Whenever we lift something, push something, or otherwise manipulate anobject, we are exerting a force. A force is defined very practically asa push or a pull—essentially it’s what makes things move. A force is avector quantity, as it has both a magnitude and a direction.
In this chapter, we will use the exampleof pushing a box along the floor to illustrate many concepts aboutforces, with the assumption that it’s a pretty intuitive model that youwill have little trouble imagining.
Physicists use simple pictures called
free-body diagrams to illustrate the forces acting on an object. In these diagrams, the forces acting
ona body are drawn as vectors originating from the center of the object.Following is a free-body diagram of you pushing a box into your newcollege dorm with force
F.
Because force is a vector quantity, itfollows the rules of vector addition. If your evil roommate comes andpushes the box in the opposite direction with exactly the samemagnitude of force (force –
F), the net force on the box is zero
