Caroline. And of what nature are the other two kinds of levers?
Mrs. B. In levers of the second kind, the weight, instead of being at one end, is situated between the power and the fulcrum, ([fig. 6.])
Caroline. The weight and the fulcrum have here changed places; and what advantage is gained by this kind of lever?
Mrs. B. In moving it, the velocity of the power must necessarily be greater than that of the weight, as it is more distant from the centre of the motion. Have you ever seen your brother move a snow-ball by means of a strong stick, when it became too heavy for him to move without assistance?
Caroline. Oh yes; and this was a lever of the second kind, ([fig. 7.]) the end of the stick, which he thrusts under the ball, and which rests on the ground, becomes the fulcrum; the ball is the weight to be moved, and the power his hands, applied to the other end of the lever. In this instance there is a great difference in the length of the arms of the lever; for the weight is almost close to the fulcrum.
Mrs. B. And the advantage gained is proportional to this difference. The most common example that we have of levers of the second kind, is in the doors of our apartments.
Emily. The hinges represent the fulcrum, our hands the power applied to the other end of the lever; but where is the weight to be moved?
Mrs. B. The door is the weight, which in this example occupies the whole of the space between the power and the fulcrum. Nut crackers are double levers of this kind: the hinge is the fulcrum, the nut the resistance, and the hands the power.
In levers of the third kind ([fig. 8.]) the fulcrum is again at one extremity, the weight or resistance at the other, and the power is applied between the fulcrum and the resistance.