I'm new to the idea of Velocity Verlet Integration, whereas before I was apparently using Euler's method. After finding out about this I returned to an asteroid gravity simulation(whereby every asteroid is gravitationally attracted to every other on) I'd made a while ago and tried to implement the integration. However it doesn't quite work and I get get some odd results. Not insane, but not what I'd expect in real life.
I'm following this tutorial; http://buildnewgames.com/gamephysics/
The code (if it doesn't make sense please ask questions):