Title: Farm implements, and the principles of their construction and use; an elementary and familiar treatise on mechanics, and on natural philosophy generally, as applied to the ordinary practices of agriculture ..
Year: 1854 (1850s)
Authors: Thomas, John Jacob, 1810-1895. [from old catalog]
Subjects: Agricultural implements
Publisher: New York, Harper and Brothers
Contributing Library: The Library of Congress
Digitizing Sponsor: The Library of Congress
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Text Appearing Before Image:
as four is to three,then the weaker horse should be attached to the armof the whipple-tree made as much longer than the oth-er arm as four is to three. In all the preceding estimates, the influence of theweight of the lever has not been taken into consider-ation. In a lever of the first kind, if the thickness ofthe two arms he so adjusted that it will remain bal-anced on the fulcrum, its weight will have no othereffect than to increase the pressure on the fulcrum;but if it be of equal size throughout, its longer arm,being the heaviest, will add to its power. The amountthus added will be equal to the excess in the weightof this arm, applied so far along as the centre of grav-ity of this excess. If, for example, a piece of scantling twelve feet long,a b, Fig: 49, beused as a lever tolift the corner ofa building, thenthe two portions, a c, c d, will mutually balance eachother. If these be each a foot in length, the weight often feet will be left to bear down the lever. The cen- Fig. 49.
Text Appearing After Image:
70 MECHANICS. tre of gravity of this portion will be at e, six feet fromthe fulcrum,and it will consequently exert a force un-der the building equal to six times its own weight.If the scantling weigh five pounds to the foot, or fiftypounds for the excess, this force will be equal to threehundred pounds. In the lever of the second kind, its weight operatesagainst the moving power. If it be of equal sizethroughout, this will be equal to just one half theweight of the lever, the other half being supported bythe fulcrum. With the lever of the third kind, the rule applied tothe first must be exactly reversed. COMBINATION OF LEVERS. A great power may be attained without the incon-venience of resorting to a very long lever, by means ofFi 50 a combination of levers. i ; n, $ In Fig. 50, the small &• i #\ ; ffiJk weight P, acting as a r r W • , movmg power, exerts athree-fold force on the next lever; this, in its turn, actsin the same degree on the third, which again increasesthe power
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