Sound Waves

- sound waves CANNOT travel through a vacuum (limited to vibrations in a medium)
- Rarefaction: a decrease in the density of something; "a sound wave causes periodic rarefactions in its medium" (6 BR2)

- "compressions & rarefactions"
- Adiabatic: any process that occurs WITHOUT heat transfer (ex: engine breaking) ( ΔT ≠ 0 but Q = 0)
- Isothermal Process: any process that occurs WITHOUT a change in temperature (ΔT = 0 but Q ≠ 0)

- the speed of sound in air at room temp. is about 340m/s!

- v_{sound in solid} > v_{sound in liquid} > v_{sound in gas}

- because solids have stronger forces between them (IMFs), thus greatest restoring force, thus can participate in another compression wave faster, thus can propogate SOUND faster in the medium (6 BR2)

β = 10 log₁₀ (I/I₀)

- Intensity (W/m²) – very LARGE number based on factors of 10, needs to be paired with a LOG expression

- Decible (β) – smaller, more reasonable number, because the answer to a log-based expression!

*** for every drop in intensity by a factor of 10, the decibel level decreases by 10:

- ex: if the intensity of a source increases by 1000 (3 factors of 10), then the decibel level of that sound will increase by 30 (3 x 10)

- ex2: if the intensity (I) increases by a factor of 10, then the intensity level (dB) increases by +10 dB. If the intensity increases by a factor of 100, then the intensity level increases by +20 dB. (USE THIS FOR ANSWER APPROXIMATION!!! Will probably be too complicated/time-wasting to sit and calculate actual logarithms!)

Intensity & Distance: the intensity of sound dissipates with distance by a SQUARED factor

ex: (Kaplan 371) Increasing distance by a factor of 10 decreases intensity by a factor of 100, therefore reducing the sound level by -20 dB.