CHAPTER 1LEVERSCHAPTER LEARNING OBJECTIVESUpon completion of this chapter, you should be able to do the following:lExplain the use of levers when operating machines afloat and ashore.lDiscuss the classes of levers.Through the ages, ships have evolved from cruderafts to the huge complex cruisers and carriers of today’sNavy. It was a long step from oars to sails, another longstep from sails to steam, and another long step to today’snuclear power. Each step in the progress of shipbuildinghas involved the use of more and more machines.Today’s Navy personnel are specialists in operatingand maintaining machinery. Boatswains operatewinches to hoist cargo and the anchor; personnel in theengine room operate pumps, valves, generators, andother machines to produce and control the ship’s power;personnel in the weapons department operate shellhoists and rammers and elevate and train the guns andmissile launchers; the cooks operate mixers and canopeners; personnel in the CB ratings drive trucks andoperate cranes, graders, and bulldozers. In fact, everyrating in the Navy uses machinery sometime during theday’s work.Each machine used aboard ship has made thephysical work load of the crew lighter; you don’t walkthe capstan to raise the anchor, or heave on a line to slingcargo aboard. Machines are your friends. They havetaken much of the backache and drudgery out of asailor’s lift. Reading this book should help yourecognize and understand the operation of many of themachines you see about you.WHAT IS A MACHINE?As you look about you, you probably see half adozen machines that you don’t recognize as such.Ordinarily you think of a machine as a complexdevice-a gasoline engine or a typewriter. They aremachines; but so are a hammer, a screwdriver, a ship’swheel. A machine is any device that helps you to dowork. It may help by changing the amount of force orthe speed of action. A claw hammer, for example, is amachine. You can use it to apply a large force for pullingout a nail; a relatively small pull on the handle producesa much greater force at the claws.We use machines to transform energy. For example,a generator transforms mechanical energy into electricalenergy. We use machines to transfer energy from oneplace to another. For example, the connecting rods,crankshaft, drive shaft, and rear axle of an automobiletransfer energy from the engine to the rear wheels.Another use of machines is to multiply force. Weuse a system of pulleys (a chain hoist, for example) tolift a heavy load. The pulley system enables us to raisethe load by exerting a force that is smaller than theweight of the load. We must exert this force over agreater distance than the height through which the loadis raised; thus, the load will move slower than the chainon which we pull. The machine enables us to gain force,but only at the expense of speed.Machines may also be used to multiply speed. Thebest example of this is the bicycle, by which we gainspeed by exerting a greater force.Machines are also used to change the direction of aforce. For example, the Signalman’s halyard enablesone end of the line to exert an upward force on a signalflag while a downward force is exerted on the other end.There are only six simple machines: the lever, theblock, the wheel and axle, the inclined plane, the screw,and the gear. Physicists, however, recognize only twobasic principles in machines: those of the lever and theinclined plane. The wheel and axle, block and tackle,and gears may be considered levers. The wedge and thescrew use the principle of the inclined plane.When you are familiar with the principles of thesesimple machines, you can readily understand the1-1
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