I'm having trouble with the explanation that a standing wave in a string is the superposition of traveling waves.
(source: physicsclassroom.com)
The nodes in the diagram above are points where the particles of the string's medium undergo zero displacement, i.e. they do not move at all. But if they do not move, how is the disturbance of (any internal traveling wave) propagated past the node?
The usual explanation for how a wave is propagated is that when one particle is disturbed (say, moved up), it exerts a pull on another, which in turn exerts a pull on the next one, and so on. In other words, to exert a pull or push on the next particle there must be some movement/disturbance of the previous one. But the particle(s) at the node point do not move at all, so how does the disturbance of a traveling wave propagation pass through them? (I'm trying to understand the picture in terms of the mechanical forces between particles).
Best Answer
The nodes do not change position, but the forces on them change. The forces are the cause of displacement.
It may help to use a slinky instead of a string. The slinky stretches into a sinusoidal shape and shrinks to a line. As the point at the node is pulled up by one by one traveling wave and equally down by the other, it stretches. As the slinky shrinks, so does the stretching at the node.
The pattern of stretching does pass through the stationary node.