The Radius and Velocity Vectors

Both the radius and the velocity vectors are shown here. The radius is drawn in red, the velocity in blue. Notice that the velocity vector is perpendicular to the radius vector at all points on the orbit. |

The velocity vector is perpendicular to the radius vector.

The radius and velocity vectors are always perpendicular for circular motion.

The velocity vector rotates.

It is not difficult to see that the radius vector rotates as the object orbits. Notice, too, that the velocity vector is also rotating. In fact, both it and the radius vector rotate through an equal angle for any portion of the orbit.