Transportation on Land 279 



road. 4. (a) What motive forces have been employed in land trans- 

 portation ? (6) In what way are they dependent on roads ? 5. Com- 

 pare the loads that can be pulled by a horse on soft roads, hard roads, 

 and steel rails. 



6. Give instances of the modern tendency of railroads to shorten 

 routes. 7. Why are tunnels necessary? Mention several well- 

 known tunnels. 8. (a) Why are there grades on highways ? (6) What 

 determines the steepness of the grade? 9. (a) Compare the force 

 required to move a weight up an incline and to lift it directly. (6) Com- 

 pare the total work done in each case, (c) What is the advantage of 

 the incline? 10. What necessary relation between grades and dis- 

 tances is considered in building a railroad to cross a certain elevation? 



11. (a) What conditions determine the size and power of loco- 

 motives? (6) Can these conditions be easily modified? 12. A 

 train may be how many times the weight of a locomotive which is 

 capable of pulling it? 13. (a) The tractive effort of an engine is what 

 part of its weight? (6) What is rolling friction? (c) How is it re- 

 duced on railroads ? (d) on highways? 



14. Why are not all roads straight? 15. Give examples from ex- 

 perience of the tendency of moving bodies to go in a straight line. 

 16. Explain how an automobilist may " loop the loop." 17. (a) Does 

 a body tend to move straight away from the center of a curve or tan- 

 gent to it ? (6) How can this be demonstrated ? 18. (a) What 

 property of a body is referred to by the term inertia? (6) What 

 instances illustrating this property of bodies have you observed? 

 19. State Newton's Law of Inertia. 20. Why are running courses 

 in a gymnasium usually elevated on the outside? 21. What force 

 is used to balance the inertia in a train which is taking a curve? 

 How? 



SUGGESTIVE QUESTIONS 



1. Why are grades necessary in roads? What means are some- 

 times used to keep a low per cent grade? 2. What is the relation of 

 grades to motive power? 3 How high would 'you have to raise one 

 end of a level plank which is 10 feet long in order to give a grade of 

 2 per cent? 10 per cent? 



4. What is the grade of some portion of the street or road near the 

 school, as determined by means of the instrument described on page 

 277? 



5. Determine the height of a hill by the same instrument, and the 

 grade of a road leading to its summit. 



6. Cogwheel railroads are sometimes used on very steep mountains, 



