Suppose a man has to push an object up an inclined surface. He should apply a force to balance other forces so that it does not topple over. All the forces on the object can be graphically visualized using a free-body diagram. For this, replace the object by a simple alternative like a square or a circle, or a point in the case when its shape and size are not important. Replace each force with a line arrow pointing in the same direction as the force and having a size that reflects its magnitude. Include only those forces that affect the system and not those exerted by the system on the surrounding. In our present example, the refrigerator is the object of interest. So, in the free-body diagram, the refrigerator is drawn as a square. The forces acting on it are the gravitational force due to its mass, the normal force, the frictional forces due to the inclined surface, and the force applied by the man. The force exerted by the refrigerator is not considered.