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# Classification of Sound

In physics, sound is a vibration that propagates as a typically audible mechanical wave of pressure and displacement, through a medium such as air or water. In physiology andpsychology, sound is the reception of such waves and their perception by the brain

Sound is a longitudinal, mechanical wave.

Sound can travel through any medium, but it cannot travel through a vacuum. There is no sound in outer space.

Sound is a variation in pressure. A region of increased pressure on a sound wave is called acompression (or condensation). A region of decreased pressure on a sound wave is called ararefaction (or dilation).

The sources of sound

• vibrating solids
• rapid expansion or compression (explosions and implositons)
• Smooth (laminar) air flow around blunt obstacles may result in the formation of vorticies (the plural of vortex) that snap off or shed with a characteristic frequency. This process is called vortex shedding and is another means by which sound waves are formed. This is how a whistle or flute produces sound. Aslo the aeolian harp effect of singing power lines and fluttering venetian blinds.

What are the different characteristics of a wave? What are the things that can be measured about waves? Amplitude, frequency (and period), wavelength, speed, and maybe phase. Deal with each one in that order.

### Amplitude, Intensity, Loudness, Volume

Amplitude goes with intensity, loudness, or volume. That’s the basic idea. The details go in a separate section.

speed of sound

The speed of sound depends upon the type of medium and its state. It is generally affected by two things: elasticity and inertia.

solids

 v = √ K = √ γP = √ γkT ρ ρ M
 K = bulk modulus ρ = density γ = cP/cV (specific heat ratio) P = absolute pressure k = boltzmann’s constant T = absolute temperature M = molecular mass

solids

 v = √ E ρ
 E = young’s modulus ρ = density

liquids

 v = √ K ρ
 K = bulk modulus ρ = density