This animation enables you to compare the properties of a fixed pulley with those of a pulley system. One pulley enables you to change the direction in which a force acts. Associated with one or several other pulleys (compound devices) the pulley enables one to reduce the force needed to lift a mass.
Note that the distance the mass is displaced is reduced by a factor identical to the factor of reduction of the force. Thus, for a system with two pulleys, the force needed is halved, but the so is the height of displacement. Energy is thus conserved.
Note: The friction and weight of the cord and the fasteners is ignored.