Karakteristi k
Gelombang Bunyi
Pendidikan Fisika FKIP UNS
Need medium
• Temperature for gas
• Elastic and inelastic properties for the other
Different speed in different
material.
• Loudness is related to intensity
• Pitch is related to frequency
Loudness and pitch
Audible range
• 20 Hz – 20.000 Hz
Ultrasonic
• > 20.000 Hz
• Exp/: Dog (max 50.000 Hz), Bats (max 100.000), USG
Infrasonic
• <20 Hz
• Exp/: earthquakes, thunder
• Sound is vibration of the molecules of the medium in which it travels or motion or displacement of the
molecules
• Sometimes longitudinal waves are called pressure waves.
Problem
PERIODIC SOUND WAVES
• The darker parts of the colored areas in this figure represent regions where the gas is compressed and thus the density and pressure are above their
equilibrium values. A compressed region is formed whenever the piston is pushed into the tube.
• called a condensation
PERIODIC SOUND WAVES
• the gas in front of it expands, and the pressure and density in this region fall
below their equilibrium values (represented by the lighter parts of the colored areas)
• called rarefactions
• Both regions move with a speed equal to the speed of sound in the medium.
PERIODIC SOUND WAVES
• The distance between two successive condensations (or two successive rarefactions) equals the wavelength λ.
• As these regions travel through the tube, any small volume of the medium
moves with simple harmonic motion parallel to the direction of the wave. If s(x, t) is the displacement of a small volume element from its equilibrium position, we can express this harmonic displacement function
… 1
• smax is the maximum displacement of the medium from equilibrium
• k is the angular wavenumber
• Ѡ is the angular frequency of the piston
PERIODIC SOUND WAVES
• the variation in the gas pressure P,
measured from the equilibrium value, is also periodic and for the displacement function in Equation 1 is given by
… 2
• ΔPmax is the maximum change in pressure from the equilibrium value