UNIT VII. USING MACHINES TO HARNESS ENERGY 



Man's conquest of nature has been a long and 

 difficult struggle. Ages ago, because of his superior 

 intelligence, man learned that by using a crude weapon 

 made of stone he could more easily subdue his ani- 

 mal enemies and that by means of a stick he could 

 more readily move heavy obstacles. These were 

 probably the first attempts to gain an advantage over 

 natural forces. Later the inclined plane helped him 

 to raise heavy loads to greater heights than would be 

 attainable with the crude lever bar of earlier times. 

 The wedge used with the stone axe aided him in split- 

 ting the logs which went into his dugouts and huts. 

 Since then man's progress has been largely a story 

 of continued victories over the resistant forces which 

 surround him. 



The more complicated machines such as the wheel 

 and axle, the pulley, and the screw were developed in 

 later ages long after man had learned the use of the 

 simpler ones. These, in combination with the others, 

 form a large part of the foundation of the modern 

 machine age, for most modern mechanisms are made 

 of combinations of six simple machines. 



Did you ever stop to consider what an important 

 place machines occupy in our everyday life? At every 

 turn we make use of them to save our strength and 

 time. Machines such as food choppers, can openers, 

 and beaters help in the kitchen, while others work for 

 us in the basement and about the house. In offices, 

 besides writing our letters, they perform tasks that 

 are almost human by adding, subtracting, multiplying, 

 and dividing. The automobile and airplane, each of 

 which is a machine built up of simpler ones, take us 



about the country with great speed. 



In this unit we want you to learn more about ma- 

 chines and how they work in order that you may use 

 them more intelligently. 



How many of these things do you already know? 



1. Why are trucks or rollers placed under heavy 

 boxes when they are moved about? 



2. Where does energy come from? 



3. What is energy? 



4. A plank or board is often used as a track to 

 roll heavy objects into a wagon or truck. Explain. 



5. Why is one jerked backward in a car that starts 

 suddenly? 



6. Why do you hold on to something in a car 

 that is going around a turn? 



7. Why does mud fly off the tire of a moving 

 bicycle? 



8. Make a list of all the machines used around your 

 home. 



9. Find as many advertisements of machines in 

 magazines and newspapers as you can. Paste these 

 on a sheet of paper and bring them to class. 



10. Why is it easier to unscrew a nut from a bolt 

 with a long-handled wrench than with your fingers? 



11. Why are ball and roller bearings used in au- 

 tomobiles and other machines? 



12. List as many ways as you can in which fric- 

 tion is made use of in the automobile. 



13. How many ways can you list in which energy 

 is changed from one form into another, as from 

 electricity into light? 



TOPIC 1. SOME FORCES AND MOTIONS IN DAILY LIFE 



SUGGESTED PROBLEMS AND QUESTIONS 



1. Is perpetual motion possible? 



2. What are the advantages and disadvantages 

 of friction? 



3. Why do substances have weight? 



4. Why does one pitch forward in a car that is 

 suddenly stopped, and why are turns on rail- 

 roads and highways banked? 



5. How much distance must be allowed for 

 stopping cars traveling at different speeds? 



SUGGESTIONS AND HELPS FOR STUDY 



1. In the study of this topic try to see how the 

 principles of science you learn apply in your own 

 daily life. Try to secure any experiences suggested 



by the problems which you may not have had, such 

 as observing the "bank" on turns of railroads and 

 highways. 



2. The following words may be new to you. Care- 

 fully study them and after learning their meaning, try 

 to use them frequently so that they may become a 

 part of your vocabulary. 



pvrpetTXtil never ceasing. 



Mrnc&twn the application of liquids or solids to rub- 

 bing surfaces to reduce friction; for example, oil is 

 a lubricant. 



inertia the property possessed by all bodies which 

 causes the body to resist being set in motion, or, 

 once in motion, to resist being stopped. 



force a push or pull exerted on a body. 



centrifugal force a force in a rotating body which pulls 

 awav from the center of rotation. 



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