COEFFICIENT OF FRICTION
In our studies of Newton's laws, we often used idealized situations in which we neglected the effects of friction. However, in practice, friction almost always exists. If friction could be considered a negligible force in the game of pool, the balls would never stop moving. The friction coefficient is a function of the force of weight and the normal force as described by the equation:

After an initial force was applied on the ball by the pool stick, there were three forces acting on it: (1) the force of weight (mass*gravity) pulling in the negative y direction; (2) the normal force applied by the table acting on it in the positive y direction; (3) the force of friction between the ball and the table, causing the ball to have a negative acceleration.