Things You Thought You Knew - Metric system, acceleration, and heat shields with Neil deGrasse Tyson

[Music] this is star talk i'm your host neil degrasse tyson you're a personal astrophysicist and i got my coho chuck nice checking baby hey what's happening neil all right all right i bet you don't know what we're gonna do today no 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 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 going to talk about the metric system in the united states then i'm going to talk about the difference between speed and acceleration then i'm going to talk about heat shields of re-entering spacecraft interesting okay that's a little it's an odd sort of collection there but there's you'll feel it i think as we move through it all right so let's 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 this is the early 1970s 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 [Laughter] as i drink from my 16-ounce glass [Laughter] so good to know so good to know um so so i joke about this because back then and today um 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'll get you the same that that gets you another measurement of time one that einstein had hadn't explored yet that's right yes exactly 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 right wait are you talk that afternoon after that afternoon we'd have been 100 metric and and high so what i want to try to communicate is that we're not as bad as it may seem 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 is a scientist we're metric from the beginning right that's not even a thing engineers are a little later in the in the in the listening but scientists we speak internationally we and that's the international system that gets used okay right so in fact it's called system 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 no wonder we don't use it [Laughter] when you get this editorial card so it got implemented in 1789 and what was happening then in france 1789. 89. in part inspired by what happened in the united states uh was that the best deal storming and all that yeah french revolution yeah right yeah so part of that sort of overthrowing of all previous order that was the occasion if you're gonna do it that's a good time to do it right in addition to the rolling heads you throw in the metric system we need everywhere to figure out how these heads roll faster how is it that we get to head to rava we're gonna put the basket down let it roll and we shall measure it in no way i seize your hair go from the guillotine as it went down as i smoke a cigarette and watch [Laughter] that's exactly how it happened all right so they uh so do you know the original definition of a meter no okay so somebody had to come up with that right 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 1 10 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 uh in france uh so that you can then take a meter home with you that was the correct line so that's an example and they had an object called the kilogram and it's in at vault and there it is 1 kg all right but point is it had a beginning and all this metric beginning was in 1789 i'm just saying okay okay so 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 i am ready and and by the way i'm saying we've been inching towards the metric system for decades i see what you did there okay so first of all we had metric money from the start okay this sounds like bitcoin i'm not sure if i'm in how many pennies in a dime how many dimes in a dollar yeah all right base 10 yeah it's it's base 10 all the way at the time england was using pounds and shillings and pence and that and i said 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 right you didn't measure that in inches right you had a 50 millimeter lens all lenses are measured all lenses are measured in now there was some film formats there were inches there was four by five right and eight by ten those are the larger formats but most of all the others was metric and the lenses were metric you go to the movie 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. right okay okay so photography was in all right what else was in oh our medicine has been metric like practically forever 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 that's what a cc is no doctor gives you a shot of an ounce penicillin [Laughter] i need an ounce of penicillin stat doctor you're gonna kill him he's dead jim he's already dead he's already dead so so medical dosing has been metric like forever okay uh add to that our nutrition labels were metric from the beginning how many grams of fat oh that's how many milligrams okay 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 banknote we got we got metric money metric medicine metric photography metric um nutrition labels what else oh we've got metric bottles of soft drink you've never in your life purchased a quart of pepsi i have a leader no you haven't it's a liter okay a liter slightly more than a quart but close enough you know for most purposes but so one liter two liter three liter bottles of pepsi that's right okay so uh our larger volumes non-dairy larger bottles have been metric for a long time okay for decades it's funny because everything you're mentioning right now are all global commodities yes soda is global photography is global good point we're not shipping milk that's correct right yeah uh pharmaceuticals are global it's all global stuff that you're talking okay well well let me keep going all right okay i'm not i'm not done yet one of the last things i thought would have changed okay was the volume displacement of the pistons in an engine okay i drove a car that was a 400 cubic inch v8 engine that's right nobody measures it in cubic inches anymore not anymore it's in liters that's how you one liter two lead and that leader if you ever wondered is not the volume of any liquid in it is the volume of the cylinders in the in the engine block itself 4.0 liter yeah that's right it's a measure of how much sort of uh 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 uh shall i keep going about it those are important things i think okay now we still have fahrenheit yes and we still have sort of miles and and our cooking is not really metric so it's like three holdouts cooking distance cooking measurements distance temperature and baking okay right so when people say america you got to 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 in inches 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 i mean you know i'm not going over to my neighbors and trying to borrow 236 milliliters of sugar i'm new to the neighborhood do you have 236 milliliters of sugar so anyway i think we come a long way so we're inching and maybe dairy comes next i don't know um i kind of like the fact that you know eggs come in a dozen a dozen is a nice historical baker's quantity i like that and so i'm i'm cool with that 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's 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 100 million dollar spacecraft because of not because two systems didn't match it's not because we weren't on metric it's that because the system was not turned into a common um 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 a feet and then inches wow that that right well okay that was egg on our face that was that looked bad especially for nasa without a doubt yeah what do you mean yeah it's like missed it by that much almost it doesn't count yeah if you're trying to reach a planet no it doesn't count damn oh yeah that's awful yeah all right 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 yes and we're going to take a break and when we come back i'm going to talk about the difference between speed and acceleration right on when star talk returns we're back star talk this is a stuff you thought you knew edition i think it's our second installment chuck we did this once before yes and i i it's i i think you like it i do it's now called stuff i still don't i know don't know this stuff all right so for this middle segment i want to talk about the difference between speed and acceleration okay okay all right so there there's a nice scene nice there's a rememberable scene in the movie top gun where they just came out of there 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 i've got the need for speed okay i thought it was great i feel i feel the need for speed and i want to push back on that if i may okay you want to push back on the need for speed yes i am oh no because i claim that their speed is almost irrelevant to what it is their ex their it's triggering their emotions really yeah yeah 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 are you saying i feel the need for speed and this is great no you may explain why i keep throwing up every time every time i stand up it could be a reason why i vomit 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 okay 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 this is true so if they're not really after speed wow 18 miles in a second in a second one second from my house i would overshoot the bronx i mean you know i would overshoot brooklyn yeah where i am right now you'd end up in the long island sound right in one second okay so you you live in jersey you cross the hudson river the width of manhattan all over brooklyn and then you come out water oh my god that's amazing 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 and by definition when your speed changes it's an acceleration now in physics an acceleration can be positive or negative in in the english language we have another word for when it's negative acceleration and it's just called what deceleration deceleration okay so so i might say acceleration in this in my next few minutes i mean increasing or decreasing it doesn't matter either positive or negative excel accelerate okay when that happens you feel it and that's what you're reacting to all right by the way think of velocity okay so velocity a change in velocity is an acceleration but sup and a velocity has a direction right 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 s if you decelerate quickly your body goes forwards if you bank a turn you lean against the door or breaks the person next to you in the front seat so that's how you know you're accelerating because your body is responsible 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 was 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 i read one commentary and it said it's like sitting on your living room couch while you're driving your car that sounds lovely okay so nobody who feels the need for speed is buying a lexus they want a car that can bank turns and and go from zero to 60 in whatever how many seconds you're talking about that's an acceleration yeah but it doesn't sound good to say i feel the need for acceleration [Laughter] it's a celebration of acceleration now i just sound like jesse jackson you know that's what i'm saying it's because my man rhymes anything it comes out of his mouth celebration of acceleration keep alive okay so so that's all i'm trying to tell you so that's why they'll they will give top speed when you're buying a car they will give a top speed um 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 so if you change velocity in less and 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 ahead it's more head snapping now right yeah now actually let's take a look at tesla oh because it was high right but it'd be true for any well-made electric car will have very high acceleration yeah even at low speeds right teslas can accelerate 0-60 in three four seconds yeah that's good yeah and i've been in it and you can feel it it's like yeah okay okay so now watch let's kick it up a notch you ready i don't think you're ready are you seated okay all right i'm sorry okay there it is hold on i don't want to accelerate too fast i better strap it okay 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 all right if acceleration is the rate and change in your velocity what happens when you have a rate of change of your acceleration oh my goodness let me guess your head explodes 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 all right so so watch this oh man that's great okay so watch what happens you ready go ahead um so i'm headed towards a brick wall i'm trying to come up with these examples on the spot heading towards a brick wall and so i should put on my brakes so you put on your brakes okay and while you put on your brakes you feel yourself you're leaning into the the shoulder strap okay 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 okay but what why don't we run into a wall okay so the jerk is what actually does sort of musculoskeletal damage in an accident okay okay because we can sustain an acceleration when they say i have one g two g those are pure constant accelerations but if you go from one g to six g's in an instant your whole body snaps right that's this and so the jerk is one reverse and the same thing reversed correct so what you're basically saying is jumping out of a 20-story window doesn't kill you that's correct if there were no ground right he's alright oh man so so that's uh velocity uh acceleration and jerk so almost every 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 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 all right so you and the road and the bumps and wiggles and the turns and twists on the road you're feeling it all nice you feeling it and so you get 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 that reminds me of 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 okay so and and i and i'm pretty sure he was like i feel the need for acceleration 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 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 anyhow i just put i'm just putting all this out there in case you didn't know 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 the car into a wall all right just take his word for it chuck one last thing okay all right so if you're in an airplane and the airplane wants to just go left let's say right in the air put the roll down the hand on the window put his hand pilot puts his hand out all right so so in the old days the plane would turn and you would feel yourself lean 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 right that doesn't happen anymore why yep it doesn't happen anymore 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 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 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 so that you're urged to lean to the s to the right in that case is compensated by the banking of the plane itself and so but then it 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 that's why no one even if you 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 it's level 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 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 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 uh don't do that you should look at the water in your glass right now exactly do some science while you do it all right so when we come back i've got another segment here of stuff you thought you knew so chuck you you want another one of these i want another one any hints on what it might be oh yeah it's just on on heat shields oh sweet let's do it right okay all right when star talk returns we're back star talk chuck nice tweeting a chuck nice comic dude thank you sir yes we have some good stuff lately keep it going thank you all right all right so i want to talk about heat shields on aircraft okay so we all know that they exist and you know why they exist to stop phasers from penetrating the ship's hull i didn't say i that's a different kind of shield oh my heat shield damn not phaser shields oh man damn oh you don't want to hang around anymore okay ordinary heat shields okay you've always seen you've heard about it you've read about it and you know what they're for um i would guess because it gets hot so they're going to shield you from the heat okay that's not their purpose what yeah that's not that's not why they exist well that's a very deceptive name i thought about that that's right yeah that's an extremely deceptive name it implies that you're gonna get hot and burn up so you have to protect yourself from it until you put in these shields so that you don't die so why is nasa toying with my emotions like this this cause now you care because the astronauts is living fleshy things inside the capsule right okay so if it's not to stop me from burning up and dying what's it for okay so here it is ready you need heat shields because any object in orbit is going in especially low earth orbit it's going 18 000 miles an hour right okay that's right that's fast so if you do the math that's like five miles per second second eight kilometers a second all right 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 well spacecraft don't also carry fuel to slow down with no retro rockets no retroright now they do well no not really no well well it depends wait hold on when they're coming back to earth no retro rockets okay still no retro rocks still not retro rockets so but you're right it would be called retro rockets so whatever here 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 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 yeah uh like like in a ship like a uh all engines reverse you know and you see the propeller stop and goes opposite directions correct correct okay that's all you'd have to do but to carry the fuel that you're not going to use until you want to come out of orbit you that takes fuel to put the fuel that you're not burning and so we said we're not going to 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 so we they're called heat shields but you know what they are they're aerobraking it's an aerobraking system uh-huh you want this because you intentionally didn't bring fuel or breaks to slow you down so you use air to do it so what do they do here's the capsule in orbit moving 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 there's not aerodynamic at all it's it's totally not well it's it's air having that it's not going to be turbulent um it'll stability 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 are friction i know but okay what was the original source of that energy what do you mean uh it was your speed of the crash oh that's right the craft itself flying in at 18 000 thank you thank you we gotta get rid of that energy somehow 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 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 so 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 oh so they are heating up and then they're peeling away they're peeling away so the so all the heat is actually like wicking like moisture like that i'd 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 the moon crafts coming back had more heat shield layers than the other spacecraft wow that's by the way it's aerobraking that's what it is ingenious it is and it's blunt and it's low-tech and it worked every time i don't know who thought of that but that guy should have got a doughnut i'm telling you that's the part of your reward he should have got a parking space because that is says the new yorker where parker is highly valuable somebody somebody was really thinking i mean yeah yeah and it works and it and it works every time so so it's so it's i think the correct word is it ablates ablate so you're saying whisking it ablates and so and 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 that is genius 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 no no no just because you're entering an atmosphere doesn't mean you're gonna burn up right 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 when we landed on the moon moon's got no atmosphere right how do you get a soft landing there can't use a parachute can't use aerobraking they needed retro rockets got to have retro rockets yeah yep there it is mars has a thin atmosphere so that one had parachute big parachute plus retro rockets plus aerobraking all three to get the rovers on mars oh you drop a trampoline thank you well i'll bring that up at the next nasa meeting okay chuck knight says trampoline why did it take us five days to land on the moon [Laughter] 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 into some other form and then get whisked away as you said so you should i think you should always think of heat shields as aerobraking systems rather than oh you need this otherwise you'll burn up no you need it otherwise you'll crash that's so cool and that's really cool oh and uh in the movie 2010 ostensibly the sequel to 2001 they came to jupiter and they aerobraked around jupiter they had some really good uh visual effects for the day and to sh and they're inside the craft they're saying oh wow this is uh i wish i could see this from the outside this aerobraking basically any spacecraft with heat shields coming through an atmosphere is error-breaking any time 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 their spacecraft they come into mars and their orbit is highly elongated that's a hot uh 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 i like that that's cool so there you go chuck uh think of it as um error breaking not heat shields for the future 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 and if you fall out of your spaceship and and fall towards a planet uh if you die it won't have to be because you burned up right it'd just be because you hit the planet way that dude was going to die [Laughter] this was yet another episode of stuff we thought you should know whether or not you did [Laughter] all right chuck chuck co-host always a pleasure all right neil degrasse tyson as always keep looking up [Music] you

Channel: StarTalk

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Keywords: startalk, star talk, startalk radio, neil degrasse tyson, neil tyson, science, space, astrophysics, astronomy, podcast, space podcast, science podcast, astronomy podcast, niel degrasse tyson, physics

Id: fSNg2pKtE68

Length: 41min 25sec (2485 seconds)

Published: Thu Nov 04 2021