Force is an effect that changes, or tends to change, the state of rest or uniform motion of an object. The unit of force is the newton (N). 1 N is the force that will produce an acceleration of 1m/s2 when applied to a mass of 1 kg that is free to move. All of the features of a force can be represented graphically by a line. The line is drawn so that its length represents the magnitude of the force. When two forces act at a point so that both are directly in line their combined effect can be found by adding the forces together. If three concurrent, coplanar forces are in equilibrium, two of the forces may be represented by two sides of a parallelogram. If the parallelogram is completed by drawing in the other two sides, the diagonal drawn from the angular point formed by the adjacent sides will represent the third force in magnitude and direction.