The Nature of Sound I Flashcards
what 3 things are related to mechanical vibrations
sound generation
propagation
perception of sound
particle motion
motion of the particles interacts with the particles near them, and the energy is transferred to them spreading out to more remote areas
what are sound waves
areas of pressure disturbances in the air
what does the propagation of sound rely on
presence of a medium
energy transfer takes time. what is this displacement
velocity
what is speed of sound and what does it depend on?
speed at which sound waves travel
medium in which sound travels
what type of wave is sound
mechanical
- transverse
- longitudinal
what is a transverse wave?
the movement of the particles of the medium is perpendicular to the motion of the source
what is a longitudinal wave?
the movement of the particles of the medium is in the same direction as the movement of the source
what is wavelength (λ)?
distance between the particles of the medium that represent two successive peaks or valleys
λ for transverse waves
distance from one peak to another or from one trough to another
λ for longitudinal waves
distance from one point of compression to the next point of equal compression or one point of rarefaction to the next point of equal rarefaction
wavelength equation
λ= velocity/frequency
amplitude
maximum displacement of the particles of the medium from the average resting position
amplitude in transverse waves
amplitude is reported in the direction that is perpendicular to wave source
- difference between the peak value and average value
amplitude in longitudinal waves
amplitude is reported in the direction of wave source
- difference between the density of the compressions and the average value of the compressions
frequency (f)
number of vibrations that occur in one second
- same for both wave types
Period (T)
time taken for one complete vibration
- same for both wave types
relationship between frequency and period
inverse
f=1/T
T=1/f
wave velocity
velocity at which the wave propagates
v= frequency x wavelength
effects of a medium
- usual experience is sound in air
- sound also can propagate in solids, fluids - sound CANNOT propagate in a vacuum (no media present)
characteristics of a medium
- as sound propagates is that there are local regions of increased, equal or decreased regions of compression
- amount of compression/rarefaction and the return to equilibrium that is possible depends on the medium (elasticity property)
elasticity
the ability of an object to return to equilibrium once it has been displaced from rest
what does the speed of propagation depend on
physical properties of the medium
speed of propagation in: pyrex, steel, water, air
Pyrex = 5640 m/sec
Steel = 4877 m/sec
Water = 1482 m/sec
Air = 343 m/sec
how does temperature affect speed
basic properties of the medium are altered by changes in temperature
density and speed for helium
Density (ρ) of air at normal temperature and pressure is 1.2kg/m3 in contrast to helium which has a density of 0.17 kg/m3
The speed of sound in helium is 927 m/s
to get sound, we need a source that what?
vibrates
young humans with normal hearing can hear vibrations that
range from 20 vibrations/sec (20 Hz) up to 20,000 vibrations/sec
(20,000 Hz). what does this assume?
- there is a medium for sound to propagate
- the amplitude of vibration is sufficient to allow hearing
Tuning forks
- designed to create a sound when struck
- size of the tuning fork a specific frequency is created.
- used to tune musical instruments
- can be used in clinical assessments
simple harmonic motion (SHM)
- described by a sine function
- sine wave
sine wave
a waveform that has periodic oscillations in which the amplitude of displacement at each point is proportional to the sine of the phase angle of the displacement
movement (pendulum)
- At 1, there is no movement
- The time it takes to go from 1 to 2 there is an acceleration
- The time it takes to go from 2 to 3 is less than the time to go from 1 to 2 so the acceleration is greater.
- At point 3 (center/middle) is the greatest acceleration
- From 3 to 4 the time it takes is less than the time from 4 to 5
- On the right side of 3 there is deceleration
- At 5 there is no movement briefly and changes direction
- The pattern in terms of acceleration and deceleration is now the same but in opposite directions
- SHM then is a consistent pattern of acceleration and
deceleration - The velocity is not constant
Restoring force
force that operates to bring medium back to a state of equilibrium
pendulum- gravity
tuning fork- springiness
Projected motion
image with constant distance between locations where each marking represents the output
ultrasound
above limits of human frequency
intrasound
below limits of human frequency
supersonic
speed greater than speed of propagation
sub-sonic
speed less than/below speed of propagation
Mach 1
speed of propagation of sound in air
