amplitude frequency and echoes

• Speed of sound


  The distance a sound travels divided by the time it takes
• Measuring speed of sound in air

  1. Distance

  2. Time
• Speed of sound in different materials

  • Gases slower than liquids, liquids slower than solids
  • No particles (vacuum) means no sound
• Speed of sound in different materials

  • Air (gas): 340 m/s
  • Water (liquid): 1500 m/s
  • Wood (solid): 3900 m/s
  • Space (vacuum): Sound cannot travel
• Echo


  A sound you hear after a sound wave reflects off something
• Calculating speed of sound from echo

  1. Distance to reflecting surface

  2. Time for echo
• Echoes in rooms


  • Hard, smooth surfaces reflect sound
  • Soft surfaces absorb sound
  • Rooms with soft surfaces produce less echoes
• Eardrum


  A thin flap of skin that is stretched tight like a drum
• Ear bones


  Three small bones called the hammer, anvil and stirrup
• Cochlea


  A spiral shaped part of the ear that looks a bit like a snail shell
• Auditory nerve


  The nerve that carries signals from the cochlea to the brain
• Pinna


  The visible portion of the outer ear
• How we hear


  1. Sound waves vibrate air particles in the ear canal

  2. Vibrations hit the eardrum

  3. Vibrations passed to the three ear bones

  4. Stirrup bone hits the cochlea

  5. Cochlea turns vibrations into electrical signals

  6. Signals sent to brain via auditory nerve

  7. Brain translates signals into the sound we hear
• Pitch


  How high or low a sound is
• Frequency


  The number of vibrations of the wave in one second, measured in hertz (Hz)
• Ultrasound


  Sound waves with a frequency higher than 20,000 Hz that humans cannot hear
• Animals that can hear ultrasound

  • Dogs (up to 60 kHz)
  • Bats (up to 200 kHz)
• A dog training whistle makes sound waves at 40,000 Hz, which dogs can hear but humans cannot
• Mosquito alarm


  A device that makes a noise at 17.4 kHz, which younger people can hear but older people cannot
• Sound travels faster through solids than liquids, which travel faster than gases.
• In general, sound travels fastest through solids (about 12 km/sec), slower through liquids (about 4 km/sec), and slowest through gases (about 300 m/sec).
• The speed of sound is the distance traveled by sound waves per unit time.
• Speed = Distance / Time