WEBVTT 00:00:00.000 --> 00:00:02.000 Well, we've already learned a lot about electricity. 00:00:02.000 --> 00:00:05.000 We know that negative charges like to be with positive charges. 00:00:05.000 --> 00:00:08.000 We know four methods to charge an object, 00:00:08.000 --> 00:00:12.000 and we've learned that the earth is both a source and a sink for electrons. 00:00:12.000 --> 00:00:14.000 But one thing we haven't talked about at allâ€” 00:00:14.000 --> 00:00:17.000 one of the most important concepts in physics is energy. 00:00:17.000 --> 00:00:20.000 Why don't we go back to Professor Fregonese and see what he has to say 00:00:20.000 --> 00:00:22.000 about energy as it relates to electricity. 00:00:22.000 --> 00:00:27.000 One of the most evident effects of electricity are attractions and repulsions 00:00:27.000 --> 00:00:34.000 of electrified bodies and this is important because you can use these forces 00:00:34.000 --> 00:00:37.000 to produce work, to produce energy. 00:00:37.000 --> 00:00:43.000 We can start understanding it with an analogy with gravity, which is simple 00:00:43.000 --> 00:00:47.000 because we have only attraction and electricity is much more complicated because 00:00:47.000 --> 00:00:50.000 you have also this complication of repulsion. 00:00:50.000 --> 00:00:56.000 If I have a body of mass, there is an attraction between the body and the earth 00:00:56.000 --> 00:00:59.000 and there is potential energy. 00:00:59.000 --> 00:01:04.000 If I drop this body, it has the capacity to produce some work 00:01:04.000 --> 00:01:08.000 maybe to break a neck down there. 00:01:08.000 --> 00:01:12.000 It goes down and the potential energy diminishes 00:01:12.000 --> 00:01:17.000 and it acquires kinetic energy, movement, velocity, 00:01:17.000 --> 00:01:21.000 and which is proportionate to the square of velocity. 00:01:21.000 --> 00:01:27.000 With electricity, it's more complicated because of repulsion but the idea is similar. 00:01:27.000 --> 00:01:32.000 You can use the interactions between electrified borders between charges 00:01:32.000 --> 99:59:59.999 to produce work so to have energy to produce something.