Entering the world of physics…. is always a bit tough. Although simulating a turntable mechanism is not a very tricky mechanism to mimic (I’m currently just copying the inner works of a direct-driven motor). The AS3 physics engine is Box2Das3 which is a direct port of the Box2d original one, written in C++.
(this object already behaves pretty much like a moving motor that can be applied with force(s) from the user interaction)
After laying out a few drawings for understanding the forces in the equation, my first few attempts generated a quite interesting result, although there’s a lot of configuration to do to allow the torque to behave like a turntable model motor, pitch adjust, normalize velocity, compensate brake power, shutdown feature, etc… (and maybe include a platter for fine tuning the speed…)