To develop the concept that interactions between objects are expressed as forces. To identify a number of common forces and understand how they can be quanti ed. To associate the acceleration of an object with the sum of all forces acting on the object. To become familiar with the fundamental rules by which forces are connected to motion. To develop a systematic approach to solving force problems, including the use of free-body diagrams. Whenever two objects interact with each other, they in uence each other"s motion. The nature of that interaction can vary immensely; they can affect a change in each other"s speed, they can collide and redirect their motion-or their interaction could serve to simply maintain a certain motion. Whenever two objects interact, we describe that interaction as a force. The forces that act on an object are connected with the motion of the object.