Figure 4-2.-A wedge.
driving the wedge full-length into the material to
cut or split, you force the material apart a distance
equal to the width of the broad end of the wedge.
See figure 4-2.
Long, slim wedges give high mechanical advan-
tage. For example, the wedge of figure 4-2 has a
mechanical advantage of six. The greatest value of
the wedge is that you can use it in situations in
which other simple machines wont work. Imagine
the trouble youd have trying to pull a log apart
with a system of pulleys.
APPLICATIONS AFLOAT AND ASHORE
A common use of the inclined plane in the Navy
is the gangplank. Going aboard the ship by
gangplank illustrated in figure 4-3, is easier than
climbing a sea ladder. You
mechanical advantage of the gangplank even more
when you have to carry your seabag or a case of
Remember that hatch dog in figure 1-10? 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
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
Figure 4-3.The gangplank is an inclined plane.
shut with a force of 1,600 pounds on that dog.
Youll find the damage-control parties using
wedges by the dozen to shore up bulkheads and
decks. A few sledgehammer blows on a wedge will
quickly and firmly tighten up the shoring.
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.
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.
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-to-
base. It finds its greatest use in cutting or