I am a high school student and I am very confused in reflection of waves on string. My confusion is : when a transverse pulse on string reaches a rigid end, how is the reflected pulse inverted in terms of forces (i.e dynamically not mathematically). Some people and even my school textbook says that this is due to Newton's third law, i.e the rightmost particle wants to go upward so it starts to displace the clamp by exerting a very little magnitude of force on it but as the clamp cannot go anywhere it exerts the same magnitude of force on that particle in opposite direction and particle remains at rest. But if it is true then except the rightmost particle which is attached with the clamp, every particle on the pulse already have some velocity, so if net force will become 0 on them then they should continue with the same velocity and the string should break. I want to know by what mechanism their velocities get inverted and they all (particle on pulse) starts to move in opposite direction thus creates an inverted pulse?
I am also confused in another argument related to generation of disturbance (wave) in a string. Suppose that I have generated a simple harmonic wave on string in which all particles are performing simple harmonic motion. Suppose the wave is travelling and it just disturbs the particle which was initially at rest, people says that it disturbs the particle by exerting some kind of force on it, but how can there be any net force on the mean position?