Imagine two carousel riders on a spinning carousel—what is the relative motion of one rider to another? The relative position of one carousel horse to another describes a circle. Relative to any one carousel rider, the other riders travel in concentric circles.
Animate the time parameter to spin the carousel.
In the left diagram, the red rider follows the blue rider in a circle, separated by a certain angle. The right diagram translates the carousel to show the relative motion of the blue rider to the red rider. When the "relativity of motion" is 1, the translation holds the red rider in a stationary position to show the relative motion of the blue rider. When the relativity of motion is 0, the carousel is not translated. The magnitude of the translation is scaled for values between 0 and 1.
Now, move the "relativity of motion" slider from 0 to 1 to convince yourself that the left and right carousels are translations and that the blue rider actually travels in a circle relative to the position of the red rider.