Observe the behavior of the circle by moving the sliders. Attach the wheels on the car by moving the sliders. r1 and r2 for the size of it, a1 and a2 for the direction left and right; b1 and b2 for the direction up and down.

A circle is a locus of points in a plane, that are located at a constant distance from a fixed point. The fixed point is called the center and the constant distance is called the radius.
The formula of a circle is:
(x-h)^2+(y-k)^2=r^2
In the diagram above, h= a1 and a2; k= b1 and b2; and r^2= r1 and r2 in the formula of a circle. Notice how each affects the circle.