Things You Thought You Knew – Need for Speed

Metric system, acceleration, and heat shields, Oh my! On this episode, Neil deGrasse Tyson and comic co-host Chuck Nice run us through some stuff you thought you knew: the metric system in the US, speed versus acceleration, and heat shields.

Speaker names marked ? are inferred from speaking time and the show’s known hosts — they are not voice-verified.

• 0:01Neil deGrasse Tyson?

  Welcome to StarTalk. Your place in the universe where science and pop culture collide. StarTalk begins right now. This is StarTalk. I am your host, Neil deGrasse Tyson, your personal astrophysicist, and I got my co-host, Chuck. Nice, Chuck, baby. Hey, what's happening, Neil? All right, all right. I bet you don't know what we're gonna do today. No. A new thing we're doing today. Uh-oh. This is gonna be a stuff you thought you knew, like a second installment of that. Right. We did this once before, and it really caught on, and people wanted a little more of that kind of action. It's because people want to know. They want to know.

• 0:45Neil deGrasse Tyson?

  They want to know more, more and more. They want to know new stuff, plus if the old stuff they knew was wrong, they want to fix it. Usually, most of the time. So, right off the top, just so you know, I'm gonna talk about the metric system in the United States. Interesting. Then I'm gonna talk about the difference between speed and acceleration. Okay. Then I'm gonna talk about heat shields of re-entering spacecraft. I'm looking to feel it. Okay, it's a little, it's an odd sort of collection there, but you'll feel it, I think, as we move through it, all right? So, let's start, let's start right out. Are you old enough to remember when Jimmy Carter said, "We're going metric in the United States"? This is the early 1970s.

• 1:30Neil deGrasse Tyson?

  Do you remember this? I do not. There was a whole commission to convert the United States to the metric system. Yes, well, good to know that that worked out so well. As I drink from my 16-ounce glass. So good to know. So good to know. So, I joke about this because back then and today, drug dealers have always been metric. Right. Just think about that. They don't sell cocaine in pounds, that's in kilos. That's right. So... That'd get you the same, that'd get you another measurement of time.

• 2:19Neil deGrasse Tyson?

  When Einstein hadn't explored yet.

• 2:21Chuck Nice?

  That's right. Yes, exactly.

• 2:25Neil deGrasse Tyson?

  So I've heard people joke that if we had put drug lords as head of the metric commission in the United States, we all would have been metric within months.

• 2:33Chuck Nice?

  Right. Wait, are you talking that afternoon?

• 2:36Neil deGrasse Tyson?

  That afternoon.

• 2:37Chuck Nice?

  That afternoon, we'd have been 100% metric and, and high.

• 2:44Neil deGrasse Tyson?

  So what I want to try to communicate is that we're not as bad as it may seem.

• 2:51Neil deGrasse Tyson?

  We are much farther along than we even admit to ourselves in this conversion. I just want to sort of put it out there. Okay. And I'm going to tell you why. Because I don't want you to feel bad about this. Now, I, as a scientist, we're metric from the beginning. That's not even a thing. Engineers are a little later in the, in the, in the listing, but scientists, we speak internationally, and that's the international system that gets used. Okay.

• 3:21Chuck Nice?

  Right.

• 3:21Neil deGrasse Tyson?

  So in fact, it's called système international, the SI system of units. The meter, the kilogram, the second is in there, but everybody uses the second. So, so you know, the French came up with the metric system. Did you know this?

• 3:35Chuck Nice?

  No wonder we don't use it.

• 3:43Neil deGrasse Tyson?

  Where do you get this editorial comment?

• 3:47Neil deGrasse Tyson?

  So it got implemented in 1789. And what was happening then in France?

• 3:54Chuck Nice?

  1789?

• 3:56Neil deGrasse Tyson?

  Yeah.

• 3:57Chuck Nice?

  89?

• 3:58Neil deGrasse Tyson?

  In part inspired by what happened in the United States.

• 4:01Chuck Nice?

  Was that the Bastille storming and all that good stuff?

• 4:04Neil deGrasse Tyson?

  The French Revolution, yeah.

• 4:05Chuck Nice?

  Right.

• 4:06Neil deGrasse Tyson?

  So part of that sort of overthrowing of all previous order, that was the occasion, if you're going to do it, that's a good time to do it. In addition to the rolling heads, you throw in the metric system.

• 4:16Chuck Nice?

  We need to figure out how these heads rule faster. How is it that we get the head to rule faster?

• 4:26Neil deGrasse Tyson?

  Okay.

• 4:27Chuck Nice?

  Do not put the basket down, let it roll, and we shall measure in a new way.

• 4:34Chuck Nice?

  I see the hair go from the guillotine all the way down. As I smoke a cigarette and watch.

• 4:43Neil deGrasse Tyson?

  Ah.

• 4:49Neil deGrasse Tyson?

  That's exactly how it happened.

• 4:50Chuck Nice?

  Yes.

• 4:53Neil deGrasse Tyson?

  All right, so they, uh, so do you know the original definition of a meter?

• 5:00Chuck Nice?

  No.

• 5:00Neil deGrasse Tyson?

  Okay, so somebody had to come up with that, right? I mean, it's pretty obvious a foot is somebody's foot, right? In the met, in the, in the imperial units, but a meter was one ten millionth the distance from the North Pole to the equator on a path that went through the Paris Observatory. So that's, that's how it began and that they became standardized. Then they created an artifact out of platinum and iridium, an alloy of those two. And that there was an etch mark on one end and on the other. And that was the length of the meter that you can go and reference it in France. So that you can then take a meter home with you. That was the correct line.

• 5:44Neil deGrasse Tyson?

  So that's an example, and they had an object called the kilogram. And it's in a vault and there it is, 1KG. Right, but point is it had a beginning and all of its metric beginning was in 1789. I'm just saying, okay.

• 5:58Chuck Nice?

  Okay.

• 5:59Neil deGrasse Tyson?

  Uh, so here we are in the United States and we, we kind of have metric envy, a combination of metric envy and, and imperial pride. All right, we're using Fahrenheit and inches and meters and cups and tablespoons and we're damn proud of it. But at the end of the day, I think it's like, yeah, maybe we kind of want a little bit of metric in our lives. So I just want to impress upon you, we already do. Are you ready?

• 6:25Chuck Nice?

  Okay.

• 6:25Neil deGrasse Tyson?

  Are you ready?

• 6:26Chuck Nice?

  I am ready.

• 6:27Neil deGrasse Tyson?

  And, and by the way, I'm saying we have been inching towards the metric system for decades.

• 6:33Chuck Nice?

  I see what you did there. Mm.

• 6:35Neil deGrasse Tyson?

  Mm-hmm.

• 6:36Chuck Nice?

  Uh-huh.

• 6:36Neil deGrasse Tyson?

  All right. Okay, so first of all, we had metric money.

• 6:44Neil deGrasse Tyson?

  From the start.

• 6:45Chuck Nice?

  Okay, this sounds like Bitcoin. I'm not sure if I'm in.

• 6:50Neil deGrasse Tyson?

  How many pennies in a dime? How many dimes in a dollar?

• 6:54Chuck Nice?

  Yeah, it's base 10, yeah.

• 6:55Neil deGrasse Tyson?

  It's it's base 10, all the way. At the time, England was using pounds and shillings and pence and that.

• 7:02Chuck Nice?

  And six pence.

• 7:03Neil deGrasse Tyson?

  I still don't know how that system worked. To this day, and I'm a full grown adult who've thought about it, okay? So, so first we had metric money. Put that in the bank, okay? All right. What else do we have? Oh, our photography has largely been metric from the beginning. All right, there's 35 millimeter film.

• 7:27Chuck Nice?

  Right.

• 7:27Neil deGrasse Tyson?

  You measure that in inches, right? You had a 50 millimeter lens.

• 7:31Chuck Nice?

  All lenses are measured in millimeter.

• 7:33Neil deGrasse Tyson?

  Measured in millimeter. Now, there was some film formats that were inches. There was four by five. And eight by 10, those are the larger formats, but most of all the others was metric. And the lenses were metric. You go to the movies, 70 millimeter wide, you know, 2001 A Space Odyssey, 1968, in 70 millimeters. No one was freaking out that you saw MM next to the 70.

• 7:56Chuck Nice?

  Right.

• 7:57Neil deGrasse Tyson?

  Okay, okay. So, photography was in. All right, what else was in? Oh, our medicine has been metric, like practically forever.

• 8:09Chuck Nice?

  Yeah.

• 8:09Neil deGrasse Tyson?

  All right, so you have, you know, it's one cc of some drug or one, it's, what is a cc? It's a cubic centimeter.

• 8:17Chuck Nice?

  Right.

• 8:17Neil deGrasse Tyson?

  That's what a cc is.

• 8:18Chuck Nice?

  No doctor gives you a shot of an ounce of penicillin. I need an ounce of penicillin stat, doctor. You're gonna kill him. He's dead, Jim.

• 8:30Neil deGrasse Tyson?

  He's already dead.

• 8:31Chuck Nice?

  He's already dead.

• 8:32Neil deGrasse Tyson?

  So, so medical dosing has been metric, like forever. Okay.

• 8:38Chuck Nice?

  Right.

• 8:38Neil deGrasse Tyson?

  Add to that, our nutrition labels.

• 8:43Neil deGrasse Tyson?

  Those were metric from the beginning. How many grams of fat?

• 8:48Chuck Nice?

  Oh.

• 8:49Neil deGrasse Tyson?

  How many milligrams of, okay?

• 8:51Chuck Nice?

  Right.

• 8:52Neil deGrasse Tyson?

  But just look on any nutritional label. It's all metric and it's been that way. And no one is freaking out by looking at this. Okay? How many grams this? How many grams that? So what do we have in the bank now? We got, we got metric money, metric medicine, metric photography, metric nutrition labels. What else? Oh, we've got metric bottles of soft drink. You've never in your life purchased a quart of Pepsi.

• 9:23Chuck Nice?

  Uh.

• 9:23Neil deGrasse Tyson?

  It's a liter.

• 9:24Chuck Nice?

  Yeah, it was a liter.

• 9:25Neil deGrasse Tyson?

  It's a liter.

• 9:26Chuck Nice?

  Right.

• 9:26Neil deGrasse Tyson?

  Okay. A liter is slightly more than a quart, but close enough, you know, for most purposes. But so one liter, two liter, three liter bottles of Pepsi.

• 9:36Chuck Nice?

  That's right.

• 9:36Neil deGrasse Tyson?

  Okay. So our larger volumes, non-dairy, larger bottles have been metric for a long time. Okay, for decades.

• 9:47Chuck Nice?

  It's funny because everything you're mentioning right now are all global commodities.

• 9:52Neil deGrasse Tyson?

  Yes.

• 9:52Chuck Nice?

  Soda is global.

• 9:54Neil deGrasse Tyson?

  Right.

• 9:54Chuck Nice?

  Photography is global.

• 9:56Neil deGrasse Tyson?

  Good point. We're not shipping milk. That's correct. That's correct.

• 9:58Chuck Nice?

  Yeah. Uh, pharmaceuticals are global.

• 10:02Neil deGrasse Tyson?

  Good point.

• 10:02Chuck Nice?

  It's all global stuff that you're talking about.

• 10:05Neil deGrasse Tyson?

  Well, let me keep going. All right.

• 10:06Chuck Nice?

  Okay.

• 10:06Neil deGrasse Tyson?

  I'm not done yet. One of the last things I thought would have changed.

• 10:11Chuck Nice?

  Okay.

• 10:11Neil deGrasse Tyson?

  Was the volume displacement of the pistons in an engine. Okay? I drove a car that was a 400 cubic inch V8 engine.

• 10:27Chuck Nice?

  That's right.

• 10:28Neil deGrasse Tyson?

  Nobody measures it in cubic inches anymore.

• 10:30Chuck Nice?

  Not anymore.

• 10:31Neil deGrasse Tyson?

  It's in liters.

• 10:32Chuck Nice?

  That's right.

• 10:33Neil deGrasse Tyson?

  Two liter. And that liter, if you ever wondered, is not the volume of any liquid in it. It's the volume of the cylinders in the engine block itself. So that's a measure of how much.

• 10:43Chuck Nice?

  4.0 liter. Yeah, that's right.

• 10:45Neil deGrasse Tyson?

  It's a measure of how much sort of movement and power you're getting out of the engine. It's one of several measures you can invoke. So that's metric. Okay, okay, and shall I keep going? Those are important things, I think. So there's like three holdouts: cooking, cooking measurements, distance, temperature, and baking. Okay? So when people say, "America, you gotta join us with the rest of the world with the metric system," we kind of already have A. B., I don't, I'm, I don't feel, even as a scientist speaking, I don't feel some great urge to give up Fahrenheit and feet and inches.

• 11:23Neil deGrasse Tyson?

  I'll tell you why. When you visit another country, um, part of what it is to sort of blend in and to fit in and to learn is to learn what their customs are. In America, Jack, we use Fahrenheit and just deal with it. Okay?

• 11:40Chuck Nice?

  That's right.

• 11:41Neil deGrasse Tyson?

  I mean, you know,

• 11:42Chuck Nice?

  I'm not going over to my neighbors and trying to borrow 236 milliliters of sugar.

• 11:49Chuck Nice?

  Hi, I'm new to the neighborhood. Do you have 236 milliliters of sugar?

• 11:54Neil deGrasse Tyson?

  Slam the door back in their face.

• 11:56Chuck Nice?

  Exactly.

• 12:00Neil deGrasse Tyson?

  So anyway, I think we come a long way. So we're inching, and maybe dairy comes next. I don't know. I kind of like the fact that, you know, eggs come in a dozen. A dozen is a nice historical baker's quantity.

• 12:12Chuck Nice?

  I like that.

• 12:13Neil deGrasse Tyson?

  And so I'm, I'm, I'm cool with that. One last point. Let me remind you that we had a mission to Mars where the engineers were using the Imperial system and the scientists were using the metric system. And there was a point where two calculations had to come together and their, their units were not converted to match. And so the propulsion that was put into play to go into orbit around Mars was the wrong thrust and it basically overshot Mars completely. And so we lost, you know, a hundred million dollar spacecraft. Because of not, because two systems didn't match. It's not because we weren't on metric. It's that people, yes, yes, it is that.

• 12:57Neil deGrasse Tyson?

  But it's because the because the system was not turned into a common set of measures. That that's why. Had that been done, we wouldn't have had the problem, even if the engineers continued to use feet and inches.

• 13:10Chuck Nice?

  Wow. That, that right, well, okay.

• 13:14Neil deGrasse Tyson?

  That was egg on our face. That was, that looked bad. Especially for NASA.

• 13:19Chuck Nice?

  Without a doubt.

• 13:20Neil deGrasse Tyson?

  Yeah.

• 13:20Chuck Nice?

  You know what I mean? It's like listed by that much.

• 13:25Neil deGrasse Tyson?

  Almost. It doesn't count. If you're trying to reach a planet, no, it doesn't count.

• 13:30Chuck Nice?

  Damn.

• 13:31Neil deGrasse Tyson?

  All right. So, so I just wanted to say we're inching towards the metric system and we're there in ways you probably hadn't thought about. And so that's my little bit of that.

• 13:41Chuck Nice?

  Yes.

• 13:41Neil deGrasse Tyson?

  And we're going to take a break. And when we come back, I want to talk about the difference between speed and acceleration.

• 13:48Chuck Nice?

  Right on.

• 13:48Neil deGrasse Tyson?

  When StarTalk returns.

• 14:01Speaker 02

  Hi, I'm Chris Cohen from Hallworth, New Jersey, and I support StarTalk on Patreon. Please enjoy this episode of StarTalk Radio with your and my favorite personal astrophysicist, Neil deGrasse Tyson.

• 14:21Neil deGrasse Tyson?

  We're back, StarTalk. This is a Stuff You Thought You Knew edition. I think it's our second installment, Chuck. We did this once before.

• 14:29Chuck Nice?

  Yes.

• 14:30Neil deGrasse Tyson?

  And I think you like it.

• 14:33Chuck Nice?

  I do. It's now called Stuff I Still Don't Know.

• 14:37Neil deGrasse Tyson?

  Still don't.

• 14:39Chuck Nice?

  Still don't know this stuff.

• 14:41Neil deGrasse Tyson?

  All right. So I want to talk about the difference between speed and acceleration.

• 14:45Chuck Nice?

  Okay.

• 14:46Neil deGrasse Tyson?

  All right. So there's a nice scene, nice. There's a rememberable scene in the movie Top Gun where they just came out of their, out of their planes and they're holding their helmet. And what, what does one of them say to the other as they high five each other?

• 15:04Chuck Nice?

  I've got the need for speed.

• 15:08Neil deGrasse Tyson?

  Okay. I thought it was I feel, I feel, I feel the need for speed.

• 15:12Chuck Nice?

  Oh, I feel the need, I got the need for speed, I feel the need for speed.

• 15:15Neil deGrasse Tyson?

  So there you go, I feel the need for speed and I wanna push back on that, if I may.

• 15:21Chuck Nice?

  Uh.

• 15:22Neil deGrasse Tyson?

  Okay.

• 15:22Chuck Nice?

  You wanna push back on the need for speed?

• 15:25Neil deGrasse Tyson?

  Yes, I am.

• 15:26Chuck Nice?

  Oh, no!

• 15:27Neil deGrasse Tyson?

  Cause I claim that their speed is almost irrelevant to what it is they're, they're, it's triggering their emotions.

• 15:37Chuck Nice?

  Really?

• 15:38Neil deGrasse Tyson?

  Yeah, yeah. Uh, because for example, right now, uh, at our latitude on Earth, the rotation of Earth is carrying us due east at 800 miles an hour.

• 15:52Neil deGrasse Tyson?

  The, are you saying, I feel the need for speed and this is great? No.

• 15:55Chuck Nice?

  Well, that may explain why I keep throwing up every time I, every time I stand up. It could be a reason why I vomit.

• 16:06Neil deGrasse Tyson?

  So no, but say, see, I'm about to say that what we think of as motion sickness is not motion sickness, it's acceleration sickness.

• 16:14Chuck Nice?

  Okay.

• 16:15Neil deGrasse Tyson?

  Okay, so Earth is in orbit around the sun 18 miles per second. That, all of these speeds are way faster than anything they're doing in their airplane.

• 16:25Chuck Nice?

  This is true.

• 16:26Neil deGrasse Tyson?

  So it's the not really after speed.

• 16:28Chuck Nice?

  Wow, 18 miles in a second.

• 16:30Neil deGrasse Tyson?

  In a second, one second.

• 16:32Chuck Nice?

  From my house, I would overshoot the Bronx. I mean, no, I would overshoot Brooklyn from where I am right now.

• 16:38Neil deGrasse Tyson?

  You'd end up in Long Island Sound.

• 16:40Chuck Nice?

  I would, I, oh, wow, in one second!

• 16:43Neil deGrasse Tyson?

  Okay, so you, you live in Jersey. You cross the Hudson River, the Withers, Manhattan, all of Brooklyn, and then you come out the other side.

• 16:52Chuck Nice?

  Oh, my God, that's amazing.

• 16:53Neil deGrasse Tyson?

  So here's the thing, when you are moving at constant speed, your body has no idea you're moving at any speed at all. Okay. It's only when your speed changes that you get some sense of motion.

• 17:13Neil deGrasse Tyson?

  And by definition, when your speed changes, it's an acceleration. Now, in physics, an acceleration can be positive or negative. In the English language, we have another word for when it's negative acceleration. It's just called what? Deceleration. Deceleration, okay. So I might say acceleration in my next few minutes. I mean, increasing or decreasing, it doesn't matter. So it's either positive or negative. Acceleration. Acceleration. When that happens,

• 17:44Neil deGrasse Tyson?

  you feel it, and that's what you're reacting to. All right? By the way, there's another way to change...

• 17:52Neil deGrasse Tyson?

  Think of velocity, okay? So velocity, change in velocity is an acceleration. And a velocity has a direction. But suppose you're banking a turn. Your direction is constantly changing. Well, if velocity has to have one direction, now I'm changing the direction, that's also an acceleration. So here's my point. When you're in a moving object, no matter its speed, if the direction or the speed changes, you are accelerating. And when you feel an acceleration, your body is going to respond. If you accelerate forward, your body will be thrown backwards. If you decelerate quickly, your body goes forward. If you bank a turn,

• 18:37Neil deGrasse Tyson?

  you lean against the door or against the person next to you in the front seat. So that's how you know you're accelerating, because your body is responding in this way. So these folks said, "I feel the need for speed." It's because they're doing barrel rolls in their plane and upside down and all the stuff they're doing. That's what they're feeling. But if they were going perfectly at Mach 1, 2, 3, 4, or 30, they wouldn't be saying, "I feel the need for speed." Because that's not anything they would notice. This has been the complaint about the Lexus car. When it first came out, the Lexus was a, you know, a luxury car, and that ride was smooth.

• 19:20Neil deGrasse Tyson?

  I read one commentary and it said, "It's like sitting on your living room couch while you're driving your car."

• 19:26Chuck Nice?

  Hmm, that sounds lovely.

• 19:29Neil deGrasse Tyson?

  So, nobody who feels the need for speed is buying a Lexus. They want a car that can bank turns and, and go from 0 to 60 in whatever how many seconds you're talking about. That's an acceleration.

• 19:41Chuck Nice?

  Yeah, but it doesn't sound good to say, "I feel the need for acceleration."

• 19:48Neil deGrasse Tyson?

  Okay, how about, I, I have to, hmm.

• 19:51Chuck Nice?

  It's a celebration of acceleration. Now I just sound like Jesse Jackson. Just, you know.

• 19:59Chuck Nice?

  That's what I'm saying.

• 20:00Neil deGrasse Tyson?

  My man rhymes anything that comes out of his mouth.

• 20:03Chuck Nice?

  Celebration of acceleration. Oh, keep hope, keep hope alive.

• 20:12Neil deGrasse Tyson?

  Okay, so, so that's all I'm trying to tell you. So that's why, they, they will give top speed when you're buying a car. They will give a top speed.

• 20:22Neil deGrasse Tyson?

  But they will also give 0 to 60, or 0 to 50, in a certain amount of time. So, that is the change in velocity over a certain amount of time. And the, so, if you change velocity in less, in less amount of time, your acceleration is higher and higher and higher. That's why they keep trying to drop the acceleration time. Then it's more head, it's more head snapping. Now.

• 20:44Chuck Nice?

  Right, yeah.

• 20:45Neil deGrasse Tyson?

  Now.

• 20:46Chuck Nice?

  That's why everybody loves Tesla.

• 20:49Neil deGrasse Tyson?

  Oh, because it, well, it's high, but it'd be true for, any well-made electric car will have very high acceleration. Even, even at low speeds, right. Teslas can accelerate 0 to 60 in 3, 4 seconds, right.

• 21:00Chuck Nice?

  Yeah.

• 21:00Neil deGrasse Tyson?

  Yeah, and I've been in it and you can feel it. It's like.

• 21:03Chuck Nice?

  Yeah.

• 21:03Neil deGrasse Tyson?

  Okay, okay, so now, watch. Let's kick it up a notch. You ready? I don't think you're ready. Are you seated?

• 21:08Chuck Nice?

  Okay, alright, I'm seated.

• 21:11Neil deGrasse Tyson?

  There is

• 21:11Chuck Nice?

  Strap in, hold on, cuz I don't wanna accelerate too fast, I better, I better strap in.

• 21:17Neil deGrasse Tyson?

  Okay, there is the, so if acceleration is the rate of change of your velocity, okay, so if that, if you rate changes quickly, you have high acceleration, you will feel this response all the more. Okay, alright. If acceleration is the rate and change in your velocity, what happens when you have a rate of change of your acceleration?

• 21:41Chuck Nice?

  Oh my goodness, let me guess, your head explodes.

• 21:46Neil deGrasse Tyson?

  Yes, well, okay, so if you have a rate of change of acceleration, that has a term in physics, it's called the jerk. Okay?

• 21:56Neil deGrasse Tyson?

  So

• 21:59Chuck Nice?

  Oh man, that's great.

• 22:00Neil deGrasse Tyson?

  Okay, so watch what happens, you ready?

• 22:02Chuck Nice?

  Go ahead.

• 22:02Neil deGrasse Tyson?

  Um, so I'm headed towards a brick wall. I'm trying to come up with these examples on the spot. Headed towards a brick wall, and I said, I should put on my brakes. So you put on your brakes.

• 22:11Chuck Nice?

  Right.

• 22:12Neil deGrasse Tyson?

  Okay, and while you put on your brakes, you feel yourself, you're leaning into the shoulder strap, okay?

• 22:18Chuck Nice?

  Okay.

• 22:19Neil deGrasse Tyson?

  When you hit the wall, your body jerks forward. Because you had a steady slowing down of your speed until your speed went to zero instantly. So that is a rate of change of your acceleration, and then you feel a jerk.

• 22:39Chuck Nice?

  Okay, but why, why did we run into a wall?

• 22:44Neil deGrasse Tyson?

  Okay, so the jerk is what actually does sort of musculoskeletal damage in an accident.

• 22:51Chuck Nice?

  Oh, okay.

• 22:52Neil deGrasse Tyson?

  Okay, because we can sustain an acceleration, but when they say I have 1G, 2G, those are pure constant accelerations. But if you go from 1G to 6Gs in an instant, your whole body snaps.

• 23:05Chuck Nice?

  Right.

• 23:06Neil deGrasse Tyson?

  That's, and so the jerk is

• 23:08Chuck Nice?

  And the same thing in reverse.

• 23:09Neil deGrasse Tyson?

  And the same thing in reverse, correct.

• 23:11Chuck Nice?

  That's, so what you're basically saying is, jumping out of a 20-story window doesn't kill you.

• 23:17Neil deGrasse Tyson?

  That's correct.

• 23:19Chuck Nice?

  It's, it's the ground that does, it's the ground.

• 23:27Neil deGrasse Tyson?

  If there were no ground, you'd be fine?

• 23:29Chuck Nice?

  You're fine.

• 23:32Chuck Nice?

  Oh, man.

• 23:35Neil deGrasse Tyson?

  So, so that's velocity, acceleration, and jerk. So, almost every, and, and there's some cars, they say, in this car, you can feel the road. If you ever test drive like a sports car, they tell you that, right? Well, what does it mean to feel the road? Well, if the, if the road were perfectly smooth, you wouldn't feel anything. So, the fact that the road has certain bumps, that the Lexus wouldn't feel those bumps because the tires are adjusting to it. But your sports car, which has, quote, rigid suspension, it is rigid enough so that you're feeling that, right? So, you and the road and the bumps and wiggles and the turns and twists on the road, you're feeling it all.

• 24:14Chuck Nice?

  Nice.

• 24:15Neil deGrasse Tyson?

  You feeling it. And so you, so this is what you like, this is what you seek. This is what the sports enthusiast is actually after, even if they're not self-conscious of it. Because if they only want at high speeds, you can just get on a, you know, get on a high-speed train. And then you don't feel it because they're smooth. No, you want to, you want to bank the turns and feel it.

• 24:37Chuck Nice?

  That reminds me of a, a guy on the, I was on the turnpike and a guy comes by on a motorcycle and he's already, I'm doing 80, so he had to be doing a little faster than 80 because he came by me. And then he pulls back on the throttle and pops a wheelie at 80 miles an hour. And pulls off.

• 24:56Neil deGrasse Tyson?

  Okay.

• 24:58Chuck Nice?

  So...

• 25:01Chuck Nice?

  And, and I, and I'm pretty sure he was like, "I feel the need for acceleration."

• 25:08Neil deGrasse Tyson?

  And with the high-accelerating cars, of course, a constant acceleration is a, is a one-time thing. By the way, you either press yourself back or forward or lean one way or another, and any abrupt change in that creates this, this jolt. But, but even if you, if you're, if you're going at zero and then you floor it, there is the initial head snap, okay? That's a very high moment of acceleration, but then you stays that way until you, like, hit the brick wall and then you're snapping another way. So, anyway, I just put, I'm just putting all this out there, in case you didn't know.

• 25:42Chuck Nice?

  So, uh, all I can say is, please take Neil's word for everything he just said. Let's not try the brick wall experiment for ourselves. Okay? We're not responsible for anybody who crashes their car into a wall. All right? Just take his word for it.

• 26:01Neil deGrasse Tyson?

  Chuck, one last thing.

• 26:02Chuck Nice?

  Okay.

• 26:03Neil deGrasse Tyson?

  All right? So if you're in an airplane and the airplane wants to just go left, let's say.

• 26:09Chuck Nice?

  Right.

• 26:09Neil deGrasse Tyson?

  In the old days-

• 26:10Chuck Nice?

  First it puts on its blinker.

• 26:12Neil deGrasse Tyson?

  Put the, roll down a window, put the hand out.

• 26:14Chuck Nice?

  Roll down the window, put his hand, pilot puts his hand out.

• 26:17Neil deGrasse Tyson?

  All right. So, so in the old days, the plane would turn and you would feel yourself leaning one direction or another. Depending on which direction it was turning. And if you had sort of a drink in your glass, you would see the level of the liquid tip inside the glass.

• 26:35Chuck Nice?

  Right.

• 26:36Neil deGrasse Tyson?

  That doesn't happen anymore.

• 26:38Chuck Nice?

  What?

• 26:39Neil deGrasse Tyson?

  Yep. It doesn't happen anymore.

• 26:41Chuck Nice?

  Okay.

• 26:41Neil deGrasse Tyson?

  Because-

• 26:41Chuck Nice?

  Now, why wouldn't that happen?

• 26:42Neil deGrasse Tyson?

  Computers fly airplanes. The pilot's there just for show. All right? Computers fly airplanes. And here's what it does. When you're just sitting there doing nothing on an airplane going nowhere, gravity points straight down into your chair. You have a glass of water? Gravity points vertically down, so the water level is horizontal. Okay? Now the plane takes off. While it's gaining speed, you press back. You'll see the liquid, you're not being served liquid at this point, but it would actually change what it thinks is horizontal while you're accelerating. All right?

• 27:15Chuck Nice?

  Right.

• 27:15Neil deGrasse Tyson?

  So now you get up to, you know, 30,000 feet. You're going 500 miles an hour. That's speed, way faster than any car anybody's driving today. So, um, so there it is. And everything is level and horizontal once again. So now watch what happens. If, while the plane makes a left turn, depending on its speed, it can angle the fuselage.

• 27:43Neil deGrasse Tyson?

  So that your urge to lean to the right in that case is compensated by the banking of the plane itself. And so, and the computer does it perfectly. So if you have a drink and you're sitting there, the plane can make a complete circle. And you will never notice it. Because the combination of all the vectors line up in that computed trajectory of the plane so that everything goes straight into the bottom of the plane and into the chair. Even though everybody's actually tipped to the side, the fact that it's on a banked turn compensates for that. And so your drink is always horizontal.

• 28:28Neil deGrasse Tyson?

  That's why if your blinds are closed, you'll never even know you're returning. Next time you come into the airport, do this experiment. Get your drink, put it there, notice its level, open the slide, open the shade, look out the window and watch the plane turn to come in for a landing. And as it does it, the water level is completely horizontal in your glass.

• 28:50Chuck Nice?

  That's cool. The only problem, though, is the computer can't talk to you and that disaffected, "I'm bored out of my mind" comforting pilot voice like, "Ladies and gentlemen, we're on our final descent to JFK. Just want to let you know that we know you have other choices to fly and we thank you for flying with us. If you look out the left side of your plane, don't do that. You should look at the water in your glass right now."

• 29:12Neil deGrasse Tyson?

  Exactly. Do some science while you're doing it. All right. So when we come back, I've got another segment here of stuff you thought you knew. So Chuck, you want another one of these?

• 29:24Chuck Nice?

  I want another one. Any hints on what it might be?

• 29:27Neil deGrasse Tyson?

  Oh, yeah. It's just on heat shields.

• 29:31Chuck Nice?

  Oh, sweet.

• 29:32Neil deGrasse Tyson?

  Let's do it.

• 29:33Chuck Nice?

  All right.

• 29:33Neil deGrasse Tyson?

  Okay, all right. StarTalk returns.

• 29:44Chuck Nice?

  Hey, let's give a Patreon shout out to the following Patreon patrons. Ray Souza, John Delano, and Louis Serrignano. Guys, we couldn't do this show without you. Thank you so much for your support. And for those of you who are listening and would like your very own Patreon shout out, please go to patreon.com/startalkradio and support us.

• 30:12Neil deGrasse Tyson?

  We're back, StarTalk. Chuck Nice tweeting at Chuck Nice Comic. Dude.

• 30:15Chuck Nice?

  Thank you, sir. Yes.

• 30:16Neil deGrasse Tyson?

  You've got some good stuff lately. Keep it going.

• 30:18Chuck Nice?

  Thank you.

• 30:19Neil deGrasse Tyson?

  All right. All right. So we're still doing stuff you thought you knew, or stuff...

• 30:23Chuck Nice?

  Stuff you still don't know?

• 30:24Neil deGrasse Tyson?

  Or still don't care about? I don't know. So I want to talk about heat shields.

• 30:29Chuck Nice?

  All right.

• 30:30Neil deGrasse Tyson?

  Okay?

• 30:31Chuck Nice?

  Yeah.

• 30:31Neil deGrasse Tyson?

  So we all know that they exist. And do you know why they exist?

• 30:35Chuck Nice?

  To stop phasers from penetrating the ship's hull?

• 30:38Neil deGrasse Tyson?

  I didn't say...

• 30:43Neil deGrasse Tyson?

  I... That's a different kind of shield. I'm not talking about heat shields.

• 30:47Chuck Nice?

  Damn.

• 30:48Neil deGrasse Tyson?

  Not phaser shields.

• 30:49Chuck Nice?

  Aw, man!

• 30:51Neil deGrasse Tyson?

  Damn. Oh, you don't want to hang around anymore, okay? Ordinary heat shields, okay?

• 30:57Chuck Nice?

  Okay.

• 30:58Neil deGrasse Tyson?

  You've always seen, you've heard about it, you've read about it. And do you know what they're for?

• 31:03Chuck Nice?

  Um, I would guess because it gets hot. So they're going to shield you from the heat.

• 31:10Neil deGrasse Tyson?

  Okay, that's not their purpose.

• 31:12Chuck Nice?

  What?

• 31:13Neil deGrasse Tyson?

  Yeah, that's not, that's not why they exist.

• 31:15Chuck Nice?

  Well, that's a very deceptive name, Ben.

• 31:17Neil deGrasse Tyson?

  Yes, it is.

• 31:20Neil deGrasse Tyson?

  I thought about that. That's right.

• 31:21Chuck Nice?

  Yeah. That's an extremely deceptive name.

• 31:26Neil deGrasse Tyson?

  It implies that you're gonna get hot and burn up, so you have to protect yourself from it, and so you put on these shields so that you don't die.

• 31:34Chuck Nice?

  So why is NASA toying with my emotions like this?

• 31:37Neil deGrasse Tyson?

  This, because now you can, because astronauts is living, fleshy things inside the capsule.

• 31:42Chuck Nice?

  Right.

• 31:43Neil deGrasse Tyson?

  Okay.

• 31:43Chuck Nice?

  So if it's not to stop me from burning up and dying, what's it for?

• 31:48Neil deGrasse Tyson?

  Okay. So here it is. Ready?

• 31:50Chuck Nice?

  Go ahead.

• 31:51Neil deGrasse Tyson?

  You need heat shields because...

• 31:55Neil deGrasse Tyson?

  Any object in orbit is going, especially low Earth orbit, is going 18,000 miles an hour.

• 32:03Chuck Nice?

  Right.

• 32:04Neil deGrasse Tyson?

  Okay?

• 32:04Chuck Nice?

  That's right.

• 32:05Neil deGrasse Tyson?

  That's fast. So if you do the math, that's like five miles per second.

• 32:08Chuck Nice?

  Second.

• 32:09Neil deGrasse Tyson?

  Eight kilometers a second, alright? So, that's fast. Well, if you're going that fast in any other situation, you'd put on the brakes, right? You would find some way to slow down.

• 32:21Chuck Nice?

  Right.

• 32:21Neil deGrasse Tyson?

  Well, spacecraft don't also carry fuel to slow down with.

• 32:29Chuck Nice?

  No retro-rockets?

• 32:30Neil deGrasse Tyson?

  No retro-rockets.

• 32:30Chuck Nice?

  Well, now they do.

• 32:32Neil deGrasse Tyson?

  Well, no, not really. No. Well, well, it depends. Wait, hold on. When they're coming back to Earth, no retro-rockets.

• 32:37Chuck Nice?

  Okay, still no retro-rockets.

• 32:38Neil deGrasse Tyson?

  Still no retro-rockets. So, but you're right. It would be called retro-rockets. So, yeah, I'm going so fast, let me flip the engine the other way, or point the nozzle, and blow exhaust opposite the direction I'm going, that will slow me down.

• 32:52Chuck Nice?

  Right.

• 32:52Neil deGrasse Tyson?

  Okay, if we had that, that's all you'd have to do to come out of orbit, is blow exhaust out the other direction until you have zero velocity, pop a parachute, and then glide down to Earth.

• 33:07Chuck Nice?

  Yeah, like, like in a ship, like, all engines reverse, you know? And you see the propeller stop and go the opposite direction.

• 33:14Neil deGrasse Tyson?

  Correct, correct. Okay, that's all you'd have to do. But, to carry the fuel that you're not gonna use until you wanna come out of orbit, that takes fuel to put the fuel that you're not burning. And so, we said, "We're not gonna do this, because we don't have to." Let's take all of this kinetic energy, this energy of motion, and let the atmosphere burn it off. Let the atmosphere sweep it away.

• 33:47Neil deGrasse Tyson?

  So they're called heat shields, but you know what they are? They're aero braking. It's an aero braking system. Uh huh. You want this because you intentionally didn't bring fuel or brakes to slow you down. So you use air to do it. So what do they do? Here's the capsule in orbit, move in real fast. Okay. And it's set up in such a way that the bottom section, uh, it'll always sort of dangle with that coming first. And it's, it's this big blunt thing that plows into the atmosphere. The atmosphere is, I'm not going to want to let you do that, but I'm coming through anyway. It's not aerodynamic at all. It's totally not. Well, it's aerodynamic in that it's not going to be turbulent.

• 34:32Neil deGrasse Tyson?

  Um, it'll stably come through. But, right, you are, you want to maximize this resistance. And in so doing, you heat up the bottom side of the craft. Where does the energy come from that's heating the bottom of the craft? The air friction. I know, but, and, okay. What was the original source of that energy? What do you mean? It was your speed of the craft. Oh, that's right. The craft itself flying in at 18,000 miles an hour. Thank you. We gotta get rid of that energy somehow. So, so here it comes. All right, let us come down and work our way into the atmosphere. And in the upper layers, there's not as much air molecules, but there it is.

• 35:15Neil deGrasse Tyson?

  And you get sort of shock waves and friction and all manner of other sort of communicating molecules. All right. And that speed becomes heat energy. The kinetic energy becomes heat energy. Now, if it only becomes heat energy, that's not good enough because then you'll still burn up. You've got to whisk away that heat energy somehow. Hmm, right. Okay. Send it somewhere else. Get it out of here. So in the old days, and even in many modern capsules, the quote "heat shields" are onion layers of burnable substance.

• 35:49Chuck Nice?

  Oh, so they are heating up and then they're peeling away.

• 35:53Neil deGrasse Tyson?

  Peeling away.

• 35:54Chuck Nice?

  So the, so all the heat is actually like wicking, like moisture wicking.

• 36:00Neil deGrasse Tyson?

  I like that. I like that analogy. You're wicking away the heat. And every time you do this, the thing is slowing down and continues to slow down. And depending on how much kinetic energy you have, add on a few more layers. Okay? When they came back from the moon, they re-entered the atmosphere at a higher speed than just coming out of low Earth orbit. So the mooncrafts coming back had more heat shield layers than the other spacecraft.

• 36:27Chuck Nice?

  Wow. That, by the way.

• 36:29Neil deGrasse Tyson?

  It's aerobraking. That's what it is.

• 36:30Chuck Nice?

  That is ingenious.

• 36:31Neil deGrasse Tyson?

  It is, and it's blunt, and it's low-tech, and it worked every time.

• 36:35Chuck Nice?

  I don't know who thought of that, but that guy should have got a doughnut. I'm telling you, that, or a parking space. He should have got something. He should have got a parking space, cuz that is...

• 36:47Neil deGrasse Tyson?

  Says The New Yorker, where parking space is highly valuable.

• 36:50Chuck Nice?

  Somebody, somebody was really thinking. I mean...

• 36:53Neil deGrasse Tyson?

  Yeah, and it works, and it, and it works every time. And so, so, so, and so it's, I think the, the correct word is "it ablates." Ablates. You were, you were saying whisking, it ablates. And so, and it, it goes away. And when you're done and you have low enough speed, then you deploy your parachute and you just dip, dip in.

• 37:10Chuck Nice?

  That is genius.

• 37:12Neil deGrasse Tyson?

  There is a sci-fi movie where they are in orbit around some planet. I think it might be Mars, but it's some planet. I don't remember which. And they're on some stable orbiting platform. But there's one of these platforms that sort of rotates with the rotating planet. Okay, and a guy falls off the platform towards the planet. And that's bad, and you see, and then he goes down, and then you see him disappear in a puff of smoke.

• 37:39Chuck Nice?

  No! No! No!

• 37:43Neil deGrasse Tyson?

  Just because you're entering an atmosphere doesn't mean you're gonna burn up. The burning up is not an inherent feature of passing through an atmosphere. The burning up comes from getting rid of the speed you had to maintain 18,000 miles an hour. That's all I'm saying. Now, when we landed on the moon, moon's got no atmosphere.

• 38:02Chuck Nice?

  Right.

• 38:02Neil deGrasse Tyson?

  How do you get a soft landing there? Can't use a parachute. Can't use aero braking. They needed retro rockets. Gotta have retro rockets. Yeah. Yep. There it is. Mars has a thin atmosphere. So that one had parachute, big parachute, plus retro rockets, plus aero braking. All three to get the rovers on Mars. Or you drop a trampoline.

• 38:27Neil deGrasse Tyson?

  Thank you. Well, I'll bring that up at the next NASA meeting, okay? Chuck Nice says, "Trampoline."

• 38:36Neil deGrasse Tyson?

  So why did it take us five days to land on the moon?

• 38:42Neil deGrasse Tyson?

  Yeah, if it's a perfect trampoline, it will never stop. It'll never dissipate the energy. It'll just keep bouncing, right? You want it to. The energy has to dissipate somehow. It'd heat up the springs. The energy can't just disappear. It has to transmute it to some other form and then get whisked away, as you said. So you should, I think you should always think of heat shields as aero braking systems rather than, "Oh, you need this, otherwise you'll burn up." No, you need it, otherwise you'll crash. That's so cool. That's really cool. And there you go. Oh, and in the movie 2010, ostensibly the sequel to 2001, they came to Jupiter and they aero braked around Jupiter. They had some really good visual effects for the day. And inside the craft is saying,

• 39:25Neil deGrasse Tyson?

  "Oh, wow, this is, I wish I could see this." From the outside, this aero braking. Basically, any spacecraft with heat shields coming through an atmosphere is aero braking. Right. Anytime. So that was not some new thing. It was portrayed as some new innovative concept. But of course, we do that all the time. In fact, there are spacecraft that come into Mars and their orbit is highly elongated. That's a higher energy orbit. And they want to sort of circularize it. So when it dips down closer to the atmosphere, it makes sure that the atmosphere slows it down a little bit. That eats some of the energy. And you can circularize an orbit on purpose that way. So they just kind of like skipping rocks? Skipping rocks? I like that.

• 40:10Neil deGrasse Tyson?

  I like that. That's cool. So there you go Chuck. Think of it as air breaking, not heat shields for the future.

• 40:18Chuck Nice?

  Very nice. Do not try this on Earth. That's all I can say. Please don't try this on Earth. But that is a really cool concept.

• 40:25Neil deGrasse Tyson?

  And if you fall out of your spaceship and fall towards a planet.

• 40:29Chuck Nice?

  Right.

• 40:30Neil deGrasse Tyson?

  If you die, it won't have to be because you burned up.

• 40:33Chuck Nice?

  Right. It'd just be because you hit the planet.

• 40:38Chuck Nice?

  Either way, that dude was gonna die. So.

• 40:43Neil deGrasse Tyson?

  All right. This was yet another episode of Stuff We Thought You Should Know, whether or not you did.

• 40:52Neil deGrasse Tyson?

  All right Chuck, Chuck, my co-host.

• 40:54Chuck Nice?

  Always a pleasure.

• 40:55Neil deGrasse Tyson?

  All right. Neil deGrasse Tyson, as always, keep looking up.