physics sound and waves

wave

wave

disturbances that transfer energy over a distance

mechanical wave

wave that requires a medium in which to travel

medium

any material; solid, liquid, or gas

periodic motion

motion that occurs when the vibration, or oscillation, of an object is repeated in equal time intervals

pulse

wave that consists of a single disturbance

transverse vibration

occurs when an object vibrates perpendicular to its axis

longitudinal vibration

occurs when an object vibrates parallel to its axis

torsional vibration

occurs when an object twists around

cycle

one complete vibration or oscillation

rest position

position of the object before it moves or vibrates

amplitude

distance from the equilibrium (rest) position to maximum displacement

wavelength

distance between successive wave particles that are in phase

in phase (same phase)

points on a periodic wave that have the same frequency and same displacement (from rest position) and moving in the same direction

out of phase

points on a periodic wave that have the same frequency but not in phase

180 out of phase (opposite phase)

points on periodic wave that have the same frequency and opposite displacement (from rest position) and moving in the opposite direction

crest

high section of wave

trough

low section of wave

compression

region where the particles are closer together than normal

rarefaction

region where the particles are further apart than normal

audible sound wave

sound wave in the range of human hearing, 20Hz to 20kHz

infrasonic wave

sound wave with a frequency below 20Hz

ultrasonic wave

sound wave with a frequency above 20kHz

echo

the sound energy reflected off a surface back to the producer of the sound

Mach number (M)

the ratio of the airspeed of an object to the local speed of sound (airspeed/local speed)

Loudness

describes how humans perceive sound energy; dependent on sound intensity

pressure (p)

the force per unit area (F/A)

sound intensity

the amount of sound energy being transferred per unit area; unit W/m^2

decibel (dB)

the unit of sound level used to describe sound intensity level

constructive interference

occurs when waves build on each other to make a larger wave

destructive interference

occurs when waves diminish one another and create a smaller wave

standing wave

wave that is created when waves travelling in opposite directions have the same amplitude and wavelength

node

points that remain at rest

antinode

points midway between the nodes where maximum constructive interference occurs

supercrest

wave crest resulting from constructive interference

supertrough

wave trough resulting from constructive interference

first harmonic/ fundamental frequency

the simplest and lowest frequency standing wave

second harmonic/ first overtone

the second lowest frequency standing wave

third harmonic/ second overtone

the third lowest frequency standing wave

resonance

the increases in amplitude of a wave (or vibration) due to the transfer of energy in phase with the natural frequency of the wave

natural frequency (resonant frequency)

the frequency at which a medium vibrates most easily

sympathetic vibration

the resonance of a mechanical or acoustical system at its resonant frequency by energy transferred from an adjacent system vibrating at this same frequency

aeroelastic flutter

a wind induced vibration where the energy input from the wind equal or exceeds the energy lost due to damping, causing large (and potentially destructive) vibration

acoustical resonance

resonance involving sound wave

beats

periodic changes in sound intensity caused by interference between two nearly identical sound waves

echolocation

the process of determining the location of objects through the analysis of echoes, or reflected sound

pinna

• funnel for sound

• channels sound waves into the auditory canal

auditory canal

• part of the external ear

• magnifies sounds in the frequency range of 1000Hz to 5500Hz by a factor of about 10

tympanic membrane

• eardrum

• separates the outer ear from the middle ear

• tightly stretched, cone shaped membrane

• extremely sensitive

Eustachian tube

• connects the cavity containing the middle ear to the mouth

• filled with air

• only opens when you swallow or yawn

hammer, anvil, stirrup

• transmits the vibrations of the eardrum to the inner ear while magnifying the pressure variations by a factor of about 22

• three smallest bones in the body

hammer/malleus

• the centre of the eardrum on the inner side is connected to it

• lever-like bone that rocks back and forth when the eardrum vibrates

anvil/incus

• connected to the hammer

• vibration of the hammer causes it to vibrate

stirrup/stapes

• transmits the eardrum vibrations to the start of the inner ear at the oval window

• when eardrum is pushed in by a compression wave, it pushes inward on the oval window

• when rarefaction is present in the outer ear and the eardrum is pushed outward, it pulls the oval window outward

cochlea

• snail-shaped organ approximately 3cm long

• divided into two sections by the basilar membrane

• vibrations at the oval window cause pressure wavs in the fluid that fills it

basilar membrane

• partition that divides the cochlea into two sections

• responds to different frequencies along its length

• when resonance is achieved, it will vibrate in one area which causes microscopic hairs in the area to vibrate

semicircular canals

• three hard, fluid-filled loops in the inner ear

• right angles to each other

• act like accelerometers that help maintain the body’s balance by transmitting signals to the brain

hearing aid

• worn behind the ear or in the auditory canal

• magnifies sound and directs it to the ear

• consists of a microphone and an amplifier

outer ear

consists of the pinna and auditory canal

middle ear

consists of the eardrum and three small bones: the hammer, the anvil, and the stirrup

inner ear

consists of the cochlea and auditory nerve

building acoustics

the total effect of sound produced in an enclosed or restricted space

reverberation time

the time required for the loudness of the sound to drop by 60dB or until the sound is inaudible

tsunami

an enormous sea wave or a series of enormous sea waves caused by an earthquake or other disturbance

seismic waves

waves of energy that travel through earth

buffet

a type of random vibration that is usually caused by an interruption of airflow