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We know that at least the waves inside a flute or laser make resonance waves,and simply we know that a standing wave is superposition of two waves that are propagating in oposit direction,for example Asin(kx-wt)+Asin(kx+wt)=2Asi(kx)cos(wt).which the result is telling you that the wave is not prapagating to any direction.i belive that these standing waves are not wave,becouse they are neither transverse nor longitudinal and they have no prpagation in any direction.another reason is that they are not satisfying in a general formulation of wave,it means f(x-vt).i want to understand is my conclusion right or not? And secondly if they are not propagating how we see the beam of laser,or how we hear the resonance of a flute? Are the waves that coming out of the cavity of laser or cavity of a flute standing waves? Or just inside them we have standing wave? if the outside wave of cavity is standing waves ,they are superposition of what two oposit propagating wave?and if no, the wave of outside cavity not a standing wave ,how is it possible that we hear the resonance of a flute even out of a cavity?

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closed as unclear what you're asking by CuriousOne, ACuriousMind, Gert, user36790, John Rennie Feb 3 '16 at 8:27

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  • $\begingroup$ As you said, a standing wave is the superposition of two waves propagating in opposite directions. I will leave it to the English department to declare whether the superposition of two waves propagating in opposite directions is a wave. It's certainly called that in physics. $\endgroup$ – CuriousOne Feb 1 '16 at 15:21
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The problem in answering this question is that the term wave itself is so loosely used to define that which we observe.

But fundamentally a wave is just an expression of the flow of energy in time and space. It's observable evidence that energy is flowing. It's clear that traveling waves expresses the flow of energy. And the interference or superposition of two or more traveling waves can create this wave-like thing we observe and call a standing wave. The standing wave looks like a wave and is indeed caused by energy flow, so why not call it it a wave? Can you think of a better name that might more clearly define it?

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  • $\begingroup$ A name for that can be :Chain oscilating particles! Its more like oscilations than some thing propagating. In my attitude waves have this property that can reach some where . But standing waves dont move .so the cannot transfer information $\endgroup$ – adel Feb 1 '16 at 16:25
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    $\begingroup$ @adel so if we were to agree that to be a wave it needs to travel somewhere, then why do some people insist on appending the prefix traveling as in traveling waves? If I observe a standing wave it does appear to move, and it does travel - within a bounded region. At least you can say its constituents are traveling. I do however agree the traveling wave is an oscillation - a resonance caused by trapping the wave within the bounded region. $\endgroup$ – docscience Feb 2 '16 at 2:17
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$f(x-vt)$ isn't the general formulation of a wave, but is the general expression for a travelling wave. Also, a standing wave can be transverse or longitudinal (on a guitar string or inside a laser cavity it is transverse, inside a flute it is longitudinal).

The reason you can hear the sound of a flute is because some of the energy coming from the standing wave radiates outside of the cavity in the form of travelling spherical waves.

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  • $\begingroup$ But i think we findout transverse or longitudianl wave by means of their direction , but satanding waves have no direction to propagate,if you say that standing waves in string is a transverse wave ,what is your answer if put many of these standing string waves parrelel and on each other . Then we can imagine that their prapagation is vertical and vibration is vertical too. So they are longitudinal-@dimitri $\endgroup$ – adel Feb 1 '16 at 15:57
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    $\begingroup$ It indeed does not propagate in any direction, but the two propagating waves the standing wave is made of do propagate in a definite direction, and I believe you should consider this direction to define whether the wave is longitudinal or transverse. $\endgroup$ – Dimitri Feb 1 '16 at 16:03
  • $\begingroup$ Again you can imagine you go some where that you can not see the sources ,you just enter in somewhere and you see the standing waves ,it means you see some particles are just oscilating ,so you can not findout the initial direction of those two or more waves.so i think we can not findout the initial direction of the waves so defining direction and transversy or longitudinal for these oscilating particles are meaningless. $\endgroup$ – adel Feb 1 '16 at 16:17

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