These demos illustrate cool principles in Dynamics.

What happens if you…

pull backwards on a bicycle pedal? This is a good puzzle for constrained motion.

Or create a system that only applies a coriolis acceleration?  Great for looking at different components of polar acceleration

Or drop something so that it falls FASTER than gravity?

Great resources for other demos may be found at these sites:

• The most exhaustive and impressive group of demos can be found at :  Wolfram Demonstrations Project
• Great (but mostly very elementary) more polished simulations can be found at PHET.