Force is a vector quantity, having both magnitude and direction.
The magnitude of a force is measured in units such as the pound, dyne , and newton , depending upon the system of measurement being used. An unbalanced force acting on a body free to move will change the motion of the body. The quantity of motion of a body is measured by its momentum , the product of its mass and its velocity . Since mass is constant at ordinary velocities, the result of the force is a change in velocity, or an acceleration , which may be a change either in the speed or in the direction of the velocity. Two or more forces acting on a body in different directions may balance, producing a state of equilibrium .