Definition: In this task you will be given a text passage from a trivia quiz. You should choose the category this question belongs to from these categories: History, Science, Social Science, Fine Arts, Literature. You can only choose one category, so if in doubt, please choose the closest match.
Input: One form of this quantity is modified by the principle of least coupling to include the product of charge and vector potential, and its operator can be defined in simple cases as the negative product of i, h bar, and the gradient. In the relativistic four-vector of it, the first term is energy divided by the speed of light, and that form is also included in a generalization of the classical stress tensor. Noether's theorem relates the conservation of this quantity to translational invariance, and its time rate of change is related to force via Newton's Second Law. For 10 points, name this quantity that is conserved in collisions and calculated as the product of mass and velocity, symbolized p.
Output:
Science