This is a great visual that connects circular motion to linear motion in perpendicular directions.

Leave the "Lines" box unchecked. Click the "play" button at the lower left to start the animation. Observe how the two pairs of lines move independently from one another. Changing the "radius" slider changes the distance the line pairs move.[br][br]Now check the "Lines" box. The segments are extended by thin lines, and the intersections of the lines trace out circles. Your brain might now convince you that there is one diamond shape moving in a circle, instead of two sets of parallel segments moving linearly.