8.S.I.B.2

Unbalanced forces cause changes in velocity. If an object is subject to two or more forces at once, the effect is the net effect of all forces. The motion of an object does not change if all the forces on it are in balance, having net effect of zero. The motion of an object changes in speed or direction if the forces on it are unbalanced, having net effect other than zero. To achieve a given change in the motion of an object, the greater the mass of the object, the greater the force required.