Simulations are essential in many areas of science and technology. When problems become more complex, it is difficult to use pure math techniques to predict what will happen. Scientists and engineers then create a mathematical model and use numerical techniques to run the model on a computer.

MyPhysicsLab (link) is a cool website for physics simulations. You can see simulations animating in real time, and be able to interact with them by dragging objects or changing parameters like gravity, mass, etc.

The following simulations are available:

1) Springs
2) Pendulum
3) Combo
4) Collision
5) Roller Coasters
6) Molecules

You need Java (get Java here) to view these simulations.