An infrared-safe jet clustering algorithm invented by Matteo Cacciari takes the reciprocal of a component of this quantity. A parton distribution function gives the probability density of finding a parton at a given value of a component of this quantity. (10[1])The transverse component of this quantity is large for “hard” interactions like hadronization (-5[1])and small for “soft” interactions. The scattering vector q represents the transfer of this quantity, where this quantity (10[1])equals Planck’s constant times wavevector. (10[2])In the analysis of scattering (10[1])problems, the center of mass (10[1])frame is often generalized by an inertial frame named the center of this quantity. (-5[1])Both elastic and inelastic collisions (10[1])obey this quantity’s (10[1]-5[1])conservation law. For 10 points, (-5[1])name this quantity equal to mass times velocity. (10[4])■END■