What knowledge should I have under my belt before getting into AS physics?
A GCSE knowledge of Physics at a grade A (in my opinion)
Good knowledge of basic trigonometry (sin, cos and tan functions), cosine rule, sine rule and use these to solve unknowns in triangles. (This will be used a lot in vector problems)
Basics of calculus in mathematics. (eg dy/dx is the rate of change of the variable y in respect to x)
Good mathematical manipulation, including the use powers, roots etc.
Basic algebra, and good unknown solving (EG Simultaneous equations)
(I've just finished A2 Physics at an A grade fyi) Good Luck!