Sound

• Ultrasound- over 20,000 Hz
• Infrasound- under 20Hz
• Between what frequencies can humans hear?

  Most humans can hear frequencies between 20Hz and 20000Hz
• Ear canal: Channels the sound wave to the ear drum. This can get blocked by wax
• Ear drum: Sound wave in the air make this vibrate. This part of the ear can be damaged by infections
• Ossicles: These 3 bones pass on the vibrations from the ear drum. These parts can fuse together as you get older(otosclerosis)
• Cochlea: Tiny hairs that convert the vibrations into electrical impulses. This can be damaged by accidents or sudden loud noises.
• Auditory nerve: The electrical impulses travel along this to the brain. This part can be damaged by constant loud noises
• Echolocation template:

  1. Send out sound wave
  2. Sound reflects off object
  3. Measure time taken and half it
  4. Speed of sound in medium known
  5. Use formula d=st
  6. Use distances to build up a picture
• Wave transfers energy without moving the matter
• Sound is a longitudinal wave
• Sound is caused by the vibration of particles
• Sound travels faster the closer the particles
• Can we hear sound in vaccums?

  No as there are no particles for the vibrations to collide with
• Dolphin emits ultrasound which reflects off of a fish. By measuring the time it takes for the sound to reach the fish, we can work out how far away the fish is; use the formula d=st
• Compressions are followed by rarefractions
• In solids, the molecules are held close together so they vibrate more easily than those in liquids or gases. This means that sound waves travel much faster through solids than through liquids or gases.
• When an object vibrates, it causes nearby air particles to move back and forth. These moving particles then cause neighbouring particles to vibrate, creating a chain reaction. As this wave moves further from its source, the amplitude decreases until eventually the energy dissipates into heat.
• A longitudinal wave has compressions and rarefactions running parallel to the direction of propagation (the direction the wave is travelling).
• Frequency= number of waves/time

  f=n/t
• Frequency= 1/period

  f=1/T
• Pitch - the frequency of a sound wave
• Loudness - a measure of the amplitude of a wave trough
• Transverse waves travel perpendicular to its energy transfer
• Wavelength: The distance between two adjacent points on the same place on a wave. Eg. from peak to peak
• The speed equation can be used for waves:

  wave speed= distance/time

  s=d/t
• Wave speed= frequency x wavelength

  v=fλ
• wave speed (m/s)=v
• frequency(Hz)= f
• wavelength(m) = λ
• Frequency: the number of points past a given point per second
• Crest- highest point of a wave
• What direction does a longitudinal wave travel?

  Parallel to its energy transfer

  
• What direction do transfers waves travel in?

  Perpendicular to its energy transfer

  
• Amplitude: maximum displacement of a wave from its equilibrium position (the middle line)
• The outer ear is also known as the external ear