The inclined plane
A heavy load may be raised more easily by pulling it along a sloping surface than by lifting it vertically. Heavy packing cases are often loaded into vans by hauling them up an incline formed by two stout planks held apart by iron stays (Fig. 8.9). It is believed that the large blocks of stone used in the construction of the Egyptian pyramids were raised into position by dragging them, on rollers, up a long ramp of earth. On completion of the building, the earth was taken away. In Fig. 8.10 a load is being pulled up an inclined plane AB. In order to raise the load through a vertical height h, the effort has to be exerted through a longer distance equal to the length of the plane I. It must be clearly understood that, because the weight of the load acts vertically downwards, the distance through which the load is overcome is h and not l.
The mechanical advantage may be obtained by applying the law of conservation of energy (or principle of work). We neglect the work done against friction and sume that the work done on the load is equal to the work done by the effort.