Practical talks on farm engineering : A simple explanation of many everyday problems in farm engineering and farm mechanics written in a readable style for the practical farmer . roduct of the force in pounds and the distancein feet. The unit used is the foot-pound. If, then,the iron above mentioned weighs ten poundsthe work done when it falls two feet is theproduct of ten and two, that is, twenty foot-pounds. Work is the product of force anddistance. Energy is the ability to do work. It is thecapacity for work that a body or substance has,and is measured in foot-pounds just the sameas work. T
Practical talks on farm engineering : A simple explanation of many everyday problems in farm engineering and farm mechanics written in a readable style for the practical farmer . roduct of the force in pounds and the distancein feet. The unit used is the foot-pound. If, then,the iron above mentioned weighs ten poundsthe work done when it falls two feet is theproduct of ten and two, that is, twenty foot-pounds. Work is the product of force anddistance. Energy is the ability to do work. It is thecapacity for work that a body or substance has,and is measured in foot-pounds just the sameas work. The weight mentioned, before it fell,had the ability to fall and do twenty foot-pounds of work. Thus we say that it pos-sessed twenty foot-pounds of energy. Power is the rate of doing work. If anengine can do 33,000 foot-pounds of work in oneminute, it is a one-horsepower engine, thatfigure being the standard chosen to represent ahorsepower. Power has to do with time. Anyengine can do 33,000 foot-pounds of work,even a toy engine if you give it time enough. HORSEPOWER OF AN ENGINE 121 The point to be noticed is that a one-horse-power engine must be able to do that much work. Fig. 26.—The engine indicator in one minute. A two-horsepower engine mustdo that amount in half a minute, or, what is 122 FARM ENGINEERING the same thing, it must do twice that amountin one minute. To measure the indicated horsepower of asteam or oil engine, an instrument known asthe indicator is used. The illustration showsthe general appearance of the indicator usedwith steam engines, and the same generalarrangement is found in all indicators. Thereis a cylinder to which steam is admitted fromthe engine cylinder. The steam forces thepiston back against the resistance of a coiledspring which has been experimented with previ-ously, so that the pressure exerted by the steamon the little piston is known from the amountthe spring is compressed. As the area of thesmall piston is usually just one square inch, th
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