Here is another applet about circular motion.
It was designed to illustrate relation/constraint for circular motion: a=V[sup]2[/sup]/R.
[color=red]Red[/color] arrow is the instance velocity ,
arrow with color "[color=#f0f]magenta[/color]" is
The [color=blue]blue[/color] arrow is which is always pointing toward the center.
so It's length ,