Neil deGrasse Tyson Explains Wind Chill Factor and More

[Music] chuck what's up neil we're back yes we are time time for some more knowledge that you didn't think you needed is that a positive thing or is that yeah i don't know i've been thinking about it that's a very good thing it's always good to have knowledge that you didn't think you need because then you realize wow i need that i need that in my life okay so you've all heard you and others for sure have heard of wind chill factor yes okay what is your understanding of wind chill factor okay so you know they stopped calling it that they now call it the real feel temperature okay that's what they call it now all the meteorologists they call it the real so they say it's uh it's uh 28 degrees uh but with the and then they say this but with the wind chill the real field temperature is 15 or more minus three gotcha gotcha okay so that's that's an accurate completely correct understanding of our concept of wind chill factor okay so i just want to explain why there is such a thing as a wind chill factor okay okay so your body has a skin temperature it's about 97 degrees or so fahrenheit so if you have just air sitting above your skin okay your your skin is 97 degrees around there plus or minus and air is typically cooler than that unless you live in like texas right someplace where it's always very very hot and i'll get back to that in a minute but usually the air is cooler than your skin so now they worry because if the temperature gets very cold out watch what happens you you go out expose some skin and let's say it's 32 degrees you'll feel cold fine and that's the air above your skin is removing heat from your skin that's why you feel cold something is taking heat away from you and it's the air the air sitting above your skin will be systematically drawing heat away from your body okay if your body is losing heat you will feel cold where it's having you lose heat okay that makes sense it makes sense right so the air is taking heat away but the air is just sort of sitting there doing that right the 32 degree air by the way that's why i don't wear chaps in the winter time but go ahead okay that's why good reason among others i would suspect okay so now watch what happens if there is a breeze then the air that had just pulled heat out of you is now swapped with fresh 32 degree air oh oh okay so previously the heat that came out of your body warmed the air above it right just a little bit just a little bit so what that feels like is what we say 32 degree air feels like right it's the combination of this now a breeze comes wind comes and that air gets shifted off fresh cold air comes in and now that's taking heat out okay so it's if this keeps up the air is pulling heat out of your body at the same rate that colder air would be taking it out of your body if it was stationary wow so you do that calculation and you find out and i don't have the the tables in front of me so let's make up some numbers that can be you know sensible for this example by the way that's my favorite kind of science makeup numbers i'm not you i just make it up yeah you can check this out on table i don't have it like stuck in my head but what you can say is air at a certain speed growing up let's say 10 miles per hour across my skin at 32 degrees is like air at 23 degrees that's not perfectly still that's perfectly still exactly that is by the way okay full disclosure now i thought this was not even going to be that interesting this is really interesting i mean this is really cool because it makes so much sense see i told you it's knowledge you didn't even know you needed but go ahead continue i'm fascinated okay so now now just while we're there yeah and this wasn't really the subject of this conversation but we're there so i'm going to throw it in well you got me now um air is much less dense than water okay obviously right okay all right much less dense by like a factor of a thousand or multiple high hundreds okay i forgot the number but you can do the math if you compare the densities there's a factor there okay so that means when you're touching air many fewer molecules are interacting with your skin right than if you if it was water touching right if i have a mixture of water and ice right that will be 32 degrees okay it just will be that's how that works out yes if i plunge your hand into that and keep your other hand out in the air at 32 degrees your hand in the water and the icy water will freeze faster than your hand and the air will i i that's i guess what i knew you were going to say that but this is the first time that it actually made sense to me it made sense because many more molecules are touching you to take this to suck the heat out of your body so you have more molecules on the surface of your skin to actually pull away the heat that's so cool correct and that is why you just explained something to me that i've always accepted always understood to be true never really questioned it because it's just it's one of those things that you just know that happens when you want to make something cold you have a can of beer or soda or a bottle you don't just stick it in ice you stick it in icy water or water that is bet better than icy water you put it in icy water that's somehow moving and it will get colder so much quicker correct so in other words you can put a a your champagne in the refrigerator where it's only touching air or put it in an ice bucket where if it's only just touching solid ice but there's still air between the solid ice add water to it now you have fruit you have 32 degree water and by the way if you want to get it even colder than that you put salt on the ice it melts the ice at the temperature the ice is so the ice could be 20 to 25 degrees it'll melt the ice at 25 degrees you have 25 degree water and now you put it in and you you jiggle it as you do right like that yes and then you're you're you're basically creating a a liquid cool chill factor so okay but it's also why if i can send you out butt naked into 35 degree air okay you could run around for a while now you can even pump some energy it'll be cold and uncomfortable right but we'll find you alive at two hours later no you'll find me dead of embarrassment okay that's what you'll find me i throw you into 35 degree water right you're you're you're you're comatose in 15 minutes yeah you're done you're done right yeah okay it's the same temperature it's a matter of who's pulling heat away from you the most effectively that's amazing great so that's the foundation here but that's not the point of this conversation oh what that was not where we're headed we're not excited oh my god this i feel like i'm in a ron popeil infomercial for physics but wait there's more wait order now order now you'll also receive okay here we go you ready what's the bonus okay so let's raise the temperature some more let's make it um 85 degrees let's make it 90 degrees outside all right it's 90 degrees okay that's still cooler than your skin temperature okay it's still cooler all right so you'll feel that amount of heat i'm a little uncomfortable i whatever but the air is still pulling heat out of your body right okay but not but but you you know what 90 degrees should feel like when you walk out there okay right so watch what happens now a breeze comes so whatever rate 90 degree air was taking heat out of your body right it will now take heat out of your body faster because a fresh pocket for the same reason we're talking about wind chill factory except we don't call it wind chill factor in the summertime we call it a cool breeze we call it refreshing we call it a cool breeze but that air is the same temperature as the air that was there before you had the breeze right so it's not the breeze is not cooler not at all no the breeze isn't cool i am baby [Laughter] so our vocabulary changes from wind chill factor to cool breeze right but it's still it's still a chill factor it's still making you cooler yeah that's great it's the same temperature air coming across your your body right the same temperature air okay yeah except the problem with that though is that weathermen will feel like dumbasses when they go you know and we're looking at a high of 97 with a wind chill of 93. exactly that would be perfectly legitimate right okay nothing wrong there right okay so and while we're there let me add this there are two ways you can feel hot one of them is you're not losing heat as quickly as you should okay another one is you're directly receiving radiant energy from the sun okay directly so photons moving through the atmosphere and impinging on you right this is enhanced if you wear dark clothing okay dark clothing absorbs all the sunlight right white clothing reflects most of it right okay i have a skin suit of dark clothing there you go right so that's why the clothing colors would generally changes from summer to winter right okay you want to stay cooler in the winter warmer in the summer you wear lighter clothes in the summer reflecting this radiant energy that's trying to get in your body and vice versa in the winter so now watch let's say you're out on a at a baseball game and no it's a little league game and you're there and you're out in the bleachers and it's hot and you say i gotta go where it's cool so you get up and you go under a tree in the shade in the shade okay the air in the shade is not necessarily and is hardly ever cooler than the air that's out in sunlight right because air mixes very very definitely there you go okay but you say it's cooler because what you have done is subtracted away the radiant heat hitting you from the sun right that radiant heat is not participating in the temperature of the air the air is transparent to the radiant heat it's why you can see the sun in the daytime okay air is transparent to sunlight so going under the tree the air is the same temperature you're subtracting away a source of heat that is the sun itself right and then when a breeze comes you got it it's margarita time more creative now it's margarita time i got shade i got a cool breeze okay which is not even a cool breeze but wait there's more uh oh here we go okay all right the reason why you sweat is i've been caught [Laughter] that's different okay so if you sweat there's a bead of sweat on your body right okay now the beta sweat is about the same temperature as your skin okay the breeze blows across your sweat and across your skin your skin will feel cool that's fine but what that warm air will do to the bead of sweat is have that bead of sweat participate in taking heat out of your body because it requires heat to evaporate and your body's hotter than the air so where's it going to get the heat to do this your body okay these we're talking about cases where you're 97 degrees and the air is like low 90s okay so so the bead of sweat now says i want to evaporate i will take heat from your body to do that and to evaporate a bead of sweat takes more energy than just the energy that's pulling out of your skin from moving air gotcha that's why when you sweat and then have a breeze across you it's way cooler than if you didn't sweat you ain't lying that's fonzie cool right there but that's funny that's fonzie cool and in fact in theme parks where everybody's got to wait online they have these sort of mr misters there yes that if you're not otherwise sweating it'll put water on your on your body without you having to have sweat it there that water then evaporates and then you feel cooler that's excellent okay so your body does this to cool down more effectively all right so now here's the problem if we're almost almost all the way there if it's high humidity uh-oh sweat has a hard time evaporating right because there's no moisture in the air there's moisture in the air and it's trying to compete it's trying to get into the air where there's already moisture all right and it's a contest between who can put the moisture in the air if the moisture or the air already has moisture so you start sweating the breeze comes it has a hard time evaporating the sweat okay so the sweat just stays and you feel dank you feel hot you feel wet you are uncomfortable and so they have this they have a heat index or something it's the ability of your body to cool down under those conditions and the lower the humidity the better able your body is to accomplish this nice okay so now we're ready for the final offer okay what happens if the air temperature goes above your skin temperature oh if your air at the air temperature is a while skin temperature let me say you explode [Laughter] so watch what happens now now the air blows across your skin but the air is hotter than your skin so your skin is saying hey i want to cool you down so your skin takes heat away from the air and puts it in your body well if your skin is absorbing heat from its environment rather than giving heat to the environment you instead of feeling cold you will feel hot so we go from a wind chill factor to a wind heat factor gotcha that's why when you open an oven and the flowing air comes out you don't feel cooler from that you feel hotter have you ever been behind a jet engine when it turns on you feel hotter okay that air is hotter than your skin temperature it's a wind i've had that experience okay i don't stand behind jet engines but i'm gonna take your word for it so it's a wind heat factor that's why if the temperature goes above your skin turning on a fan no gotcha fans are bad when the temperature is above your skin chemicals because watch what happens watch what happens watch what happens when you sweat so now you sweat your butt i'm going to sweat so i can cool down the bead of sweat is there on your arm hot air blows across it and the sweat says hey i can evaporate by taking heat from that hot air so it evaporates using heat from the air instead of heat from your body heating you up even more even more not only that it's also dehydrating you oh so you are losing liquid and heating up in the presence of moving air that's hotter than your skin temperature so they have found old people in homes where if the air conditioner breaks and they put on a fan and the temperature rises they're dehydrated and they're dead from um heat uh heat exposure yeah and one of those is a real problem it's just so the whole range of what happens when air blows across your body we have different terms and different ways of thinking about it but it's the same phenomenon it's which what direction is heat going when the when you put two two surfaces or two uh media in contact with one another wow that is now this has become something that's very very useful we started out just you know learning some stuff but this is really people should really look at this especially since our summers are getting hotter and we're having more days than ever that are above 100 degrees this is really useful information now yeah yeah and so and there it is that's why in the summer you should always drink a lot of water because your body's trying to cool you down right sweet so there it is you heard it here chuck always good to have you man always a pleasure this has been star talk neil degrasse tyson here signing out as always bidding you keep flipping up

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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, StarTalk Explainer, Neil deGrasse Tyson, Chuck Nice, wind chill, temperature, breeze, air, water, liquid chill factor, cool breeze, skin temperature, air temperature, wind heat factor, chuck nice neil degrasse tyson, chuck nice stand up, neil degrasse tyson explains

Id: DvEFn8PO22M

Length: 18min 0sec (1080 seconds)

Published: Tue Aug 25 2020