Mark Moxon publishes annotated source code and discussions of the algorithms within, for some groundbreaking games on Acorn’s 6502-based computers - look for the Deep Dive sections:
Aviator and Revs both have decent physics engines to go with their graphics.
Corresponding discussions on Stardot.
Previously
A new fully annotated disassembly of Elite (BBC Micro versions)
Backporting the Nürburgring track - Revs on the BBC Micro