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 dynamic, energy.

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. 9