CHAPTER 1 LEVERS CHAPTER  LEARNING  OBJECTIVES Upon completion of this chapter, you should be able to do the following: l  Explain  the  use  of  levers  when  operating  machines  afloat  and  ashore. l Discuss the classes of levers. Through  the  ages,  ships  have  evolved  from  crude rafts to the huge complex cruisers and carriers of today’s Navy. It was a long step from oars to sails, another long step from sails to steam, and another long step to today’s nuclear power. Each step in the progress of shipbuilding has involved the use of more and more machines. Today’s  Navy  personnel  are  specialists  in  operating and   maintaining   machinery.   Boatswains   operate winches to hoist cargo and the anchor; personnel in the engine room operate pumps, valves, generators, and other machines to produce and control the ship’s power; personnel in the weapons department operate shell hoists and rammers and elevate and train the guns and missile launchers; the cooks operate mixers and can openers; personnel in the CB ratings drive trucks and operate  cranes,  graders,  and  bulldozers.  In  fact,  every rating in the Navy uses machinery sometime during the day’s work. Each  machine  used  aboard  ship  has  made  the physical  work  load  of  the  crew  lighter;  you  don’t  walk the capstan to raise the anchor, or heave on a line to sling cargo aboard. Machines are your friends. They have taken much of the backache and drudgery out of a sailor’s   lift.   Reading   this   book   should   help   you recognize and understand the operation of many of the machines you see about you. WHAT IS A MACHINE? As you look about you, you probably see half a dozen  machines  that  you  don’t  recognize  as  such. Ordinarily  you  think  of  a  machine  as  a  complex device-a  gasoline  engine  or  a  typewriter.  They  are machines; but so are a hammer, a screwdriver, a ship’s wheel. A machine is any device that helps you to do work. It may help by changing the amount of force or the speed of action. A claw hammer, for example, is a machine. You can use it to apply a large force for pulling out a nail; a relatively small pull on the handle produces a much greater force at the claws. We use machines to transform energy. For example, a generator transforms mechanical energy into electrical energy. We use machines to  transfer  energy  from  one place to another. For example, the connecting rods, crankshaft, drive shaft, and rear axle of an automobile transfer energy from the engine to the rear wheels. Another use of machines is to multiply force. We use a system of pulleys (a chain hoist, for example) to lift a heavy load. The pulley system enables us to raise the load by exerting a force that is smaller than the weight of the load. We must exert this force over a greater distance than the height through which the load is raised; thus, the load will move slower than the chain on 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. The best example of this is the bicycle, by which we gain speed  by  exerting  a  greater  force. Machines are also used to change the direction of a force. For example, the Signalman’s halyard enables one end of the line to exert an upward force on a signal flag while a downward force is exerted on the other end. There are only six simple machines: the lever, the block, the wheel and axle, the inclined plane, the screw, and  the  gear.  Physicists,  however,  recognize  only  two basic principles in machines: those of the lever and the inclined  plane.  The  wheel  and  axle,  block  and  tackle, and gears may be considered levers. The wedge and the screw use the principle of the inclined plane. When you are familiar with the principles of these simple  machines,  you  can  readily  understand  the 1-1