Consider a hockey puck at rest on ice. Apply a force, and it starts to moveit accelerates. When the hockey stick is no longer pushing it, the puck moves at constant velocity. Apply another force by striking the puck again, and again the motion changes. Applied force produces acceleration. Most often, the applied force is not the only force acting on an object. Other forces may act as well. Recall, from Chapter 2, that the combination forces acting on an object is the net force. Acceleration depends on the net force. To increase the acceleration of an object, you must increase the net force acting on it. If you double the net force on an object, its acceleration doubles; if you triple the net force, its acceleration triples; and so on. This makes good sense. We say an object's acceleration is directly proportional to the net force