Usually several forces act on an object at the same time. They can be replaced by a single force that has the same effect as all the original forces acting together. This single force is called the resultant force.
To find the resultant of two forces that act in a straight line, take their directions into account. If the forces act in the same direction, add them. If they act in opposite directions, subtract the smaller from the larger. The resultant acts in the direction of the larger force. For example, a 12 N push to the right and a 5 N push to the left give a resultant of 12 − 5 = 7 N to the right. Two forces of 6 N and 4 N that both act upwards give a resultant of 6 + 4 = 10 N upwards.
If two equal forces act in opposite directions, the resultant force is zero and we say the forces are balanced. An object with a resultant force of zero has no change in its motion: if it was at rest it stays at rest. If the forces are unbalanced, the resultant force is not zero and the motion of the object changes.
