Real-Time Physics Simulation Forum

I'm pretty comfortable using Bullet, on a very basic level, it does all I need for now and most of my usual physics systems have ported across quite easily. I've used a lot of different Physics engines at whatever level my project needed. But I don't have an especially good grounding in maths or physics, just high school and programmers knowledge, I can generally do everything I need for my projects and tend to learn new things when I need them, but I'd like to improve and Bullet seems pretty solid and easy to get into.

I wonder if there are any good books or online tutorials available for people who want to dive a bit deeper into it?