LEVERAGE 29 



31. Examples of Levers of the First Class. Another 

 example of a lever of the first class is the use of the fire poker 

 with the bar of the grate serving as a fulcrum. When a 

 lever consists of two parts fastened by a rivet, it is called 

 a double lever. Scissors, pincers, and forceps are all examples 

 of such a lever ; the rivet serves as a fulcrum. 



The scale beam used in weighing is also a simple lever. 

 The arms on each side are of equal length and are suspended 

 over the center of support. The axis at the point of suspen- 

 sion is sharpened to a very fine, sharp edge, so that when 

 weights are placed in the scales, the beam may turn with as 

 little friction as possible. When the arms are not of equal 

 length, the scales cannot weigh accurately, although the 

 beam may seem fairly balanced and the weights true. If 

 one arm is 8 in. long and the other only 7^ in. the scale will 

 balance with a 1-lb. weight on the short arm and 15-oz. on 

 the long arm. Thus the customer of a merchant who uses 

 such a scale loses an ounce in every pound. The deceit can, 

 of course, be discovered by changing the weight and material 

 to the opposite scales. In some cases where the beams of 

 scales are not accurate, the articles to be weighed are put 

 in one pan and balanced by weights; the article is then put 

 in the other pan and balanced again. The correct weight 

 is found by taking the square root of the product of the two 

 weights. 



32. Levers of the Second Class. In the second class 

 lever the weight and force are on the same side of the ful- 

 crum, the weight being placed between the force and the 

 fulcrum. 



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 



