WAGONS, BUGGIES, AND SLEDS 253 



the extra force required to accelerate the load. Springs 

 tend to reduce draft, as they reduce the shocks and con- 

 cussions due to the unevenness and irregularities of the 

 road surface. Their effect is greater at high speeds than 

 at lower. 



359. Grade resistance. Grade resistance involves the 

 principle of the inclined plane, and may be explained as 

 the force required to prevent the load from rolling down 

 the slope. It is independent of everything except the 

 angle of inclination. 



In Fig. 184 if W be the load and P the grade resistance, 

 AB the height of the grade and CB the length, by com- 

 pleting the force diagram similar triangles are obtained, 

 from which it is seen : 



P : AB :: W\ AC, or P = W X 



As AC is very nearly equal to BC for ordinary grades, 

 no great error will be accrued by substituting BC for AC. 

 Grades are usually expressed in the number of feet rise 



and fall in 100 feet, or in 

 the number of per cent the 

 total rise is of the length 

 of the grade. Then for 

 B practical purposes the 

 FIG - l8 4 grade resistance is equal to 



the per cent of the total load, which expresses the grade. 

 For example, if the grade is 5 per cent and the load 

 2,000 pounds, the grade resistance will be 100 pounds. 

 The foregoing analysis does not take into account the 

 way the load is placed on the wagon or angle of hitch, 

 which may lead to error. 



360. Handy wagons. The name handy wagon is given 

 to a low-wheeled, broad-tired wagon used about the farm 

 for hauling implements, grain, and stock. They are used 



