1 physics of sound
1.1 longitudinal , transverse waves
1.2 sound wave properties , characteristics
1.3 speed of sound
physics of sound
experiment using 2 tuning forks oscillating @ same frequency. 1 of forks being hit rubberized mallet. although first tuning fork hasn t been hit, while other fork visibly excited due oscillation caused periodic change in pressure , density of air hitting other fork, creating acoustic resonance between forks. however, if place piece of metal on prong, see effect dampens, , excitations become less , less pronounced resonance isn t achieved effectively.
sound can propagate through medium such air, water , solids longitudinal waves , transverse wave in solids (see longitudinal , transverse waves, below). sound waves generated sound source, such vibrating diaphragm of stereo speaker. sound source creates vibrations in surrounding medium. source continues vibrate medium, vibrations propagate away source @ speed of sound, forming sound wave. @ fixed distance source, pressure, velocity, , displacement of medium vary in time. @ instant in time, pressure, velocity, , displacement vary in space. note particles of medium not travel sound wave. intuitively obvious solid, , same true liquids , gases (that is, vibrations of particles in gas or liquid transport vibrations, while average position of particles on time not change). during propagation, waves can reflected, refracted, or attenuated medium.
the behavior of sound propagation affected 3 things:
a complex relationship between density , pressure of medium. relationship, affected temperature, determines speed of sound within medium.
motion of medium itself. if medium moving, movement may increase or decrease absolute speed of sound wave depending on direction of movement. example, sound moving through wind have speed of propagation increased speed of wind if sound , wind moving in same direction. if sound , wind moving in opposite directions, speed of sound wave decreased speed of wind.
the viscosity of medium. medium viscosity determines rate @ sound attenuated. many media, such air or water, attenuation due viscosity negligible.
when sound moving through medium not have constant physical properties, may refracted (either dispersed or focused).
spherical compression (longitudinal) waves
the mechanical vibrations can interpreted sound can travel through forms of matter: gases, liquids, solids, , plasmas. matter supports sound called medium. sound cannot travel through vacuum.
longitudinal , transverse waves
sound transmitted through gases, plasma, , liquids longitudinal waves, called compression waves. requires medium propagate. through solids, however, can transmitted both longitudinal waves , transverse waves. longitudinal sound waves waves of alternating pressure deviations equilibrium pressure, causing local regions of compression , rarefaction, while transverse waves (in solids) waves of alternating shear stress @ right angle direction of propagation.
sound waves may viewed using parabolic mirrors , objects produce sound.
the energy carried oscillating sound wave converts , forth between potential energy of compression (in case of longitudinal waves) or lateral displacement strain (in case of transverse waves) of matter, , kinetic energy of displacement velocity of particles of medium.
sound wave properties , characteristics
a pressure on time graph of 20 ms recording of clarinet tone demonstrates 2 fundamental elements of sound: pressure , time.
sounds can represented mixture of component sinusoidal waves of different frequencies. bottom waves have higher frequencies above. horizontal axis represents time.
although there many complexities relating transmission of sounds, @ point of reception (i.e. ears), sound readily dividable 2 simple elements: pressure , time. these fundamental elements form basis of sound waves. can used describe, in absolute terms, every sound hear.
however, in order understand sound more fully, complex wave such separated component parts, combination of various sound wave frequencies (and noise).
sound waves simplified description in terms of sinusoidal plane waves, characterized these generic properties:
frequency, or inverse, wavelength
amplitude, sound pressure or intensity
speed of sound
direction
sound perceptible humans has frequencies 20 hz 20,000 hz. in air @ standard temperature , pressure, corresponding wavelengths of sound waves range 17 m 17 mm. speed , direction combined velocity vector; wave number , direction combined wave vector.
transverse waves, known shear waves, have additional property, polarization, , not characteristic of sound waves.
speed of sound
u.s. navy f/a-18 approaching speed of sound. white halo formed condensed water droplets thought result drop in air pressure around aircraft (see prandtl-glauert singularity).
the speed of sound depends on medium waves pass through, , fundamental property of material. first significant effort towards measurement of speed of sound made isaac newton. believed speed of sound in particular substance equal square root of pressure acting on divided density:
c
=
p
ρ
{\displaystyle c={\sqrt {p \over \rho }}\,}
this later proven wrong when found incorrectly derive speed. french mathematician laplace corrected formula deducing phenomenon of sound travelling not isothermal, believed newton, adiabatic. added factor equation—gamma—and multiplied
γ
{\displaystyle {\sqrt {\gamma }}\,}
p
ρ
{\displaystyle {\sqrt {p \over \rho }}\,}
, coming equation
c
=
γ
⋅
p
ρ
{\displaystyle c={\sqrt {\gamma \cdot {p \over \rho }}}\,}
. since
k
=
γ
⋅
p
{\displaystyle k=\gamma \cdot p\,}
, final equation came
c
=
k
ρ
{\displaystyle c={\sqrt {\frac {k}{\rho }}}\,}
, known newton-laplace equation. in equation, k = elastic bulk modulus, c = velocity of sound, ,
ρ
{\displaystyle {\rho }}
= density. thus, speed of sound proportional square root of ratio of bulk modulus of medium density.
those physical properties , speed of sound change ambient conditions. example, speed of sound in gases depends on temperature. in 20 °c (68 °f) air @ sea level, speed of sound approximately 343 m/s (1,230 km/h; 767 mph) using formula v = (331 + 0.6 t) m/s . in fresh water, @ 20 °c, speed of sound approximately 1,482 m/s (5,335 km/h; 3,315 mph). in steel, speed of sound 5,960 m/s (21,460 km/h; 13,330 mph). speed of sound sensitive, being subject second-order anharmonic effect, sound amplitude, means there non-linear propagation effects, such production of harmonics , mixed tones not present in original sound (see parametric array).
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