1 00:00:00,000 --> 00:00:02,500 This plane is looking like a winner. 2 00:00:02,500 --> 00:00:06,000 Especially now that we put a rudder on our plane and we moved the wings back. 3 00:00:07,000 --> 00:00:08,500 It doesn't pitch. 4 00:00:08,500 --> 00:00:10,500 And it doesn't bank anymore. 5 00:00:10,500 --> 00:00:13,500 But I wonder if we're still missing something. 6 00:00:13,500 --> 00:00:16,500 Dr. D, we still have a few questions. You think you can help us? 7 00:00:16,500 --> 00:00:17,500 Sure. 8 00:00:17,500 --> 00:00:21,500 Thrust is needed, even when the plane is going at a constant speed. 9 00:00:21,500 --> 00:00:24,500 Why is that? Does it have anything to do with drag? 10 00:00:24,500 --> 00:00:29,500 Yes. Drag is what we call all the forces that act on an aircraft in a backward direction. 11 00:00:29,500 --> 00:00:32,000 Let's try an experiment. 12 00:00:32,000 --> 00:00:35,000 I'm going to push this cart. What happens? 13 00:00:36,500 --> 00:00:40,000 It looks like it's not slowing down. But you didn't keep pushing it. 14 00:00:40,000 --> 00:00:43,500 I didn't have to. Isaac Newton explained that once an object gets moving, 15 00:00:43,500 --> 00:00:48,000 it stays moving in a straight line at a constant speed unless you apply a force to it. 16 00:00:48,000 --> 00:00:50,000 Watch this other cart. 17 00:00:50,000 --> 00:00:54,000 It slows down right away. There must be some force acting on it. 18 00:00:54,000 --> 00:00:59,500 That's right. An object will only slow down if a force acts on it in the direction opposite to its motion. 19 00:00:59,500 --> 00:01:01,000 What might that force be? 20 00:01:01,000 --> 00:01:05,000 It looks like friction. That's the force when you rub two objects together. 21 00:01:05,000 --> 00:01:06,000 Very good. 22 00:01:06,000 --> 00:01:07,500 Was an airplane experience friction? 23 00:01:07,500 --> 00:01:10,500 An airplane experience is a type of drag called air resistance 24 00:01:10,500 --> 00:01:13,500 because of the air flowing over the wings and other parts of the body. 25 00:01:13,500 --> 00:01:16,000 Have you ever tried to drive your bicycle into the wind? 26 00:01:16,000 --> 00:01:18,500 Yes. It's really not very easy. 27 00:01:18,500 --> 00:01:21,000 You've had some experience with air resistance. 28 00:01:21,000 --> 00:01:25,000 So if the drag is less, we won't need as much thrust to keep it moving at a constant speed. 29 00:01:25,000 --> 00:01:26,000 Correct. 30 00:01:26,000 --> 00:01:30,000 So if we can find a way to reduce the air resistance, we've got it made. 31 00:01:30,000 --> 00:01:36,000 That's not exactly right. As it turns out, in addition to air resistance, there's another type of drag. 32 00:01:36,000 --> 00:01:38,000 This is getting complicated. 33 00:01:38,000 --> 00:01:40,000 Okay, we'll take air resistance first. 34 00:01:40,000 --> 00:01:43,500 To understand how to reduce air resistance, it would be best to talk to an expert. 35 00:01:43,500 --> 00:01:45,500 Of course, the best expert is nature. 36 00:01:45,500 --> 00:01:48,500 Nature? I wonder what that has to do with drag. 37 00:01:48,500 --> 00:01:52,500 Well, I know someone who observes nature to understand drag, and he can tell you all about it. 38 00:01:52,500 --> 00:01:55,500 His name is Ben Anders. He studies birds, fish, and even insects. 39 00:01:55,500 --> 00:01:57,500 That's our next stop. 40 00:02:00,500 --> 00:02:04,000 Look over there. That man looks like he's studying the fish. 41 00:02:04,000 --> 00:02:06,500 Dr. Anders, we're the treehouse detectives. 42 00:02:06,500 --> 00:02:07,500 Oh, hi. 43 00:02:07,500 --> 00:02:09,000 Dr. D said you could help us. 44 00:02:09,000 --> 00:02:11,000 We're trying to understand the force of drag. 45 00:02:11,000 --> 00:02:14,500 Dr. D says you use insects and marine life to help you in your research. 46 00:02:14,500 --> 00:02:18,500 Yes, I do. When I look at those shapes, I see airplane wings. 47 00:02:18,500 --> 00:02:20,500 Airplane wings? 48 00:02:20,500 --> 00:02:25,500 I guess I can see a slight comparison, but why would you want to compare them to airplane wings? 49 00:02:25,500 --> 00:02:33,500 At NASA, we study birds and insects and marine animals to inspire new research on flight and on ways to reduce drag. 50 00:02:33,500 --> 00:02:35,500 And we call this biomimetics. 51 00:02:35,500 --> 00:02:39,500 Wow, that's a big word. How do you do that kind of research? 52 00:02:39,500 --> 00:02:44,500 Well, let me ask you this. What do you think has a lower drag, a smooth surface or one with grooves in it? 53 00:02:44,500 --> 00:02:49,500 I'm not sure. I would guess a smooth surface would have less drag, but what's the right answer? 54 00:02:49,500 --> 00:02:52,500 Well, normally a smooth surface does have lower drag, 55 00:02:52,500 --> 00:02:58,500 but if you make the grooves very tiny and you shape them just right, the groove surface has lower drag. 56 00:02:58,500 --> 00:03:03,500 And we discovered that the shark's skin has those exact same tiny grooves to reduce his drag. 57 00:03:03,500 --> 00:03:06,500 I wonder what other secrets he's holding. 58 00:03:06,500 --> 00:03:11,500 This is so cool. I wonder if we need to make some adjustments to our plane to reduce its drag. 59 00:03:11,500 --> 00:03:13,500 Maybe we need to do a little more research. 60 00:03:13,500 --> 00:03:15,500 Let's go back to the treehouse. Bye. 61 00:03:15,500 --> 00:03:17,500 Bye.