. Elementary lessons in the physics of agriculture. Agricultural physics. [from old catalog]. 40 sented at A, Fig. 19, a load acting at W puts the upper edge under a stretching We know from experience that in case the board breaks under its load when so situated the fracture will occur somewhere near 5-6. Now in order that this may take place, there must be, with white pine, according to 69, a tensile stress at the upper edge of ten thousand pounds to the square inch, and if the board is one inch thick the upper inch should resist a stress of ten thousand pounds at any point from 5 to
. Elementary lessons in the physics of agriculture. Agricultural physics. [from old catalog]. 40 sented at A, Fig. 19, a load acting at W puts the upper edge under a stretching We know from experience that in case the board breaks under its load when so situated the fracture will occur somewhere near 5-6. Now in order that this may take place, there must be, with white pine, according to 69, a tensile stress at the upper edge of ten thousand pounds to the square inch, and if the board is one inch thick the upper inch should resist a stress of ten thousand pounds at any point from 5 to 1; but we know that no such load will be carried at W. The reason for this, and also for its breaking at 5 rather than at any other point, is found in the fact that the load acts ujoon a lever arm whose length is the distance from the point of attachment of the load to the breaking point, wherever that may be, and this being true the greatest stress comes necessarily at 5. If the board in question is 48 inches long and 6 inches wide, it will, in breaking, tend to revolve about the cen- ter of the line 5-6, and the upper three inches will be put under the longitudinal strain, but according to 69, is ca- pable of withstanding 3 X 10,000 lbs. = 30,000 lbs. without breaking; but in carrying the load at the end, as shown, this cohesive power is acting at the short end of a bent lever whose mean length of power-arm is one-half of 4-5 or inches, while the weight arm is forty-eight inches in length. It should, therefore, only be able to hold at W. pounds; for asP. xP. A. = W. X W. A., we have, 3,000 x = W. x 48, whence W. = ili^« = 937,5 lbs. 48 When a board, in every respect like the one in A, Fig. 19, is placed under the conditions represented in either B. Please note that these images are extracted from scanned page images that may have been digitally enhanced for readability - coloration and appearance of these illustrations may not perfectly resemble the original w
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