energy into matter can occur only under very
Look at the lever in figure 4-12. You see the
special conditions, which we need not consider
pivotal point F (fulcrum); the effort (E), which
now. All the energy transformations that we will
you apply at a distance (A) from the fulcrum; and
deal with can be understood quite simply if we
a resistance (R), which acts at a distance (a) from
consider only the principle of the conservation of
the fulcrum. Distances A and a are the lever arms.
energy-that is, ENERGY IN MUST EQUAL
Figure 4-13 shows the three classes of levers. The
ENERGY OUT.
location of the fulcrum (the fixed or pivot point)
with relation to the resistance (or weight) and the
TRANSFORMING HEAT TO WORK.--
effort determines the lever class.
The energy transformation of primary interest
in the shipboard gas turbine plant is the
transformation from heat to work. To see how
FIRST-CLASS LEVERS
this transformation occurs, we need to consider
the pressure, temperature, and volume relation-
In the first-class lever (fig. 4-13, view A), the
ships which hold true for gases. These relation-
fulcrum is located between the effort and the
ships may be summarized as follows:
resistance. As mentioned earlier, the seesaw is a
good example of the first-class lever. The amount
When the temperature is held constant,
of weight and the distance from the fulcrum can
increasing the pressure on a gas causes a pro-
be varied to suit the need. Another good example
portional decrease in volume. Decreasing the
is the oars in a rowboat. Notice that the sailor in
pressure causes a proportional increase in
volume.
When the pressure is held constant,
increasing the temperature of a gas causes a pro-
portional increase in volume. Decreasing the
temperature causes a proportional decrease in
volume.
When the volume is held constant,
increasing the temperature of a gas causes a
proportional increase in pressure. Decreasing the
temperature causes a proportional decrease in
Figure 4-12.--A simple lever.
pressure.
LEVERS/LEVERAGE
The LEVER is one of the six types of simple
machines. The others are the BLOCK, the
WHEEL AND AXLE, the INCLINED PLANE,
the SCREW, and the GEAR. Physicists recognize
only two basic "principles" in machines; namely,
the lever and the inclined plane. The block, the
wheel and axle, and the gear may be considered
levers. The wedge and the screw use the principle
of the inclined plane. In this section we will discuss
levers and leverage only.
The simplest machine, and perhaps the one
with which you are most familiar, is the LEVER.
A seesaw is a familiar example of a lever in which
one weight balances the other. There are three
basic parts which you will find in all levers;
namely, the FULCRUM, a force or EFFORT,
and a RESISTANCE. The mechanical advantage
gained by using a lever is called LEVERAGE.
Figure 4-13.--Three classes of levers.
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