Transportation on Land 263 



mon use in your community, that have been transported at least five 

 hundred miles. 3. How have modern facilities for travel changed 

 the population of your community? 4. What are the greatest geo- 

 graphical obstacles to travel and transportation? 5. What effects 

 have geographical conditions on the civilization -of a people ? 



6. How may the transporting capacity of a man or a horse be in- 

 creased by the use of two poles? 7. If a plank is of uniform dimen- 

 sions and weighs 40 pounds, what force will be required to raise one 

 end? 8. If the plank is 16 feet long and a weight of 300 pounds is 

 placed 2 feet from one end, what force must be used to lift the other? 

 9. Where are the fulcrum, the force arm, and the resistance arm of a 

 nutcracker? Of a pair of pliers? Of a wheelbarrow? Of the drive 

 wheel of a locomotive? 10. If the force is applied ten times as far 

 away from the fulcrum as the resistance, how many times the magni- 

 tude of the force is the magnitude of the resistance? 11. Mention 

 several appliances which are modified forms of the simple lever. 

 12. What advantage did Archimedes claim for the lever? Who 

 was he and for what was he noted? 



13. Mention early uses of the roller and the wheel. 14. What is 

 sliding friction? 15. Mention several instances where friction is 

 necessary. 16. Does sliding friction increase or decrease when slip- 

 ping begins? 17. What practical knowledge of friction does the 

 locomotive engineer or the automobile driver need? 18. Why do 

 car wheels turn and not ordinarily slide on the track? 19. How is 

 friction reduced in a wagon, bicycle, automobile, windmill, and rail- 

 road car? 



SUGGESTIVE QUESTIONS 



1. Is starting friction greater than sliding friction? 2. What does 

 the experiment with the block and spring balance show as to this? 

 3. Does sliding friction decrease with increase of rate of movement? 

 Does the spring balance show greater or less force when pulling the 

 block slowly or when pulling it rapidly? 4. If the sliding surfaces 

 of block and track were lubricated, would the friction decrease ? Why? 

 What other means might be employed to reduce friction? 5. Do you 

 know why a motorman or engineer on a steam locomotive always 

 reduces the air pressure on brakes when the car or train is just about 

 stopping? 6. Name some of the uses of friction as shown in the com- 

 mon utilities of the home. Of the shop. Why do nails that are well 

 driven hold securely ? How should tent stakes slant, toward or away 

 from the tent? Why? Why are engines able to start on an appar- 

 ently smooth track? 7. What is the principal advantage of rollers, 

 balls, or wheels, over sliding? 



