The position of a single particle moving in ordinary Euclidean 3-space is defined by the vector q = ( x , y , z ) , and therefore its configuration space is Q = R 3 . It is conventional to use the symbol q for a point in configuration space; this is the convention in both the Hamiltonian formulation of classical mechanics, and in Lagrangian mechanics. The symbol p is used to denote momenta; the symbol q ˙ ˙ = d q / d t refers to velocities.