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SOME SIMPLE MACHINES IN THE HOME 



we must apply more force than the resistance to be over- 

 come. Then why use such a machine? There is another 

 advantage for which some machines are used, that is, speed 

 and distance moved. The advantage of levers of the 

 third class is that of speed or distance covered. Notice 

 how this is shown in the sugar tongs. 



How we weigh things. A pair of scales at home is a 

 necessary thing, for it may save more than its cost many 

 times over in checking up the weight of groceries and other 

 materials. Most scales in use are dependent on the prin- 

 ciple of the lever. 

 In the scales in the 

 picture, can you tell 

 whether you would 

 get more or fewer 

 apples if the sliding 

 weight were placed 

 at point A or at 

 point B ? Can you 

 explain why ? An- 

 other household scale not dependent on the principle of the 

 lever is the spring balance. To explain such a scale, let 

 us suspend a coiled wire with a pointer fastened at the 

 bottom. Let us now fasten to the wire, weights weighing 

 10, 20, and 30 grams respectively. As the weights pull 

 the wire down, mark the position of the pointer on the 

 scale representing 10, 20, and 30 grams. We might con- 

 tinue this scale to make several more marks, and as long 

 as the elasticity remained in the wire, we could then use 

 this for weighing purposes. This is the principle of the 

 spring balance or postal balance used for weighing letters. 

 The lawn mower. If you have pushed a lawn mower 



Principle of the lever used in weighing. 



