FORCE EQUILIBRIUMApplication of Newton's LawsCP-04 Page 12Rev. 0Figure 5 Net ForceThe book remains stationary resting on the table because the table exerts a normal force upwardequal to the weight of the book. Therefore, the net force on the book is zero. If a force isapplied to the book (section B of Figure 5), and the effect of friction is neglected, the net forcewill be equal to the applied force, and the book will move in the direction of the applied force.The free-body diagram in section C of Figure 5 shows that the weight (W) of the book iscanceled by the normal force (N) of the table since they are equal in magnitude but opposite indirection. The resultant (net) force is therefore equal to the applied force (F).APPEquilibriumSince an object in equilibrium is considered to be in a state of balance, it can be surmised thatthe net force on the object is equal to zero. That is, if the vector sum of all the forces actingon an object is equal to zero, then the object is in equilibrium.Newton's first law of motion describes equilibrium and the effect of force on a body that is inequilibrium. That law states "An object remains at rest (if originally at rest) or moves in astraight line with a constant velocity if the net force on it is zero." Newton's first law of motionis also called the law of inertia. Inertia is the tendency of a body to resist a change in its stateof motion.
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