SimpleHarmonicMotion
Like ocean waves, these look like they are moving horizontally, but in fact, all the motion is vertical. Each point on each of the two waves moves up and down in simple harmonic motion.Essentially, one of the curves is a sine curve, and the other is a cosine curve. By dragging the black points, you can vary the amplitude and frequency.
For more, see GEOMETRY IN ACTION, Chapter 5.