Unit 5 - Sound and Waves Flashcards
Sound
a form of energy that is transmitted as a longitudinal wave through a medium and which can stimulate the human ear
only the energy travels, each particle remains in the same region
Waves
transfer of energy in the form of a disturbance through a medium
exceptions = electromagnetic radiation, which is a disturbance in electric and magnetic fields)
Wave characteristics (cycle, wavelength, period, frequency, Hertz, amplitude)
cycle = complete sequence of motion that repeats itself wavelength = length in metres of one cycle period = time to complete one cycle and is measured in seconds frequency = number of cycles in a given time period, cycles per second Hertz = honours Heinrich Rudolf Hertz, a physicist, unit for frequency amplitude = maximum disturbance of a particle from its zero point, measured in metres
Speed of sound
in general, sound travels faster in solids and slowest in gases, due to the kinetic molecular theory
particles are closest together in solids, and particles move faster when temperature rises
Echolocation
echolocation = sounds that are used to locate objects, also referred to as sonar
dolphins emit high frequency pulses and clicks to locate objects
bats sonar abilities enable them to detect differences in objects that are very close, about 1 million times more sensitive than any radar device
birds emit lower frequency clicks and pulses, which are less effective, for navigation
Mach number
ratio of the speed of a body to the speed of sound in the surrounding medium
used to express the speed of objects that travel faster than the speed of sound
Types of speeds
supersonic = travelling at a speed greater than Mach 1 subsonic = travelling at a speed less than Mach 1 hypersonic = travelling at a speed greater than or equal to Mach 5
Sonic shock and acoustic pressure
sonic shock = the buildup of energy as a sound source approaches the speed of sound
acoustic pressure = the change in air pressure produced by sound waves
Sound barrier
used to describe the buildup of sound waves in front of an object as it nears the speed of sound
in order to break the sound barrier, the object must run faster than the sound waves that they are emitting, and break the pressure wall that has been created
when pilots tried to reach Mach 1, the steering mechanisms on the plane became locked due to the air pressure surrounding the plane
Pressure wakes
pressure wake of a plane is similar to the water wake of a boat
the pressure waves spread out and move down towards the ground in an ever expanding cone
there are two different waves, one from the nose (leading edge wave), and one from the wing tips (trailing edge wave)
Supersonic travel
supersonic travel is prohibited over North America, unless the plane is sufficiently high enough
this assures that the pressure waves die of well before the reach the ground
Sound intensity
the amplitude of a sound wave determines sound intensity (volume, loudness)
sound energy radiates outwards from the source
the energy is dispersed over an increasingly large sphere
humans have a range of hearing, on average, from 10-12 W/m2 to 1 W/m2
Decibels
decibels are an example of a logarithmic scale
a logarithm is a number expressed as 10 to an exponent
0 dB is the threshold of hearing for the average person, however some people can hear sounds quieter than this
The Doppler effect
the Doppler effect is the apparent change in frequency detected by a stationary observer when the source of the sound is moving
as a fast car moves forward, it catches up a bit to the forward-moving compressions while distancing itself from those moving backwards
when the next compression is produced, it is closer to the previous one than it would be if the car was stationary
Characteristics of sound (pitch, infrasound, ultrasound)
pitch = the pitch is determined by the frequency of the sound waves infrasound = frequency lower than the average person can hear (less than 20 Hz) ultrasound = frequency higher than the average newborn can hear (greater than 20 000 Hz)
Industrial uses of ultrasound
reflectoscope = device used to find flaws in materials such as tires and casings, sends out short bursts of ultrasound, and any flaws in the materials show up as variations emulsifiers = high-frequency sound waves can cause liquids that would not normally mix to emulsify, metal alloys can be made using this process humidifiers = ultrasound creates a fine mist from a storage unit of water, used to humidify the air
Medical uses of ultrasound
diagnostics = sound waves travel through the body and are reflected back by different organs, high-resolution detection systems can discern abnormalities surgery = ultrasound can be used to break up kidney stones so that they can be passed without great discomfort
The principle of superposition
interference occurs when two waves meet in the same place simultaneously
principle of superposition = the amplitude of a particle that’s affected by two waves simultaneously is the vector sum of the two different amplitudes
the waves don’t affect each other, just the medium
each wave maintains its original speed, amplitude, and direction
constructive interference = when two crests or two troughs meet
destructive interference = when a crest meets a trough
Hearing
ears are most sensitive to mid-range frequencies
tinnitus = constant ringing in the ears caused by illness, genetics, or permanent ear damage
there are tens of thousands of hair-like cells lining the cochlea which are sensitive to high frequencies and are extremely delicate
they can be ripped out by large noises and cannot grow back
Standing waves
a standing waves interference pattern may occur when a wave interferes with its reflection, or with an identical wave
node = points where particles remain at rest (destructive interference)
antinode = points where double crest and double troughs occur (constructive interference)
in a longitudinal wave, antinodes are locations of double rarefactions and double compressions
Resonance
every object has a natural frequency at which it will vibrate
resonance = the response of an object or a medium to a periodic force that has the same frequency as the object’s natural frequency
mechanical resonance = an object vibrates, eg. bridge, pendulum, skyscraper
acoustical resonance = air vibrates so that a sound is heard, this occurs when air in a container is the correct length to amplify a certain frequency
Resonance in a closed air column
on end of the air column is closed eg. bottle, speaker cabinet, violin
a node occurs at the closed end and an antinode occurs at the opening
a loud sound is heard at ¼ of a wavelength for the first resonant length, this is the fundamental frequency
loud sounds are heard every ½ of a wavelength beyond that
if a sound of many frequencies occurs at the opening, the frequency heard above all others will be the one for which the column length is ¼ of a wavelength
Resonance in an open air column
the column is open at both ends
an antinode occurs at each end
the fundamental frequency is ½ of a wavelength and loud sounds are heard every ½ of a wavelength beyond that
if a sound of many frequencies occurs at the opening, the frequency heard above all others will be the one for which the column length is ½ of a wavelength
Beats
these are caused by the interference of sound waves with slightly different frequencies and wavelengths
because the wavelengths are not equal and the compressions and rarefactions occurs at different times, at certain points constructive interference occurs, and other times destructive interference occurs
beat frequency is the number of loud sounds per second
in general, most people can’t distinguish more than about 7 beats/second
application = tuning musical instruments with tuning forks, when the beat frequency is 0, it is in tune
Variables of strings
length = frequency varies inversely as the length, if the length is halved the frequency doubles, frequency increases when the length decreases tension = frequency varies directly as the square root of the tension, if tension increases by a factor of 4 the frequency doubles diameter = frequency varies inversely as the diameter, if the diameter is halved, then the frequency doubles density = frequency varies inversely as the square root of the density, if the density is quartered than the frequency doubles
Music (pitch, loudness, quality, first harmonic, harmonics and overtones)
pitch = highness or lowness of a musical note, a higher pitch has a higher frequency
loudness = related to the amplitude of a sound wave, the greater the amplitude, the higher the volume of the sound
quality = the complexity of the waveform, degree of richness of a sound, the more harmonic frequencies, the richer the quality
first harmonic = the lowest frequency of a string, also called the fundamental frequency
harmonics and overtones = higher frequency of the string that are integer multiples of the fundamental frequency
The human ear (pinna, auditory canal, eardrum, eustachian tube, cochlea, semi-circular canals)
pinna = sound collector, directs sound from in front of us into our ears
auditory canal = sound is directed through the canal to the middle ear, the size is ideal for amplification in a certain range
eardrum - transmits the vibrations through three small bones, the hammer, the anvil, and then the stirrup
eustachian tube = connects middle ear to the throat, serves to equalize pressure
cochlea = contains a series of fine hairs that are activated by certain frequencies, they trigger nerve cells, sending a signal to the brain
semi-circular canals = filled with a fluid called endolymph, works in order to keep the body balanced
