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Basic Machines and How They Work ( Review )
Our Awards Booktopia's Charities. Are you sure you would like to remove these items from your wishlist? Remove From Wishlist Cancel. Cattle ramps, a mountain highway and the gangplank are familiar examples. By substituting these values in the formula, you get The inclined plane permits you to overcome a large resistance, by applying a small force through a longer distance when raising the load. Here you see the driver easing the pound barrel up to the bed of the truck, 3 feet above the sidewalk.
He is using a plank 9 feet long. With the ramp, he can apply his effort over the entire 9 feet of the plank as he rolls the barrel to a height of 3 feet. It looks as if he could use a force only three-ninths of , or pounds, to do the job. And that is actually the situation. Since the ramp is three times as long as its height, the mechanical advantage is three. You find the theoretical mechanical advantage by dividing the total distance of the effort you exert by the vertical distance the load is raised or lowered. You have probably used wedges. Abe Lincoln used a wedge to help him split logs into rails for fences.
The blades of knives, axes, hatchets, and chisels act as wedges when they are forced into apiece of wood. The wedge is two inclined planes set base-to-base. Remember it from chapter 1? A few sledgehammer blows on a wedge will quickly and firmly tighten up the shoring. Long, slim wedges give high mechanical advantage. For example, the wedge of figure has a mechanical advantage of six. Chipping scale or paint off steel is a tough job.
How-ever, you can make the job easier with a compressed-air chisel. The wedge-shaped cutting edge of the chisel gets in under the scale or the paint and exerts a large amount of pressure to lift the scale or paint layer. The chisel bit is another application of the inclined plane. Going aboard the ship by gangplank illustrated in figure , is easier than climbing a sea ladder.
You appreciate the mechanical advantage of the gangplank even more when you have to carry your seabag or a case of sodas aboard. SUMMARY This chapter covered the following points about the inclined plane and the wedge: The inclined plane is a simple machine that lets you raise or lower heavy objects by applying a small force over a long distance. Remember that hatch dog in figure ? The use of the dog to secure a door takes advantage of the lever principle. If you look sharply, you can see that the dog seats itself on a steel wedge welded to the door.
As the dog slides upward along this wedge, it forces the door tightly shut. This is an inclined plane, with its length about eight times its thickness. That means you get a theoretical mechanical advantage of eight. In chapter 1, you figured that you got a mechanical advantage 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 simple gadget, is it? Push down with 50 pounds heave on the handle and you squeeze the door 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 load up the ramp. The wedge is two inclined planes set base-tobase. It finds its greatest use in cutting or splitting materials. Explain the use of the jack. Discuss the use of the micrometer The screw is a simple machine that has many uses.
The vise on a workbench makes use of the mechanical advantage M. You get the same advantage using glued screw clamps to hold pieces of furniture together, a jack to lift an automobile, or a food processor to grind meat.
As you turn the pencil, the paper is wound up so that its hypotenuse forms a spiral thread. The pitch of the screw and paper is the distance between identical points on the same threads measured along the length of the screw.
A screw is a modification of the inclined plane. Cut a sheet of paper in the shape of a right triangle and you have an inclined plane. Here you see the type of jack screw used to raise a house or apiece of heavy machinery. Notice that the jack has a lever handle; the length of the handle is equal to r.see
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The circumference of this circle is equal to 2x. Remember that n equals 3. That is the distance you must apply the effort of the lever arm. At the same time, the screw has made one revolution, raising its height to equal its pitch y.
You might say that one full thread has come up out of the base. At any rate, the load has risen a distance p. Remember that the theoretical mechanical advantage T. Substituting, Figure The spindle attaches to the thimble and is fitted with screw threads that move the spindle and thimble to the right or left in the sleeve when you rotate the thimble. These screw threads are cut 40 threads to the inch. This represents one of the smallest divisions on the micrometer. To allow even finer measurements, the thimble is divided into 25 equal parts. It is laid out by graduation marks around its rim, as shown in figure If you turn the thimble through 25 of these equal parts, you have made one complete revolution of the screw.
The micrometer in figure reads 0. This tells you that the diameter of this bit is 0. A pound pull on the handle would result in a theoretical lift of 50 x or about 30, pounds—15 tons for 50 pounds. However, jacks have considerable friction loss. The threads are cut so that the force used to overcome friction is greater than the force used to do useful work.
If the threads were not cut this way and no friction were present, the weight of the load would cause the jack to spin right back down to the bottom as soon as you released the handle. It takes a lot of circular motion to get a small amount of straight line motion from the head of the jack. In figure , you see a cutaway view of a micrometer. The thimble turns freely on the sleeve, Figure Because you can make accurate measurements with this instrument, it is vital in every machine shop.
However, you can do it by using a turnbuckle. The turnbuckle fig, is an application of the screw.
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If you turn it in one direction, it takes up the slack in a cable. Turning it the other way allows slack in the cable. Notice that one bolt of the turnbuckle has left-hand threads and the other bolt has right-hand threads.
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Thus, when you turn the turnbuckle to tighten the line, both bolts tighten up. If both bolts were right-hand threadstandard thread-one would tighten while the other one loosened an equal amount. That would result in no change in cable slack. Most turnbuckles have the screw threads cut to provide a large amount of frictional resistance to keep the turnbuckle from unwinding under load.
In some cases, the turnbuckle has a locknut on each of the screws to prevent slipping. Ever wrestled with a length of wire rope? Riggers have dreamed up tools to help subdue wire rope. The crew splices a thimble-a reinforced loop—onto the end of the cable.
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Rotating the handle causes the jaw on Figure This machine is a modification of the vise on a workbench. Notice the right-hand and left-hand screws on the left-hand clamp. Figure shows you another use of the screw.
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Suppose you want to stop a winch with its load suspended in mid-air. To do this, you need a brake.