text: This quantity's eigenfunctions are complex exponentials with a constant factor of one divided by quantity "2 pi times h-bar" all raised to the three-halves power.
full_question: This quantity's eigenfunctions are complex exponentials with a constant factor of one divided by quantity "2 pi times h-bar" all raised to the three-halves power. In Planck units, this quantity is given by the square root of h-bar times speed of light cubed divided by the universal gravitational constant. The time derivative of its expected value appears on one side of Ehrenfest's theorem. This quantity is squared in the quantum operator for kinetic energy; its own operator is equal to h-bar divided by i times the gradient. For massless particles, special relativity gives this quantity as energy divided by the speed of light. If position is precisely known, this quantity cannot be according to Heisenberg's uncertainty principle. For 10 points, name this conserved quantity equal to mass times velocity.
first_sentence: This quantity's eigenfunctions are complex exponentials with a constant factor of one divided by quantity "2 pi times h-bar" all raised to the three-halves power.
raw_answer: linear momentum [do not accept or prompt on "angular momentum"]