1 00:00:00,000 --> 00:00:02,000 Hi, Dr. D. 2 00:00:02,000 --> 00:00:03,000 Hi. 3 00:00:03,000 --> 00:00:04,000 Hi, guys. 4 00:00:04,000 --> 00:00:06,000 Can you tell us what lightning is? 5 00:00:06,000 --> 00:00:08,000 Sure. Wait a minute, what brings this up? 6 00:00:08,000 --> 00:00:12,000 Well, I was telling Kaylee and Jacob that the power is still out across the street, 7 00:00:12,000 --> 00:00:14,000 but it's still on in our treehouse. 8 00:00:14,000 --> 00:00:16,000 We're trying to figure out why. 9 00:00:16,000 --> 00:00:17,000 Where are you going to start? 10 00:00:17,000 --> 00:00:18,000 We came up with a hypothesis. 11 00:00:18,000 --> 00:00:20,000 We think that lightning caused the power outage. 12 00:00:20,000 --> 00:00:22,000 It was a pretty big storm last night. 13 00:00:22,000 --> 00:00:24,000 How are you going to test your hypothesis? 14 00:00:24,000 --> 00:00:25,000 We're not sure. 15 00:00:25,000 --> 00:00:28,000 Well, to understand lightning, we first need to look at some basics. 16 00:00:30,000 --> 00:00:32,000 Let's rip up this paper. 17 00:00:32,000 --> 00:00:36,000 Now, comb your hair briskly and then bring the comb down close to the paper. 18 00:00:42,000 --> 00:00:43,000 Neat. 19 00:00:43,000 --> 00:00:45,000 Why did it do that? 20 00:00:45,000 --> 00:00:48,000 The ancient Greeks noticed the same thing when they rubbed amber with wool. 21 00:00:48,000 --> 00:00:50,000 Who's amber? 22 00:00:50,000 --> 00:00:53,000 Not who, but what. Amber is fossilized tree sap. 23 00:00:53,000 --> 00:00:55,000 Oh, okay. 24 00:00:55,000 --> 00:00:58,000 The amber picked up little objects like strands of fiber and hair, 25 00:00:58,000 --> 00:01:00,000 just like the comb picked up the paper. 26 00:01:00,000 --> 00:01:03,000 We say that the comb and the amber are electrically charged. 27 00:01:03,000 --> 00:01:06,000 Can other objects do the same thing? 28 00:01:06,000 --> 00:01:08,000 Sure. This balloon can pick up the paper, too. 29 00:01:16,000 --> 00:01:18,000 And it picks up other things, too, 30 00:01:19,000 --> 00:01:22,000 like this rice cereal and salt. 31 00:01:23,000 --> 00:01:25,000 The balloon will also stick to the wall. 32 00:01:29,000 --> 00:01:31,000 It can also attract the stream of water. 33 00:01:33,000 --> 00:01:35,000 Whoa! 34 00:01:36,000 --> 00:01:39,000 If you rub the acrylic rod with a plastic bag, it'll do the same thing. 35 00:01:40,000 --> 00:01:43,000 Now, how do you know that the balloon was charged and not the paper? 36 00:01:43,000 --> 00:01:46,000 Well, if an object is electrically charged, 37 00:01:46,000 --> 00:01:50,000 it should pick up objects like little pieces of paper or other such objects. 38 00:01:50,000 --> 00:01:52,000 Let's see. 39 00:01:54,000 --> 00:01:55,000 Nothing happened. 40 00:01:55,000 --> 00:01:56,000 Very good. 41 00:01:56,000 --> 00:01:59,000 A charged object will pick up other neutral and uncharged objects, 42 00:01:59,000 --> 00:02:01,000 but an uncharged object won't. 43 00:02:01,000 --> 00:02:03,000 Let's do an experiment with some tape. 44 00:02:03,000 --> 00:02:05,000 Bring this bar around. 45 00:02:10,000 --> 00:02:12,000 Put some tape on the table. 46 00:02:12,000 --> 00:02:14,000 I'll pull it up real quickly. 47 00:02:15,000 --> 00:02:17,000 And watch this. 48 00:02:21,000 --> 00:02:23,000 It attracted the paper. 49 00:02:23,000 --> 00:02:24,000 It must be charged. 50 00:02:24,000 --> 00:02:28,000 Now let's try two pieces of tape, one on top of each other. 51 00:02:34,000 --> 00:02:35,000 Hold on to that, please. 52 00:02:35,000 --> 00:02:37,000 How can we tell if these are charged? 53 00:02:37,000 --> 00:02:40,000 We need to do the paper scraps test to find out. 54 00:02:40,000 --> 00:02:41,000 Let's try it. 55 00:02:42,000 --> 00:02:44,000 Yep, they're charged all right. 56 00:02:45,000 --> 00:02:47,000 Well, here's the experiment. 57 00:02:48,000 --> 00:02:51,000 Let's hang up the single piece of charged tape. 58 00:02:52,000 --> 00:02:54,000 Now we'll pull up the double tape. 59 00:02:55,000 --> 00:02:57,000 Rehearse the top piece. 60 00:02:58,000 --> 00:03:00,000 It attracts the tape, just like before. 61 00:03:02,000 --> 00:03:04,000 It's repelling the second tape. 62 00:03:04,000 --> 00:03:05,000 We haven't seen that before. 63 00:03:05,000 --> 00:03:07,000 What conclusions can you make? 64 00:03:07,000 --> 00:03:11,000 Well, if an object is charged, it attracts uncharged items, 65 00:03:11,000 --> 00:03:14,000 but it may attract or repel other charged items. 66 00:03:14,000 --> 00:03:17,000 Does that mean there are two types of charges? 67 00:03:17,000 --> 00:03:18,000 That's right. 68 00:03:18,000 --> 00:03:20,000 Two types of charges are positive and negative. 69 00:03:20,000 --> 00:03:23,000 The top piece and the bottom piece have different charges. 70 00:03:23,000 --> 00:03:25,000 Now let's do this again. 71 00:03:25,000 --> 00:03:30,000 This time we'll take both pieces of tape in exactly the same way. 72 00:03:30,000 --> 00:03:31,000 So... 73 00:03:33,000 --> 00:03:35,000 They must have the same charge. 74 00:03:35,000 --> 00:03:36,000 That's right. 75 00:03:37,000 --> 00:03:39,000 Will they attract or repel? 76 00:03:42,000 --> 00:03:43,000 They repel. 77 00:03:44,000 --> 00:03:45,000 Let's see. 78 00:03:45,000 --> 00:03:48,000 If the charges are different, then they must attract. 79 00:03:48,000 --> 00:03:49,000 Let's find out. 80 00:03:49,000 --> 00:03:51,000 All right, we used the two tapes again. 81 00:03:52,000 --> 00:03:54,000 Both have different charges. 82 00:03:56,000 --> 00:03:58,000 How about that? 83 00:04:00,000 --> 00:04:01,000 Look at this machine. 84 00:04:01,000 --> 00:04:03,000 It's called a Van de Graaff generator. 85 00:04:03,000 --> 00:04:05,000 Jacob, stand up on this stool, if you would, 86 00:04:05,000 --> 00:04:07,000 and put your hands on top. 87 00:04:08,000 --> 00:04:12,000 I'm going to turn this machine on and transfer a lot of charge into you. 88 00:04:12,000 --> 00:04:14,000 It won't shock you, I promise. 89 00:04:15,000 --> 00:04:18,000 Wow, his hair is really standing out. 90 00:04:22,000 --> 00:04:25,000 Is it because all my hair is charged the same way 91 00:04:25,000 --> 00:04:29,000 and each strand is repelling or pushing away from the strand next to it? 92 00:04:29,000 --> 00:04:30,000 That's right. 93 00:04:30,000 --> 00:04:32,000 In the beginning, your body was neutral. 94 00:04:32,000 --> 00:04:34,000 It had the same number of positive and negative charges. 95 00:04:34,000 --> 00:04:36,000 All the positive charges, protons, 96 00:04:36,000 --> 00:04:38,000 and negative charges, electrons. 97 00:04:38,000 --> 00:04:41,000 When we transfer an awful lot of negatively charged electrons 98 00:04:41,000 --> 00:04:44,000 into your body, what kind of charge would you have then? 99 00:04:44,000 --> 00:04:49,000 Well, if the number of electrons and protons in his body were the same, 100 00:04:49,000 --> 00:04:51,000 then they would basically cancel each other out. 101 00:04:51,000 --> 00:04:53,000 And then if we added a lot of electrons, 102 00:04:53,000 --> 00:04:57,000 then I guess his body would be negatively charged. 103 00:04:57,000 --> 00:04:58,000 That's right. 104 00:04:58,000 --> 00:05:00,000 And I always thought you were the negative one. 105 00:05:00,000 --> 00:05:03,000 Now, if we turn the thing on again, 106 00:05:03,000 --> 00:05:05,000 build up a huge charge on top, 107 00:05:05,000 --> 00:05:08,000 move the second ball closer to the first, 108 00:05:08,000 --> 00:05:11,000 Wow, it looks just like lightning. 109 00:05:13,000 --> 00:05:15,000 Now, what's going on there? 110 00:05:15,000 --> 00:05:19,000 Well, the electrons are jumping from the Van de Graaff to the ball. 111 00:05:19,000 --> 00:05:22,000 It looks more like a flash of light than a bunch of particles. 112 00:05:22,000 --> 00:05:25,000 Well, I learned that you can't see electrons, 113 00:05:25,000 --> 00:05:27,000 so how can we see these electrons? 114 00:05:27,000 --> 00:05:28,000 Well, you're right. 115 00:05:28,000 --> 00:05:30,000 Electrons aren't too small to see. 116 00:05:30,000 --> 00:05:33,000 But as the electrons jump from the Van de Graaff to the ball, 117 00:05:33,000 --> 00:05:35,000 That's right. Electrons aren't too small to see. 118 00:05:35,000 --> 00:05:38,000 But as the electrons jump from the Van de Graaff to the ball, 119 00:05:38,000 --> 00:05:40,000 they heat up the air and cause it to glow. 120 00:05:40,000 --> 00:05:43,000 What you're seeing is the glowing air, not the moving electrons. 121 00:05:43,000 --> 00:05:44,000 Is this how lightning works? 122 00:05:44,000 --> 00:05:46,000 Yes, it's very similar. 123 00:05:46,000 --> 00:05:49,000 So, Dr. D., did we get electricity from lightning? 124 00:05:49,000 --> 00:05:51,000 Not quite. I'll tell you what. 125 00:05:51,000 --> 00:05:53,000 I'm going to line you up with a researcher 126 00:05:53,000 --> 00:05:55,000 at the NASA Langley Research Center in Hampton, Virginia. 127 00:05:55,000 --> 00:05:57,000 His name is Bruce Fisher. 128 00:05:57,000 --> 00:05:59,000 He's done a lot of studies on lightning. 129 00:05:59,000 --> 00:06:01,000 I'll arrange for you to meet him at the Virginia Air and Space Center. 130 00:06:01,000 --> 00:06:03,000 Great! Thanks, Dr. D. 131 00:06:03,000 --> 00:06:05,000 So, let's get up and go. 132 00:06:05,000 --> 00:06:06,000 Bye, Dr. D. 133 00:06:06,000 --> 00:06:07,000 Bye, guys.