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In the book 'Principles of Physics' by Resnick,Halliday and Jearl Walker,the opening para of derivation of wave speed from Newton's Second Law is such:

Let us consider a symmetrical pulse moving from left to right along a string of speed $v$. For convenience,we choose a reference frame in which the pulse remains stationary;i.e,we run along the pulse,keeping it constantly in view.In this frame,the string appears to move past us,from right to left with speed $v$

My confusion is :

If I am moving with the pulse,I should moving left to right with velocity $v$ wrt the reference for which pulse is moving left to right with velocity $v$.

So I should have zero speed wrt pulse and string both.

How can the string be moving right to left with speed $v$ if I am stationary to the pulse?

enter image description here

Are not the velocity of the pulse and velocity of the string are in the same direction and of same magnitude?

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In the first instance, we are stationary w.r.t. the string, and the pulse propagates from left to right as follows:

enter image description here

In the second instance, we are stationary w.r.t the pulse, and so the pulse appears in the same place while the string appears to move from right to left (look at the end points of the string):

enter image description here

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If the pulse is moving to the right relative to the string (and you), then string (and you) are moving to the left relative to the pulse. It's like when you are in a car; if you are moving forward relative to the landscape, the landscape is moving backward relative to you. The next time you are in a car traveling at a constant speed along a straight road, imagine that the car (and you) are stationary and the landscape is moving backward. It's a weird feeling.

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