Basic Machines

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U.S. Government Printing Office, 1946 - Machinery - 183 pages
 

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Page 74 - Magnifying Force with Gears Gear trains are used to increase the mechanical advantage. In fact, wherever there is a speed reduction, the effect of the effort you apply is multiplied. Look at the cable winch in Figure 24. The crank arm is 30 inches long, and the drum on which the cable is wound has a 15-inch radius. The small pinion gear turned by the crank has 10 teeth, which mesh with the 60 teeth on the internal spur gear. You will find it easier to figure the mechanical advantage of this machine...
Page 84 - You can't make this weight any smaller by the use of any machine. However, if you use the eight-foot plank as shown, you can do that amount of work, by applying a smaller force through a longer distance. Notice that you have a mechanical advantage of 3, so that a 100-pound push down on the end of the plank will raise the 300-pound crate. How long of a distance will you have to exert that 100pound push? Neglecting friction — and in this case you can safely do so — the work done on the machine...
Page 49 - t use the ramp at all, he 'd have to apply a 300-pound force straight up through the three-foot distance. With the ramp, however, he can apply his effort over the entire nine feet of the plank as the barrel is slowly rolled up to a height of three feet. It looks, then, as if he could use a force...
Page 106 - ... Forces You Ve had a lot of experience in measuring forces. You can estimate or "guess " the weight of a package you 're going to mail by "hefting " it. Or you can put it on a scale to find its exact weight. Weight is a common term that tells you how much force or pull gravity is exerting on the object. You can readily measure force with a spring scale. An Englishman named Hooke discovered that if you hang a 1 -pound weight on a spring, the spring stretches a certain distance. A 2-pound weight...
Page 22 - ... diameter of the sheave, or pulley. The resistance, R, acts downward on the arm, FR, which is the radius of the sheave. Since the diameter is twice the radius, the mechanical advantage is two. But, when the effort at E moves up two feet, the load at R is raised only about one foot.
Page 65 - SLEEVE. THIMBLE 40 THREADS TO THE INCH FRAME Gears Did you ever take a clock apart to see what made it tick? Of course you came out with some parts left over when you got it back together again. And they probably included a few gear wheels. Gears are used in many machines. Frequently the gears are hidden from view in a protective case filled with grease or oil, and you may not see them. An eggbeater gives you a simple demonstration of the three things that gears do. They can change the direction...
Page 66 - ... by the arrow. Notice that as B turns in a clockwise direction, its teeth mesh with those of wheel C and cause wheel C to revolve in the opposite direction. The rotation of the crank handle has been transmitted by gears to the beater blades, which also rotate.
Page 111 - snake, " the metal tube tends to straighten out when the pressure inside it is increased. As the tube straightens, the pointer is made to move around the dial. The pressure, in psi, may be read directly on the dial. Air pressure and pressures of steam and other gases and fluid pressures in hydraulic systems are generally measured in pounds per square inch.
Page 90 - ... oiling and greasing bearings and honing and smoothing rubbing surfaces. Wherever you apply force to cause motion, friction makes the actual mechanical advantage fall short of the theoretical mechanical advantage. Because of friction, you have to make a greater effort to overcome the resistance that you want to move. If you place a marble and a lump of sugar on a table and give each an equal push, the marble will move farther. This is because rolling friction is always less than sliding friction....
Page 58 - A 50-pound pull on the handle would result in a theoretical lift of 50 x 603 or 30, 150 pounds. More than fifteen tons for fifty pounds. But 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, if no friction were present, the weight of the load would cause the jack to spin right back down to the bottom as soon as the handle is released. The Micrometer In using...

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