운동 에너지
Kinetic energy is the energy of the system's motion, and "vk"2 = v"k" · v"k" is the magnitude squared of velocity, equivalent to the dot product of the velocity with itself. The kinetic energy is a function only of the velocities v"k", not the positions r"k" nor time "t", so "T" = "T"(v1, v2, ...).