Sound

Sound

1. How is sound produced?

   • Sounds are produced due to interactions between molecules of a medium caused by a vibrating source.
   • Sound produces vibration / vice versa
     • Singing bowl
       • When the bowl starts to "sing", droplets of water jump up and down. This is due to vibration.
     • Sound and Salt
       • The salt particles begin to vibrate after the sound is played. The higher the pitch, the more complicated the pattern.
     • Sound and Glass
       • The glass vibrates and shatters when a high-pitch sound is applied to it.
     • String instruments
       • When the guitar string is plucked, it vibrates and produces sound.
     • Tuning fork
       • When you hit the tuning fork, you can see a vibration on the tuning fork. A sound is produced and is heard when placed near the ear.

2. Travelling of sound

   • Energy passed to surrounding molecules
     • Pushing and pulling layers of molecules surrounding it
       • Layers of air form compression and rarefaction.
         • Compression
           • Air molecules are closer together
         • Rarefaction
           • Air molecules are further from each other
   • Vacuum
     • NO matter
       • Sound cannot be heard
         • No particles for the sound to be carried
   • Requires matter to surround the sound
     • Solid
       • Speed of sound: 6000 m/s
         • Highest because molecules are closer
           • Transmission of sound is faster
     • Liquid
       • 1500 m/s
     • Gas
       • 330 m/s

3. How we hear sound

   • Ear is a sensitive device which functions with hearing
   • Ear allows to convert audible frequencies into electrical signals
   • 3 parts: Outer              Middle             Inner Ear
   • Outer Ear / Pinna collects sound from the surroundings and passes through auditory canal to the ear drum
   • Eardrum: Thin membrane that vibrates when catches compression and rarefaction of sound.
   • Middle Ear : 3 bones Hammer Anvil and Stirrup
   • Vibrations of eardrum are amplified many times by ear bones and turned into electric signals by cochlea which are passed thru auditory nerve to brain. The brain interprets them as sound.

4. Uses

   • Healing wounds
   • Levitation
   • Echolocation / Flash sonar
   • Curing cancer
   • Cymatic Patterns

5. Pitch

   • Frequency
     • Hertz (Hz)
       • Human Hearing range : 20 Hz- 20000 Hz
     • Number of cycles (rarefactions) in a second
       • First find the number of cycles in the sound wave eg From A to B is 5 cycles
       • Then find out how many seconds it took for the sound to come from the start to the end. eg It took 2 seconds from A to B
       • Divide no. of cycles by seconds eg 5cycles/2s = 2.5Hz
   • Higher/Lower sounds

6. Loudness

   • larger vibration, louder sounds

7. Sound and Society

   • For Entertainment
   • Warning of danger
     • Police car
     • Ambulance
     • Snakes
   • Sonar
     • Sonar is an acronym for SOund Navigation And Ranging
     • It is a technique that uses sound to gather information about the environment ( use sound wave to collect data / measure distance )
     • http://www.youtube.com/watch?v=MzRk2EBYlxQ
   • Ultrasound
     • Sound with frequencies above human range
       • above 26,000 Hz
     • Reflected waves can be used to
       • Create images of foestuses in pregnant moms
       • detect cancers
       • Observe tumours

Images and files in the map