Meccanica in casa e all'aperto

Le prime righe

Fig. 6. Double lever as scales "Here's another sketch (Fig. 5), in which A,B,C, together show the lever, also the power A, the fulcrum B, and the weight C. If I should place the fulcrum B so that it would be in the middle between the ends A C, there would be what is termed an equilibrium between the weight and the power, and if they are equal there will be a perfect balance maintained. It is on this principle that scales for druggists are made, the lever being suspended in the centre of its length, as I show in the sketch (Fig. 6). These scales are very nicely adjusted, and the chains and receivers are made as nearly alike in weight as possible. The arms of the lever being of equal length from the centre, or pivot, permit the lever to stand in a perfectly horizontal position, unless disturbed by having a weight placed in either one or other of the receivers. In this case, the pivoted point P is the fulcrum, and the two points O and X may be taken as the power and the weight. If one pound is placed in the receiver at O, it will tip the scale down, and that will become the weight, while any commodity placed in the receiver at X, until the lever is again brought level, or horizontal, may be called the power. As another illustration I'll tell you of something that took place the other day. In the vacant lot are several piles of bricks, stones, and planks. George, seeing this, took one of the planks and threw it across several others, making a 'Teeter Tauter,' or, as some children call it, a 'Seesaw.' He balanced the plank nicely, and then invited Jessie and her cousin to sit on it, one at each end. The two girls were about the same weight, and George held the plank until both were seated. It remained level and balanced, until George got on the top of it, and stood on the