These are a few educational simulations that we have written at various points which may be interesting or useful.

The reason than hot air balloons float and chimneys suck the smoke out of a room, is that when you heat up a gas it gets bigger. So why is that?
What is going on when you do the removing DNA from fruit experiments? find out here:
Osmosis and diffusion are processes vital to life, here is a way of looking at it from the point of view of the particles.
Ok the moon is a great big enormous lump of rock, and it is up in the sky, why doesn't it fall down?
Why does the moon change shape from a circle at full moon, to a urrr... moon shape, and sometimes disappear all together?
A simulation of planets moving under gravity. Have a play.
If you accelerate something you must be applying a force to it. Try moving the rabbit around at different speeds and accelerations and see how the force you are applying changes.
A simulation of a hammer and a nail to show why you have to hit nails.