492 



GENERAL SCIENCE 



laborious hours, are done to-day in a much shorter time by machines. 

 Pumps, vacuum cleaners, sewing machines, dynamos, motors, auto- 

 mobiles, mowing machines, harvesters, and hundreds of other labor- 

 saving devices in the home and out of the home make this age an 

 age of machinery. 



Simple Machines. One of the simplest machines may be seen 

 in the crowbar, or scale. Such machines as these are called levers. 

 They are divided into three distinct classes first class, second 

 class and third class. 



Fulcrum PA Force 







of tke Second Ccxss 



Fulcrum 

 ^Fulcrum 

 \t 



Can Opener 



Fruit Press 



Force 



1 - Lemon Squeezer 



FIG. 371. 



First Class Lever. The first class may be represented by the 

 crowbar, which has been already mentioned. The crowbar is placed 

 over a rock or log, one end under something which we wish to lift, 

 and force is applied in a downward direction at the other end. 

 The rock or log on which the crowbar is resting is called the 

 fulcrum. The thing to be lifted is called the weight, and the force 

 applied at the other end is called the power. 



Second Class Lever. The second class lever may be represented 

 by a nut cracker. Here the power is applied at one end, and the 

 fulcrum is at the other end. The weight (the nut) is between the 

 power and the fulcrum. 



