Figure 4-2.-A wedge.driving the wedge full-length into the material tocut or split, you force the material apart a distanceequal to the width of the broad end of the wedge.See figure 4-2.Long, slim wedges give high mechanical advan-tage. For example, the wedge of figure 4-2 has amechanical advantage of six. The greatest value ofthe wedge is that you can use it in situations inwhich other simple machines won’t work. Imaginethe trouble you’d have trying to pull a log apartwith a system of pulleys.APPLICATIONS AFLOAT AND ASHOREA common use of the inclined plane in the Navyis the gangplank. Going aboard the ship bygangplank illustrated in figure 4-3, is easier thanclimbing a sea ladder. You appreciate themechanical advantage of the gangplank even morewhen you have to carry your seabag or a case ofsodas aboard.Remember that hatch dog in figure 1-10? Theuse of the dog to secure a door takes advantage ofthe lever principle. If you look sharply, you cansee that the dog seats itself on a steel wedgewelded to the door. As the dog slides upward alongthis wedge, it forces the door tightly shut. This isan inclined plane, with its length about eighttimes its thickness. That means you get atheoretical mechanical advantage of eight. Inchapter 1, you figured that you got a mechanicaladvantage of four from the lever action of the dog.The overall mechanical advantage is 8 x 4, or 32,neglecting friction. Not bad for such a simplegadget, is it? Push down with 50 pounds heave onthe handle and you squeeze the doorFigure 4-3.—The gangplank is an inclined plane.shut with a force of 1,600 pounds on that dog.You’ll find the damage-control parties usingwedges by the dozen to shore up bulkheads anddecks. A few sledgehammer blows on a wedge willquickly and firmly tighten up the shoring.Chipping scale or paint off steel is a tough job.How-ever, you can make the job easier with acompressed-air chisel. The wedge-shaped cuttingedge of the chisel gets in under the scale or thepaint and exerts a large amount of pressure to liftthe scale or paint layer. The chisel bit is anotherapplication of the inclined plane.SUMMARYThis chapter covered the following points aboutthe inclined plane and the wedge:The inclined plane is a simple machine that letsyou raise or lower heavy objects by applying a small force over a long distance.You find the theoretical mechanical advantage of the inclined plane by dividing the length of the ramp by the perpendicular height of the load that is raised or lowered. The actual mechanical advantage is equal to the weight of the resistance or load, divided by the force that must be used to move the loadup the ramp.The wedge is two inclined planes set base-to-base. It finds its greatest use in cutting or splitting materials.4-2
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