Equations of motion force the object exerts. Replacing momentum by mass times velocity, the law is also written more famously as since is a constant in Newtonian mechanics. Newton's second law applies to point-like particles, and to all points in a rigid body. They also apply to each point in a mass continua, like deformable solids or fluids, but the motion of the system must be accounted for, see material derivative. In the case the mass is not constant, it is not sufficient to use the product rule for the time derivative on the mass and velocity, and Newton's second law requires some
Angular velocity is formula_5, and the linear velocity is formula_6, so that formula_7. In the general case of a particle moving in the plane, the angular velocity is measured relative to a chosen center point, called the origin. The diagram shows the radius vector r from the origin "O" to the particle "P", with its polar coordinates formula_8. (All variables are functions of time "t".) The particle has linear velocity splitting as formula_9, with the radial component formula_10 parallel to the radius, and the cross-radial (or tangential or circular) component formula_11 perpendicular to the radius. When there is no radial component, the