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| A pulse is sent down the machine. When it reaches the other end, which is free to move, it is reflected. | Video. | Real Video | Still. |
| A pulse is sent down the machine as above. This time, the end of the machine is rigidly clamped. The wave is reflected with inversion from the clamped end. | Video. | Real Video | Still. |
| Pulses are sent from each end and meet in the middle. The two waves add when they overlap, giving a momentarily larger displacement. | Video. | Real Video | Still. |
| When sinusoidal waves of the same frequency traveling in opposite directions
meet, they create a patter called standing waves. Standing waves do not
appear to move left or right, they just oscillate up and down.
A plucked string, an organ pipe, and our wave machine all can exhibit standing waves resulting from the interference of multiply reflected waves traveling in opposite directions. Waves that can make a round trip of the string, pipe, or wave machine and arrive at the starting point in phase produce stable, long-lasting patterns. If end of the wave machine is unclamped, the wave is reflected without inversion, and there is an antinode at each end. Shown in the accompanying video is the lowest frequency mode of this kind. The instructor simultaneously pushes one end up and the other end down. A node (a spot of zero displacement) appears at the center. |
Video. | Real Video | Still. |
