What does it mean that all points between two adjacent nodes in a standing wave oscillate in phase? I sort of get what in phase means, it means that the peaks and troughs etc of 2 waves align. But how can we say that a single standing wave is in phase? Can someone please explain to me what it means that "that all points between two adjacent nodes in a standing wave oscillate in phase?" And please, try to do this at the level of a high school sophomore who still hasn't learnt Calculus based physics. Thank you.
[Physics] What does it mean that standing waves oscillate in phase
classical-mechanicsharmonicswaves
Related Solutions
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.
They do cancel each other when the peaks of one coincide with the troughs of the other, but since they move in opposite directions, this only happens at specific moments in time (every half period). At other moments (one fourth period later), the peaks of both waves will coincide (and so will their troughs).
In the figure above, the red and green wave move in opposite directions, the blue wave is the sum of both. If the red and green wave moved in the same direction and the phase difference was 180° (meaning peaks of one coincide with troughs of the other), they would indeed cancel each other out at all times.
(image by Yuta Aoki, wikipedia commons)
Best Answer
It means that all those points go up at the same time and down at the same time.
The do not go equally high up and down. Their amplitudes are different. But they do it at the same time nevertheless.
For general waves, in-phase means that the points of two waves progress (move) equally. They "follow each other" perfectly. In standing waves, this boils down to the points not progressing, but still "following each other" by rising and falling equally.