# waves in a moving string

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#1
hello i have to do a project on waves in a moving string and the information i find on the internet or the library is either too complicated or just not what im looking for. can anyone help me with any sources or information on this or waves in moving media in general? Thank you
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3 years ago
#2
when you say waves in a moving string is this physics? Or a different subject? If it's physics I can help I think
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#3
(Original post by j.woods)
when you say waves in a moving string is this physics? Or a different subject? If it's physics I can help I think
yes! it is physics. any help would be appreciated thank you very much
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3 years ago
#4
okay, when you say moving string what do you mean? Is that progressive or stationary wave?
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#5
(Original post by j.woods)
okay, when you say moving string what do you mean? Is that progressive or stationary wave?
so there is a string going in a loop powered in a motor and by touching it you create waves that move through the string while the string itself moves
here is an illustrative video:
0
3 years ago
#6
I've never seen it like that before haha but I'm guessing it has got something to do with reflection off the wave, when I wave hits the boundary it is reflected at the same speed and wavelength, the reflected wave then supervises with the original wave but I'm not sure if this info is relevant to this topic haha sorry
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3 years ago
#7
(Original post by siete)
hello i have to do a project on waves in a moving string and the information i find on the internet or the library is either too complicated or just not what im looking for. can anyone help me with any sources or information on this or waves in moving media in general? Thank you
What exactly are you looking for? Look up D'Alembert's solution for the basic solution to a wave moving on a string in 1D.
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#8
(Original post by Ryanzmw)
What exactly are you looking for? Look up D'Alembert's solution for the basic solution to a wave moving on a string in 1D.
what im looking for is for waves on a string that is already moving horizontally. i have been told that the speed of the waves formed on an already moving string would be the speed of the string summed to the speed it would have if the string were stationary. I have no proof of this. i would like any information on the motion of such waves, equations and things.
i have looked up d'alembert's solution and it was helpful but only for a stationary string.
0
3 years ago
#9
(Original post by siete)
so there is a string going in a loop powered in a motor and by touching it you create waves that move through the string while the string itself moves
here is an illustrative video:
That's so cool.
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3 years ago
#10
(Original post by siete)
what im looking for is for waves on a string that is already moving horizontally. i have been told that the speed of the waves formed on an already moving string would be the speed of the string summed to the speed it would have if the string were stationary. I have no proof of this. i would like any information on the motion of such waves, equations and things.
i have looked up d'alembert's solution and it was helpful but only for a stationary string.
(Original post by Ryanzmw)
What exactly are you looking for? Look up D'Alembert's solution for the basic solution to a wave moving on a string in 1D.

assuming a galilean velocity transformation (of the form x' = x-ut), where u is the speed of the medium you can transform the wave equation to a mixed partial differential equation that can be solved via factorisation in the same way as the usual wave equation. mathematically this is done via the chain rule for partial derivatives and working out the expression for the derivative with respect to x in terms of x' and t

the end result is a function of the form f(x-(u-c)t) which can be seen as a simple time translation of the solution to the "ordinary" wave equation having form f(x-ct), where c is the wave speed.

the whole point is that in practice you would never do this since the maths works out so much more easily in the co moving reference frame that is travelling along with the medium so we just do all our calculations in that frame instead.

if you want to dig a bit deeper you'll see that things don't quite work out as nicely as this which is what led to the advent of special relativity but this is a seperate topic entirely
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