Sound and Standing Waves

Basics of Sound Sound waves travel in longitudinal waves A crest of a sound wave is a compression, where the most particles exist A trough of a sound wave is a rarefaction, where the least particles exist

Sound Creation Sounds are made by vibrating an object This object vibrates at a specific frequency which produces a sound –Also known as pitch The loudness of a sound is based on the amplitude of the vibration (measured in decibels or dB)

Examples of Sound Waves 300Hz100Hz 400Hz80Hz 500Hz60Hz 800Hz40Hz

Resonance Occurs when an object is driven at its natural frequency At this frequency, the loudness or amplitude of the wave is increased greatly Example: a child on a swing story 27gwnnk4

Standing Waves A standing wave is a phenomena that occurs when the reflected wave and the incident wave interfere to create stationary nodes

Harmonics Each harmonic represents a standing wave that occurs when the object is driven at its natural frequency Tube examples…

Sound Interference Same as other wave interference –Crest + crest = increase amplitude –Crest + trough = decrease amplitude –Trough + trough = increase amplitude When the amplitude is increased, the sound gets louder

Sound Interference (cont.) Two sound waves add together to give a new wave If their frequencies are unequal, a new beat frequency is created

What interference and beats sound like… 400Hz and 401Hz 400Hz and 403Hz 400Hz and 405Hz 400Hz and 411Hz 400Hz and 450Hz

So we’re on the topic of human hearing… We can hear from 20 Hz to 20,000 Hz Depending on which study you look at, dogs can hear from about 50 Hz to about 50,000 or even 100,000 Hz –Dog whistles operate between kHz

How we hear? Sounds enter through the outer ear –The part we can see Then hits the eardrum This vibrates the bones which transmit the motion through fluid to the cocclea The cocclea has tiny hairs that then detect the motion and send the info to the brain When you swallow or yawn, this stretches muscles that replenish the air inside your ear

Other types of noise White noise –Sound with equal amplitude at all frequencies Pink Noise –Sound that, in essence, sounds like white noise to humans because of how we hear (lemme try and explain, but we’ll see how it goes) Brown Noise –Same as pink, only there is a decrease in power as there is an increase in frequency