[quote author=Fu-Kwun Hwang link=topic=190.msg813#msg813 date=1118130338]
A small sphere of mass m is attached to the end of a cord of length R, which rotates under the influence of the gravitation force in a vertical circle about a fixed point.
This applet shows how the speed of the sphere and the tension of the cord change.-*-
[/quote]

Yes, a cord/string version would be a good addition to your collection of simulation.

and the words in the top post should be rod instead of cord, because T can be negative to become support force on the mass m.
if cord=string then model would change to projectile motion when T - m*g*cos(theta) < m*v^2/r imply  T = 0 and the motion is under gravity field only.

the difference is subtle but some sg school teacher use this example to trick the students during level test.