Machines 



25 1' 



The Steam Engine. The steam engine is an illustration of 

 a complex machine built up by combinations of simple machines. 

 Like all heat engines it transforms heat energy into mechanical 

 energy. The modern steam engine has developed from one invented 

 in the latter part of the 18th century by James Watt. It depends 

 for its efficiency on the energy released by molecules of water 

 when heated. 

 Heat causes 

 the molecules 

 to become 

 very active so 

 that some of 

 the water 

 changes to 

 steam, ex- 

 pands, and 

 exerts great 

 pressure. This 

 steam when 

 conducted into A STATIONARY STEAM ENGINE 



the cylinder of a steam engine comes into contact with a body 

 called a piston, a cylindrical body which can move back and forth 

 within the cylinder. By allowing the steam to enter the cylinder, 

 first at one end and then at the other, its expansive force pressing 

 against the ends of the piston causes it to move back and forth in 

 the cylinder. The motion thus generated is communicated to a 

 shaft with which the piston is connected, and the motion of the 

 shaft is passed on to other parts of the machine. 



The stationary steam engine is extensively used in driving 

 machinery in factories. It is largely responsible for modern 

 manufacturing methods. 



Friction. Friction usually reduces the working efficiency of 

 a machine. We know how difficult it is to run a lawnmower, or 

 any household machine with movable parts, unless it is well oiled. 

 The tiny roughnesses of the metal surfaces which rub each other 

 prevent easy movement and cause waste of energy. Oiling, how- 

 ever, coats these surfaces with free-moving oil particles which 



