Forces are important because they determine how the motion of an object changes. To determine how forces affect an object's motion, we must first find the net force on the object. The net force is the vector sum of all the forces acting on an object. Adding vectors requires us to take into account the direction of the vectors. For example, if two forces both act in the same direction, we can treat both magnitudes as positive. A force of 10 N to the right and a force of 20 N to the right, both on the same object, give a net force of 30 N to the right on that object. If two forces act in opposite directions, one force can be considered positive and the other negative. Imagine now that we have a 10 N force to the right and a 20 N force to the left on the same object. If we assign the positive direction as to the right, the net force is 10 N + (20 N) = 10 N. This means the magnitude of the net force is 10 N, and, because the result is negative, the net force points to the left. If