CHAPTER XXIV 

 MOTIVE POWER 



The motive power for farm work was originally man 

 himself; then animals of various breeds were trained to 

 supply the simpler forms of energy. The horse, being the 

 best adapted by nature for tractive purposes, has super- 

 seded all other animal power and become the accepted 

 standard of farm power. 



The wide application of certain forces of nature in com- 

 bination with mechanical applicances for the production of 

 power in the industries has led to the development of mechani- 

 cal equipment that under given conditions may be used 

 to replace difficult and laborious operations on the farm. 



THE H,ORSE 



Pulling power of the horse. A horse pulls by means of 

 his weight, his muscles supporting the body and moving 

 it through space. It is considered that he can exert a pull 

 equal to one-tenth of his weight when moving at a rate of 

 2)4 miles per hour throughout the working day. The 

 physical condition of the horse, his age, the weather, and 

 the footing, all tend to decrease or increase his actual pull. 

 For a short period he can exert one-half of his weight and 

 in standing may be able to exert three-fourths of it on a load. 

 However, such exertion can last for only a short period. 

 The force exerted by a horse does not necessarily mean the 

 load he can pull, as the load is dependent upon a number 

 of conditions as discussed in the chapter on roads, but it 

 indicates the force that he can apply to the load. If a 

 strong spring balance were placed between the horse and 

 the load, a 1,000-pound horse, if exerting one-tenth of his 

 weight, would register a pull of 100 pounds on the balance. 

 While there can be no definite amount given for the force 



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