Machines 253 



may be transformed but it cannot be created or destroyed. 

 Energy never comes from anything that is not energy. 



It is reported that the United States Patent Office receives 

 many applications for patents on machines which will work con- 

 tinuously without the use of fuel or the acquirement of energy 

 from any other source. Such machines are called perpetual mo- 

 tion machines. The principle of the conservation of energy shows 

 that a perpetual motion machine is impossible because it requires 

 the creation of energy out of nothing. 



SUMMARY 



A machine is a device for transforming and applying energy 

 and for making work easy or less burdensome. Work means the 

 overcoming of resistance. 



The mechanical advantage of a machine is its efficiency as 

 measured by the force it exerts divided by the force applied to it 

 to make it work. 



There are six simple machines, the lever, the pulley, the wheel 

 and axle, the inclined plane, the wedge, and the screw. 



The lever is a rigid rod arranged to turn on a fixed support 

 called the fulcrum. 



Levers are divided into three classes, according to the relative 

 position of the fulcrum, the effort and the weight. 



The pulley and the wheel and axle are modifications of the 

 lever. 



The inclined plane is a plane surface set at an oblique angle 

 to the horizon. 



The wedge and the screw are modifications of the inclined 

 plane. 



Friction usually reduces the working efficiency of a machine. 

 In many of our ordinary activities, however, friction is helpful or 

 necessary. 



FACT AND THOUGHT QUESTIONS 



1. What is a machine? Give examples. 



2. Define: (a) work, (b) force, (c) energy, (d) power, (e) friction. 



3. Name and describe the two basic forms of machinery. 



4. What are the six simple machines? 



5. Describe the lever and give examples of each class. 



