Constant Velocity occurs when there is no net force on the object, that is the external force is equal to force of kinetic friction. Motion on an inclined plane A common problem presented in introductory physics classes is a block subject to friction as it slides up or down an inclined plane. This is shown in the free body diagram to the right. The component of the force of gravity in the direction of the incline is given by: The normal force (perpendicular to the surface) is given by: Therefore, since the force of friction opposes the motion of the block, To find the coefficient of kinetic friction on an inclined plane, one must find the moment where the force parallel to the plane is equal to the force perpendicular; this occurs when the block is moving at a constant velocity at some angle or Here it is found that: where is the angle at which the block begins moving at a constant velocity References Classical mechanics