46a ENGINEERING ON THE FARM 



Correctly speaking, a fork is a tool, a self-binder a machine, 

 and both are implements. 



Force. Force is the action exerted by a body tending to 

 cause a change in the nun ion of another body. When a 

 force causes a change in the state of motion of a body, work 

 is said to be done. The ability to do work is energy and may 

 be classified as potential, or energy of position, and kinetic, 

 or energy of motion. A flowing stream has potential energy ; 

 if a dam is built, power will be developed. The water falling 

 over the dam has kinetic energy owing to its motion, and the 

 water stored up back of the dam has potential energy owing 

 to its position. The sources of farm energy are feed, fuel, 

 wind, and water. The unit of work is the foot-pound, or 

 one pound acting through a distance of one foot (vertical 

 lift). Power is the rate of doing work, the unit being the 

 horse power. The value of a horse power is supposed to 

 have been derived from the average rate of .work done per 

 minute by a horse in hoisting coal in the English mines. It 

 is equivalent to the weight in pounds multiplied by the 

 distance moved vertically in one minute in feet divided by 

 33,000. Horse power is indicated by "h. p." 



Friction. In order that one may perform work with a 

 machine, a certain degree of power must be applied to the 

 machine which in turn performs the work. The power 

 delivered to the work is always less than the power supplied 

 to the machine. The power consumed in the operation of 

 the machine is due to friction. Friction is the resistance 

 which one surface offers to another sliding over it. This 

 sliding takes place in a machine wherever there is motion. 

 The efficiency of the machine is the ratio of the power 

 applied to that delivered to the work. If 20 horse power is 

 applied and only 15 horse power delivered, the efficiency is 

 75 per cent, one-fourth of the power being lost between its 

 application to the machine and delivery to the work. The 

 coefficient of friction is the ratio between the force holding 

 the surfaces together and the force at the plane of contact 



