# Sound. Sound Waves travel as compressions & expansions Alternating regions of compressed and expanded air These regions move away from source as longitudinal.

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Sound

Sound Waves travel as compressions & expansions Alternating regions of compressed and expanded air These regions move away from source as longitudinal wave

Same for all frequencies Remember v=f λ …. And v only depends on medium, not f

Normal atmospheric pressure and temperature speed of sound is 343 m/s. Speed of sound is determined by properties of medium that it travels through Speed of sound increases with temperature More rigid/stiff an object is… the faster sound will travel through it Steel – 5960 m/s Plastic – 2680 m/s Fresh Water @ 20° C – 1482 m/s Air – 340 m/s

Use speed of sound to calculate how far lightning is away from you

The pitch of a sound is simply the frequency of the sound wave Higher frequency, higher the pitch Humans can typically hear pitches ranging from 20 Hz (infrasonic) to 20,000 Hz (ultrasonic), but that range diminishes as you age… typically at the high end Loudness of a sound is affected only by amplitude

Two tones of slightly different frequency are sounded together. This produces a fluctuation in the loudness of combined sounds. Amount of beats per second is equal to the difference in frequencies. F beat = |f 1 -f 2 | Two tuning forks…. One 340 Hz another 310 Hz are sounded together. Beats will occur at a frequency of 30 Hz

Guitar strings, flute Blowing air across the open end of a bottle In general a standing wave in a bottle has a node at bottom and antinode at the top

First Harmonic w node at bottom and antinode at top would be ¼ of a wavelength fitting in the bottle So λ= ¼ L and f 1 = v/4L In general,

Must have antinode at each open end

The frequency of a sound wave will change do to the perceived motion of the sound source Waves bunched when approaching (high F, low λ) Waves spread out when receding (low F, high λ)

Waves From an object that is approaching have short wavelength, which means they have a higher freq. And a higher pitch waves coming from an object that is moving away from you have a longer wavelength and therefore a lower freq, and lower pitch Cars approaching and leaving

Sometimes the source of a wave can travel faster than the waves it is creating http://www.youtube.com/watch?v=6o0zmafxTmE&safe =active http://www.youtube.com/watch?v=6o0zmafxTmE&safe =active Can be easily seen with a speed boat http://www.youtube.com/watch?v=2Sv4o4Kktm4&safe =active http://www.youtube.com/watch?v=2Sv4o4Kktm4&safe =active Sonic boom created when a object or plane breaks through the sound barrier

Loudness is determined by Intensity

Doubling loudness corresponds to increasing the intensity by a factor of 10. 2x as loud means a 10 dB increase in Intensity

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