66 MOTION AND FORCE 



fixed so as to turn with it may serve, or one can easily be made. 

 An old clock will furnish gear wheels. An inclined plane can 

 be made wherever convenient, and a thick knife blade will do 

 for a wedge. 



QUESTIONS 



1. Define work. How is work measured ? What is the unit 

 of work ? 



2. What is meant by power ? What is the unit of the rate of 

 doing work ? How much is one foot pound ? one horse power ? 



3. What is a machine? Can a machine do work of itself? 

 Does a machine gain or lose work ? 



4. What, in general, is the use of machines to man ? Name 

 four special uses of them. Illustrate each. 



5. State the Law of Machines. Show how a lever applies this 

 law. Is a movable pulley used to gain force or speed ? 



6. Why do tailors' shears have long blades and short handles, 

 while plumbers' shears have short blades and long handles ? 



7. Why does a bicycle of high gear run harder than one of 

 low gear? 



8. What is the advantage gained in using: a single pulley? 

 a windmill? a coiled spring in a watch? the walking beam on an 

 engine? a wheel and axle? 



9. State the advantage given by a second-class lever and by 

 a third-class lever. What can you say of the advantage in levers 

 of the first class ? 



10. Name as many examples of levers in use as you can. 

 Name some familiar uses of the screw and the wedge. 



11. Explain the use of gear wheels in machinery. 



