Figure 1-10.-It’s a dog.APPLICATIONS AFLOAT AND ASHOREDoors, called hatches aboard a ship, are locked shutby lugs called dogs. Figure 1-10 shows you how thesedogs are used to secure the door. If the handle is fourtimes as long as the lug, that 50-pound heave of yoursis multiplied to 200 pounds against the slanting face ofthe wedge. Incidentally, take a look at the wedge—it’san inclined plane, and it multiplies the 200-pound forceby about 4. Result: Your 50-pound heave actually endsup as a 800-pound force on each wedge to keep the hatchclosed! The hatch dog is one use of a first-class lever incombination with an inclined plane.The breech of a big gun is closed with a breech plug.Figure 1-11 shows you that this plug has someinterrupted screw threads on it, which fit into similarFigure 1-12.-Using a wrecking bar.interrupted threads in the breech. Turning the plug partway around locks it into the breech. The plug is lockedand unlocked by the operating lever. Notice that theconnecting rod is secured to the operating lever a fewinches from the fulcrum. You’ll see that this is anapplication of a second-class lever.You know that the plug is in there good and tight.But, with a mechanical advantage of 10, your100-pound pull on the handle will twist the plug loosewith a force of a half ton.If you’ve spent any time opening crates at a base,you’ve already used a wrecking bar. The sailor infigure 1-12 is busily engaged in tearing that crate open.Figure 1-11.-The breech of an 8-inch gun.1-6
Integrated Publishing, Inc. - A (SDVOSB) Service Disabled Veteran Owned Small Business