2026-05-28 17:22

Status: #new

Tags: #physics #waves

Sound

Sound Velocity

Sound in different mediums

$V_{Solid}>V_{Liquid}>V_{Gas}$

Speed of sound in air:

$V_{Sound}=332+0.6T_c$ where temperature is in ${}^{\circ }$ Celsius

Mach number and Sonic speeds

• Mach number (M)
  • $\to M=\frac{\mathrm{speed}\mathrm{of}\mathrm{object}}{\mathrm{speed}\mathrm{of}\mathrm{sound}\mathrm{in}\mathrm{air}}=\frac{V_o}{V_{\mathrm{sound}}}$
• Subsonic - V < Speed of Sound $\to$ M < 1
• Supersonic - V > Speed of Sound $\to$ M > 1
• Hypersonic M $>5.0$

Sound Intensity and Level

Sound Intensity ($I$)

• The amount of sound energy hitting an area 1 $m^2$ in 1s ($\frac{w}{m^2}$)
• $I=\frac{P}{4\pi r^2}$, P = power, r is radius of object

Intensity Level (B)

• Measures Sound Intensity along a dB scale that is logarithmic
• $B=10\cdot \log (\frac{I_1}{I_0})$
• $I_1$ represents the sound intensity
• $I_0$ represents the threshold of hearing (CONSTANT)
  • $\to I_0=1.0\cdot {10}^{-12}\frac{w}{m^2}$

Loudness

• A completely subjective metric of perceived sound

Doppler effect

• $\to$ The apparent change in frequency as heard by an observer as a result of the relative motion of a source approaching an observer
• Velocity is conserved $\to$ $\lambda \uparrow f\downarrow$ and $\lambda \downarrow f\uparrow$

Full doppler reaction

• $f_{obs}=\frac{f_s(V\pm V_0)}{V\pm V_s}$
• V = speed of sound in air
• $f_s$ is the frequency of the source (Hz)
• $V+V_0$ observer moving towards the source $\to V-V_0$ observer moving away from the source
• $V+V_s$ source is moving away from the source $\to$ $V-V_s$ source moving towards the source

Diagram Explaining Doppler Effect and full doppler REACTION....

References