(E) Repeat the experiment in a dark room.
(F) Thoroughly electrify E S, and see if it will cling to the wall strongly enough to support its own weight.
102. Discussion; Electrified and Neutral Bodies. The ebonite sheet became electrified or charged; and as the electrification was produced by friction, we may say that the action of the ebonite indicated the presence of frictional electricity. No one can tell just why the ebonite acted so queerly, but we can learn a great deal by experimenting. Bodies which are not charged are said to be neutral. The table, chairs, earth, etc., are neutral. We may consider that a neutral body has been discharged.
103. Force; Resistance; Work; Potential Energy; Electrification. It takes force to raise water into a tank placed on the roof. In raising the water, work has to be done, and we have to do the work; but when we once have the water in the tank we have accomplished something. The water has potential energy; that is, on account of its high position, we can make it do some work by simply turning a stop-cock so that the water can run out and turn a water-wheel, for example.
It takes force to vigorously rub a piece of ebonite with a flannel cloth, for resistance has to be overcome; that is, work has to be done. Several things are accomplished by this work; heat is produced, for we can feel that the ebonite gets warm; we can hear sounds and see sparks. The simple muscular exertion on our part has been changed to heat, light, and sound. The most wonderful part of it all, however, is that we have electrified or charged the ebonite. We did the work at first, and now the ebonite has the power to do something, as you will[41] soon see. Electrification is, then, a sort of potential energy.
104. Heat and Electrification. We say that heat passes to or from a body to make it hot or cold. Heat produces the sensation of warmth, but heat isn't warmth. We can force a cold body to become hot; in other words, we can get it into a hot condition in various ways, such as rubbing it, hammering it, or by placing it near or in contact with another hot body.
Electrification is, also, a condition or state into which we can force a body; but electrification isn't electricity. We know whether a body is hot or cold by its effects upon us, upon thermometers, and upon other bodies. We can tell, also, whether a body is electrified or not by the way it acts, and, in certain cases, by the sound, heat, and light which accompany the electrification.
Do not get the idea that an electrified body is covered with a layer of electricity just as a board is covered with a layer of paint.
