Lets say that there is a rectangular box on a horizontal surface, with no air resistance on it. If the applied force required to get the object moving is greater than the static friction, Fa>Us* Fn, then the object starts moving. However, the Static Friction is almost always greater than the Kinetic Friction, Us> Uk. That means that the applied force is more than the resulting kinetic friction from sliding: Fa > Uk. If so, then how does an object decelerate if the force is positive (in the direction of movement)? In summary, how does an object stop moving if the sliding friction is lower than the applied force (such as a book sliding down a table)? A force only changes the acceleration. In order to decelerate, the kinetic friction must exceed the applied force and therefore, static friction as well.