the operation of finding the vector quantity R equal to the vector sum of the vectors representing the forces of a given system. R is known as the resultant of the system of forces. The operation is performed according to the rule for addition of vectors—in particular, by plotting a polygon of forces. The mechanical meaning of the quantity R is determined by theorems of statics and dynamics. Thus, if the system of forces acting on a solid has a resultant, the system is equivalent to the resultant. When any mechanical system moves, its center of mass moves as would a point mass whose mass is equal to the mass of the entire system and is under the action of a force equal to the resultant of the external forces acting on the system.