Also, whenever an electric motor is run or electrical
energy is transmitted a loss occurs in the wire leads, which is called a
"resistance loss." Therefore it is necessary to use wire large enough
to prevent high losses and excessive heating. In the case of an electric flat
iron or other heating device, the transformation of electrical energy to heat
energy is not considered a loss because it is produced for a useful purpose.
(d) Chemical Energy The chemical energy
which a substance has is contained in it by virtue of its chemical composition.
It is rather difficult to understand what chemical composition has to do with
work, but it is easy to understand that chemical energy can be converted into
work. Such a conversion takes place in a gasoline, oil, or steam engine when
the chemical energy of its fuel is converted into work for driving automobiles,
motor boats, ships, etc.
(e) Mechanical Energy. There
are two kinds of mechanical energy potential energy and kinetic, or
Potential energy exists
by virtue of the position or condition of matter. An example of potential
energy stored in matter by virtue of its position is a mass elevated to a
position from which it can do work when lowered, such as a reservoir of water
at an elevated position, which can be made to turn water wheels at a lower
elevation for driving machinery. An example of potential energy by virtue of
condition is a compressed gas which can be made to perform work when released,
or a rarefied gas (vacuum or partial vacuum) which can also be made to do work.
A common example of this is the windshield wiper of an automobile where the wiper
motor is worked from the vacuum tank.
Dynamic energy exists
in moving bodies. It requires work to set a mass of matter in motion and
likewise to stop it once it is set in motion. An example of kinetic energy is
water flowing in a pipe. If we consider again an elevated reservoir supplying
water to a water wheel, we will remember that the energy of the water when it
was in the reservoir was potential energy. The water is piped to the water
wheel, and at a point just before it comes in contact with the wheel it has no
longer any potential energy, although its energy has not yet been used in
turning the wheel; but the potential energy which was in the water in the
reservoir has been converted to dynamic energy or energy of motion.
In order to obtain a clearer understanding of the
difference between potential and kinetic energy, let us for a moment consider
the two principal types of old time water wheels used by the miller in grinding
flour. One type of wheel the "overshot" wheel contained a
row of boxes, or "buckets," around the rim of the wheel. The axis of
the wheel was horizontal, and the location of the wheel was so chosen that
water from a higher elevation could be directed by means of a trough so as to
fall into the buckets at the top of one side of it. The weight of the water in
these buckets caused the wheel to turn. In this case the energy to rotate the
wheel arose directly out of the potential energy stored up in the water by
virtue of its elevation.
On the other hand, we may consider the operation of an
"undershot" wheel. This type of wheel was similar in its location and
mounting to that of the "overshot" wheel described in the previous
paragraph, but, instead of "buckets," a number of "paddles"
were located around the rim of the wheel, and, instead of water being directed
over the wheel, it was caused to flow under the wheel is such a way as to
strike the paddles. The kinetic energy of the swiftly moving water, upon being
brought to bear against the paddles, rotated the wheel.
(f) Sound Energy. Sound is not usually considered as a separate form of energy but as a
variety of mechanical energy. You will remember that under "Mechanical
Energy" it was stated that both compressed gases and rarefied gases
contained energy by virtue of their condition, and we stated that this energy
could be converted into work. Sound, being an alternate succession of
compression and rarefactions of air, is a particular form of energy which is
capable of doing work, such as driving the membrane of the ear to produce the sensation
of hearing, or driving the diaphragm of a microphone to produce electrical
impulses. Likewise, sound waves drive the diaphragm of an Ediphone machine,
which, in turn, drives the cutting point that makes a record on a wax cylinder.
This is similar to the method used in making the old type of phonograph
records. In the new method the sound is picked up with a microphone and
converted into electrical impulses which are amplified before being converted
to mechanical impulses for cutting the record.
Copyright 1930 RCA Photophone, Inc.