52 APPLIED SCIENCE 



or sharp edge? Does the part away from the cutting edge become 

 thinner or thicker? 



7. Name a number of "run appliances," that is, appliances 

 or tools connecting two floors or stagings at different levels. 



8. Is the "run" appliance always longer than the perpendicu- 

 lar distance between the two levels? 



9. Divide all the ordinary tools and appliances that you remem- 

 ber into the following groups: hitting tools; twisting tools; screw 

 tools; hoisting tools; cutting tools; "run" appliances. 



10. Name a list of simple tools and appliances and state whether 

 "speed" or "power" is gained by the use. 



11. Name some machines that involve more than one of the 

 simple machines or mechanical principles. 



12. What is the meaning of the expression "mechanical effi- 

 ciency "? " Mechanical advantage"? 



13. What is friction? 



14. Where is friction found? 



15. Is friction a form of energy? 



16. Is friction a "necessary evil" or has it some advantage? 



17. Do we use friction in walking? 



18. Is friction used in the case of automobiles? 



19. How is friction reduced? 



20. What are roller bearings? Are they useful in reducing 

 friction? 



21. Why is sand placed on the railway track? 



22. Why are roller bearings placed on skates? 



23. Explain why it is difficult to walk on ice. 



24. What is the object of waxing a floor before dancing? 



25. Give the approximate percentage of efficiency of the different 

 simple machines. 



26. What is a lubricant? 



27. What are some of the dangers of excessive friction among 

 woody materials, paper, or cotton stock? 



Problems 



1. A plank 11 ft. long is used to raise a barrel of flour (196 Ibs.) 

 into a car 3^ ft. high. What force is necessary to raise it? 



