An equation, based on the second of Newton’s laws of motion, that governs the motion of a particle. In vector form, the equation is , where F is the total force acting on the particle of mass m. In Cartesian coordinates, this is equivalent to the three differential equations , and , where F = F1i + F2j + F3k. In cylindrical polar coordinates, taken here to be (r,θ,z), it is equivalent to , , and , where now F = F1er + F2eθ + F3k, and er = i cosθ + j sinθ and eθ = −i sinθ + j cosθ (see radial and transverse components).