The double-pendulum is a great example of chaos in action and how the ever slightest change in initial conditions causes the system to get out of whack pretty quickly. Another cool example are the spaghetti models used to predict the track of hurricanes. Several may all point in one general direction, but one is totally off because of a slight change in the model. Even with our advanced supercomputers, we are not very precise when it comes to weather forecasting. Back when hurricane Charlie hit Florida several years ago, my friend evacuated to Orlando thinking we were going to have a direct hit (Pinellas/Tampa), but in the last 24 hours it moved inland and hit Puta Gorda. We had nothing where we were, but Orlando was actually hit pretty hard.