Learning object naysilla dayanara
Preview:
Citation preview
- 1. Sound Waves Learning Object (LO4) Naysilla Dayanara Section
L2H
- 2. Longitudinal Waves Waves in which the displacement of the
medium is in the same direction, or opposite to, the direction of
travel.
- 3. Medium The molecules of the medium oscillate as sound wave
passes through Stretched = Rarefraction PRESSURE IS LOWERED
Compressed=Compression PRESSUREISELEVATED
- 4. Different Ways to Describe Sound Wave P vs. position (x)
Displacement (y) vs. Position (x)
- 5. How much mass is oscillating Stiffness in 2D How much the
length of the string changes when we exert a force on it Speed of
Sound Recall textbook Sec 14-4 (p. 388) on Wave speed on a String
Depends on INERTIAL & ELASTIC properties of the medium Linear
mass density () Tension of String which gives us the equation:
Stiffness in 3D waves Measure by what fraction the volume changes
when we change the pressure exerted on the material
- 6. Speed of Sound The 3D equivalent of Stiffness is called the
Bulk Modulus Ratio of (P) and fractional change in volume (V/V)
Negative (-) sign: because V/V is always opposite of the sign of P
Similar to this equation How much mass is oscillating Density of
medium, how individual particle oscillates.
- 7. Displacement, Pressure, Intensity At High pressure:
Particles are pushed into it from left and right. Hence, at Pmax,
displacement must be 0 Left Side (+) displacement Right Side (-)
displacement Positive Negative Similarly, at Pmin, displacement is
also 0
- 8. Amplitude of pressure variation Comparing equations for P
and s(x,t), we see that although the wave function has a cosine
function and the pressure is a sine function, the arguments are the
same in both cases. They have the same wavelength, period, and wave
speed but are /2 out of phase (between sin and cos) This
relationship is plotted in the next slide.
- 9. Comparison
- 10. Displacement, Pressure, Intensity We now examine the energy
that a sound wave delivers (INTENSITY): Power delivered per unit
area Where P is the rate at which the wave delivers energy, and A
is the area that the wave is impinging upon. As shown previously
(one dimension) For a sound wave, replace the (linear mass density)
with rho (mass density). This substitution gives a new unit of W/m2
(Power/area = I) Therefore