For example, if a mason desires to move a large piece of stone forward, instead of bearing down upon the lever to raise the stone up a little, he sticks his crowbar into the ground under the stone and at the same time pushes forward (Fig. 11). In this way he moves the stone onward little by little, the ground being the fulcrum. The same principle of leverage applies to the opening of doors or box covers. The oars of boats and the masts of a ship in which the cargo acts as resistance, the bottom of the vessel as the fulcrum, and the sails as the moving power, are also levers of the second class. Nutcrackers (Fig. 12), lemon-squeezers, and devices consisting of two legs joined by a hinge are further illustrations of this class of levers.