# Sound waves

#### elabed haidar

i have a question about sound waves :
we know that the equation of sound wave can be written in the form s=Sm cos(kx-wt)
,but i still dont get the meaning of Sm .I know that in the transverse wave ingeneral , and in particular the string the maximum amplitude is how much the string can go vertically upward ,
so what about the maximum amplitude in sound wave?
PS the defintion of sound wave amplitude is the maximum postion of the element at equilibrium ???

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#### tiny-tim

Homework Helper
hi elabed haidar!

as you know, s is displacement and sm is maximum displacement …

the displacement here is the distance any particular particle goes from its own equilibrium position …

in a transverse wave it goes up or down, and in a spring (or sound wave) it goes forward and backward
PS the defintion of sound wave amplitude is the maximum postion of the element at equilibrium ???
you mean the maximum postion of the element from its equilibrium position?

yes, the maximum distance forward or backward

#### elabed haidar

here is the problem i understand it in a spring Xm but in a sound wave i still dont get it

#### elabed haidar

one more thing in sound wave resonance why when we have tube which is one open from only one side the resonant frequency f=nv/4 lamda ?? and thank you very much professor

#### tiny-tim

Homework Helper
for pictures, google "longitudinal wave" and click "Images"

#### seonshrestha

why does longitudinal waves can propagate through solid, liquid and gas? and not transverse except in solid?

#### chrisbaird

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#### Trevormbarker

one more thing in sound wave resonance why when we have tube which is one open from only one side the resonant frequency f=nv/4 lamda ?? and thank you very much professor
Because the open end will have an antinode at it and you cant just have any wavelength because antinodes occur periodically

#### seonshrestha

Sound waves are pressure waves, so the picture of a longitudinal wave going down a spring is not always helpful. The amplitude of the sound wave is the maximum local air pressure reached when the wave traverses through it. So a sound wave with a higher amplitude (a louder sound) will have higher pressure. http://www.dailymotion.com/video/x6bz5x_plane-breaks-sound-barrier-then-exp_tech"
but how does mechanical longitudinal wave travel in solid, liquid and gas medium? and transverse mechanical wave (such as in rope)travels only in solid medium?

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