1 00:00:00,000 --> 00:00:05,200 So, Dr. D, P.J. tells us that your train set's pretty cool and that you're having problems with it. 2 00:00:05,200 --> 00:00:06,800 Have you figured out what was wrong yet? 3 00:00:06,800 --> 00:00:12,200 Not yet, but I'll bet if we work together as a group and check out the variables one at a time, we'll find the problem. 4 00:00:12,200 --> 00:00:13,200 Okay. 5 00:00:13,200 --> 00:00:14,200 What's a variable? 6 00:00:14,200 --> 00:00:19,200 A variable is one specific thing that can affect or change the end result or the answer. 7 00:00:19,200 --> 00:00:25,200 I've got an idea. I bet it's the wall outlet. There's no electricity there. Nothing else will work. 8 00:00:25,200 --> 00:00:29,200 Let's make that our first variable. How can we check out the wall outlet? 9 00:00:29,400 --> 00:00:31,400 We can plug in something that we know works. 10 00:00:31,400 --> 00:00:34,400 Exactly right. I've got a plasma ball we can use. 11 00:00:34,400 --> 00:00:39,400 Let's turn the lights down a little so we can see it better, and we'll plug it in over there to make sure that it's working. 12 00:00:42,400 --> 00:00:43,400 Cool! 13 00:00:43,400 --> 00:00:46,400 Now let's plug it into the same outlet the train setup uses. 14 00:00:48,400 --> 00:00:51,400 It works fine. I guess we've eliminated one possible variable. 15 00:00:52,400 --> 00:00:54,400 I'll check out a couple of other things later. 16 00:00:54,400 --> 00:00:57,400 By the way, how are you coming along with your electricity mystery? 17 00:00:57,600 --> 00:01:01,600 Well, we still think lightning caused the power outage across the street from the treehouse. 18 00:01:01,600 --> 00:01:06,600 We know that lightning doesn't cause electricity, but we're still not sure where it comes from. 19 00:01:07,600 --> 00:01:08,600 Can you tell us? 20 00:01:08,600 --> 00:01:12,600 Well, electricity is electric charges flowing through the wires of a circuit. 21 00:01:12,600 --> 00:01:14,600 In a standard circuit, the charges are electrons. 22 00:01:14,600 --> 00:01:17,600 There are several ways to force the charges to flow. 23 00:01:17,600 --> 00:01:18,600 Do you know what some of them are? 24 00:01:19,600 --> 00:01:21,600 Don't batteries produce electricity? 25 00:01:21,600 --> 00:01:22,600 That's right. 26 00:01:22,600 --> 00:01:25,600 In fact, we can make our own battery out of lemons or other pieces of fruit. 27 00:01:25,800 --> 00:01:27,800 A battery? From fruit? 28 00:01:27,800 --> 00:01:28,800 Sure. 29 00:01:28,800 --> 00:01:31,800 A flashlight or the battery in your parents' car isn't made of lemons, 30 00:01:31,800 --> 00:01:33,800 but it works using the same principles. 31 00:01:33,800 --> 00:01:35,800 Can you use a lemon to power something? 32 00:01:35,800 --> 00:01:36,800 Let's see. 33 00:01:36,800 --> 00:01:38,800 I've got a little LCD clock. 34 00:01:38,800 --> 00:01:41,800 It normally works with a watch battery, about one and a half volts. 35 00:01:41,800 --> 00:01:44,800 Hook together some lemons like this, and let's see what happens. 36 00:01:46,800 --> 00:01:47,800 It's working! 37 00:01:47,800 --> 00:01:48,800 That's amazing! 38 00:01:49,800 --> 00:01:51,800 Can you think of another way to create electricity? 39 00:01:51,800 --> 00:01:52,800 How about solar power? 40 00:01:52,800 --> 00:01:54,800 Let's call it solar solution. 41 00:01:55,000 --> 00:01:56,000 That's quite a solar cell, isn't it? 42 00:01:56,000 --> 00:02:01,000 I saw on TV that NASA uses solar cells to power satellites and even the International Space Station. 43 00:02:01,000 --> 00:02:02,000 That's right. 44 00:02:02,000 --> 00:02:04,000 Look at this solar-powered bicyclist here. 45 00:02:05,000 --> 00:02:06,000 The brighter the light, 46 00:02:07,000 --> 00:02:09,000 the faster he pedals. 47 00:02:11,000 --> 00:02:16,000 So do you know how solar cells and batteries cause the charges to flow? 48 00:02:16,000 --> 00:02:17,000 What do you mean? 49 00:02:17,000 --> 00:02:19,000 Electricity doesn't appear out of nowhere. 50 00:02:19,000 --> 00:02:23,000 A very important law of physics says you can't get something for nothing. 51 00:02:23,200 --> 00:02:26,200 It takes work to push the charges through the wires, 52 00:02:26,200 --> 00:02:29,200 and the energy to do that work must come from someplace. 53 00:02:29,200 --> 00:02:32,200 With a solar cell, it uses the energy of the sun, 54 00:02:32,200 --> 00:02:34,200 and batteries use chemical energy. 55 00:02:34,200 --> 00:02:36,200 What other kinds of sources of electricity are there? 56 00:02:36,200 --> 00:02:38,200 A power company is the source of electricity. 57 00:02:38,200 --> 00:02:41,200 It's easy to plug into our outlets and get power. 58 00:02:41,200 --> 00:02:43,200 But I guess I don't know how they produce it. 59 00:02:43,200 --> 00:02:45,200 Do they use a battery? 60 00:02:45,200 --> 00:02:46,200 No, that's a good guess. 61 00:02:46,200 --> 00:02:50,200 A power company uses mechanical motion, however, to create electricity. 62 00:02:50,200 --> 00:02:51,200 Let me illustrate. 63 00:02:51,400 --> 00:02:54,400 Turn this crank, and tell me what happens. 64 00:03:01,400 --> 00:03:05,400 The faster I turn the handle, the brighter the light bulb glows. 65 00:03:05,400 --> 00:03:06,400 That's right. 66 00:03:06,400 --> 00:03:07,400 When you turn the handle, 67 00:03:07,400 --> 00:03:11,400 you're providing the energy to force the electrons to move through the wire. 68 00:03:11,400 --> 00:03:13,400 The motion that charges through the wire is called a current. 69 00:03:13,400 --> 00:03:16,400 Now this time, turn the crank, keep your eyes closed, 70 00:03:16,400 --> 00:03:18,400 and tell me when something happens. 71 00:03:21,400 --> 00:03:24,400 Wow, it's a lot easier to turn now. 72 00:03:24,400 --> 00:03:25,400 What happened? 73 00:03:25,400 --> 00:03:26,400 I screwed the light bulb. 74 00:03:26,400 --> 00:03:30,400 It only takes work to turn the crank as long as you're lighting the bulb. 75 00:03:30,400 --> 00:03:32,400 You're only lighting one bulb. 76 00:03:32,400 --> 00:03:35,400 Let's add some more bulbs, see if it's harder to turn the crank. 77 00:03:38,400 --> 00:03:39,400 Alright, go ahead. 78 00:03:39,400 --> 00:03:41,400 Whoa, it's a lot harder now. 79 00:03:41,400 --> 00:03:43,400 I'm really having to work at this. 80 00:03:45,400 --> 00:03:48,400 But Dr. D, obviously people don't turn the cranks on a power plant. 81 00:03:48,600 --> 00:03:50,600 What other sources of energy could you use 82 00:03:50,600 --> 00:03:52,600 other than people power to turn the crank? 83 00:03:52,600 --> 00:03:54,600 We can use wind power to turn the crank. 84 00:03:54,600 --> 00:03:56,600 Well, wind power is used to create electricity, 85 00:03:56,600 --> 00:03:59,600 but it's not often used for large-scale power production. 86 00:03:59,600 --> 00:04:02,600 I think the power plant in our town uses natural gas. 87 00:04:02,600 --> 00:04:03,600 That's right. 88 00:04:03,600 --> 00:04:06,600 Power plants use coal, oil, natural gas, 89 00:04:06,600 --> 00:04:09,600 and even nuclear fission to provide the energy to create electricity. 90 00:04:09,600 --> 00:04:11,600 In each of these cases, 91 00:04:11,600 --> 00:04:14,600 the burning of coal, oil, natural gas, 92 00:04:14,600 --> 00:04:17,600 and the fission of uranium provides the heat to produce steam. 93 00:04:17,800 --> 00:04:19,800 The steam causes a turbine to spin, 94 00:04:19,800 --> 00:04:23,800 which turns the crank and the generator producing the electricity. 95 00:04:23,800 --> 00:04:25,800 It's just like our experiment, but with more power. 96 00:04:25,800 --> 00:04:27,800 But there's another natural process 97 00:04:27,800 --> 00:04:29,800 that can be used to provide the energy to create electricity. 98 00:04:29,800 --> 00:04:31,800 You know what it is? 99 00:04:31,800 --> 00:04:33,800 Hmm, isn't it flowing water? 100 00:04:33,800 --> 00:04:34,800 That's right. 101 00:04:34,800 --> 00:04:37,800 When water flows downhill, it has the energy to turn the turbine. 102 00:04:37,800 --> 00:04:39,800 One of the most interesting power projects in the United States 103 00:04:39,800 --> 00:04:41,800 is at Niagara Falls. 104 00:04:41,800 --> 00:04:42,800 Why don't you check it out? 105 00:04:42,800 --> 00:04:43,800 Okay, I'll email them 106 00:04:43,800 --> 00:04:46,800 and see if we can talk to them about their facility.