Stationary waves in a vertical rope

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SUMMARY

This discussion focuses on the production of stationary waves in a vertical rope, highlighting that pulses from both the lower and upper extremities travel with accelerations of g/2 and -g/2, respectively. The participant seeks to derive the equations for stationary waves, questioning the applicability of standard wave functions due to variable velocity. The provided equations include a wave function of the form $$y=A sin(w\sqrt{4x/g}-wt+\phi)$$ and a stationary wave representation $$y_{stationary}=2A sin(w\sqrt{4x/g}+\phi) cos(wt)$$. The conversation suggests analyzing the problem using the partial differential equation $$\frac{d}{dx} \left(T(x) \frac{\partial y}{\partial x} \right) = \mu \frac{\partial^2 y}{\partial t^2}$$ with appropriate boundary conditions.

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jaumzaum
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I was wondering if we could produce stationary waves in a vertical rope. There is a nice result we can get from a vertical rope that the pulse created from the lower extremity travels upwards with acceleration g/2 and the pulse created in the upper extremity travels downwards with acceleration -g/2. I was trying to get the equations of the stationary waves in a vertical rope (that is, if they exists), but I don't know if the most simple wave functions hold anymore.

For example, I was taught any wave can be written in the form:
$$y=f(x-vt)$$
But here the velocity is variable, so can we still write the above equation?
Also, will the amplitude remain constant?

I will write the result I got, but I don't know if they are correct, can anyone help me figure this out?
For the wave:
$$x=\frac{gt^2}{4}$$
$$\alpha=w\sqrt{4x/g}-wt+\phi$$
$$y=A sin(w\sqrt{4x/g}-wt+\phi)$$

For the stationary wave:
$$y_{stationary}=2A sin(w\sqrt{4x/g}+\phi) cos(wt)$$
 
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I am not sure of acceleration you state. Wave propagates with increasing speed ?
I am not sure vertical, horizontal or any direction of rope length make difference of the vibration.
 
I haven't checked this but maybe you can analyse it with something like$$\frac{d}{dx} \left(T(x) \frac{\partial y}{\partial x} \right) = \mu \frac{\partial^2 y}{\partial t^2}$$where I have taken ##\hat{x}## pointing down and ##\hat{y}## pointing to the right. We could approximate that ##T(x) \approx \mu g(L-x)##, and try and solve the PDE w/ boundary conditions ##y(0) = y(L) = 0##.
 
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