceive as louder
• Sounds get quieter when the distance from the vibrating object increases because of energy dissipation
• Energy dissipation

  Energy is transformed from one form to another and eventually dispersed or lost as it interacts with its surroundings
• When a sound wave travels forward in air, the particles move forward and backward
• Molecules of the air do not travel all the way from the loudspeaker to your ear
• You hear the sound because the vibrations are passed along from one molecule to the next
• Amplitude

  • The distance from zero to the top, or peak, of the graph
  • The distance from zero to the bottom, or trough, of the graph
• As the amplitude of a sound wave increases

  The loudness of the sound increases
• Oscilloscope


  A piece of equipment that displays waveforms of sound waves
• High-pitched sounds


  Have a high frequency, meaning they vibrate rapidly
• Low-pitched sounds

  Have a low frequency, meaning they vibrate more slowly
• The faster the vibrations, the higher the pitch of the sound
• Frequency

  The number of vibrations per second
• As the frequency of a sound wave increases

  The pitch of the sound also increases
• Unit of sound

  Hertz or Hz
• A frequency of 500 Hz means that 500 complete vibrations happen every second
• If the amplitudes are the same, the loudness of both these sounds are the same
• Interference

  The effect that is produced when sound waves meet each other
• Sound waves produce interference when they meet each other
• Interference can only happen when the waves are of the same type, sound waves cannot interfere with water waves
• Interference only happens when the waves have the same frequency and amplitude
• Interference can produce two effects

  • The waves can reinforce each other
  • The waves can cancel each other
• Reinforce


  To make stronger
• Waves will reinforce when they meet with the peaks together and with the troughs together
• The amplitudes of the two waves that interfere are added together
• The frequency of the two waves that interfere does not change
• When sound waves interfere to reinforce

  The amplitude increases
• Loudness of a sound wave

  Depends on its amplitude
• Two sound waves reinforce

  Amplitude increases, therefore the sound becomes louder
• Sound waves can meet and reinforce where there are two sources of the same sound