You may think that simulating physics in code is complicated and hugely demanding in terms of computer resources. Sure, if you want to model real-life physics for engineering projects or NASA missions, then you have to be pretty damn accurate. But to just produce some cool effects, there are techniques for approximating physical phenomena such as gravity and drag that are so simple that the code will run at lightning speed.
You can produce a wide range of different effects with only minor adjustments. I've used Flash particle systems to produce electrical sparks, swarms of bats, fireworks, dripping goo, fire and sweat! With a little imagination you can have a lot of fun. This tutorial is a great way of getting into programming simple physics and movement. More importantly, it shows that you can produce some beautiful particle effects with straightforward ActionScript.