HELP!!!proof that a=v^2/r in NON-uniform circular motion Most of the proofs I have read especially the geometric approach assume that the speed is constant, so it mustn't apply for non-uniform circular motion. Some proofs use calculus and starts from the position vector and differentiates it to get the velocity and differentiates again to get the acceleration vector. What i can't understand with this proof is that the magnitude of the acceleration vector becomes exactly equal to v2/r even if it wasn't assumed in the proof that the speed is constant. If the speed isn't constant then the magnitude of the acceleration vector must be more than that. Here is the link for the proof: http://www.youtube.com/watch?v=YRBRarbMCyE&feature=relmfu Is this proof just for uniform circular motion?? Help please!!!!