A practical treatise on the technics and principles of dental orthopedia and prosthetic correction of cleft palate . ay of the blade, the oar becomes a lever of the secondkind and the boat or work moves forward. But if the velocity of the moving poweris not sufficient to overcome the inertia of the boat, the only work that the oar orlever can be said to accomplish is the movement of the yielding water in front of theblade, with fulcrum at the oarlock—or the action of a lever of the firs^ kind. Itcan be seen in this common example of a lever of the second kind that the fulcrum,or so-called poin
A practical treatise on the technics and principles of dental orthopedia and prosthetic correction of cleft palate . ay of the blade, the oar becomes a lever of the secondkind and the boat or work moves forward. But if the velocity of the moving poweris not sufficient to overcome the inertia of the boat, the only work that the oar orlever can be said to accomplish is the movement of the yielding water in front of theblade, with fulcrum at the oarlock—or the action of a lever of the firs^ kind. Itcan be seen in this common example of a lever of the second kind that the fulcrum,or so-called point of resistance, is a broad moving area of water. And it wouldbe none the less a lever if its so-called point of work was also spread over a broadenedarea upon the lever, both areas of fiolcrtim and weight moving and reacting uponeach other. This combination of activities is exactly that which is exemplified in the alveo-lus of a tooth when force is appHed in a lateral direction upon the crown. It isperfectly illustrated also in the following example of the post lever. CHAPTER XIII. PRINCIPLES OF MECHANICS 99. ^^- ^^- Post Lever.—If you should drive a four-foot post one-half its length into clayey soil of uniform quality, and then take holdof the top of the post and move it back and forth with a viewof subsequently pulling it out of the ground, you would beworking a lever which combines the qualities of the first andsecond kinds, or one like the oar in which the so-called areasof fulcrum and weight act as fiolcrums to the other. SeeFig. 35. After pulling the post out of the groiind, if it werepossible for you to make a transverse section of the soil forthe purpose of examining the shape of the hole you hadmade, you would find it somewhat the shape of an hour-glass; the upper portion of the opening being about twice aslarge as the lower.* As the post is forced in one direction the soil in front of it, along its upper sphere of action, will become impacted, or thrust to one s
Size: 1080px × 2315px
Photo credit: © The Reading Room / Alamy / Afripics
License: Licensed
Model Released: No
Keywords: ., bookcentury1900, bookdecade1920, bookidpracticaltre, bookyear1921
