Neil deGrasse Tyson Explains Why Ice Floats

[Music] chuck we're back yes we are and this was interesting there are certain things that we just experience in our lives and never even think to question it true because it's in our everyday life and and and and some things you don't want to know the answers that's different some things are just that's left unexplained unknown i'm not i'm not gonna mess with not gonna go there no no this one you ask a simple question why does ice float right have you ever asked that i have you have okay i have yeah i mean because when you think about it it's water but you're putting it in water yeah liquid it's water liquid in water right it's water and water so and usually when you cool something down it shrinks okay it becomes more dense tell me about it so it becomes more dense and so you would think that a cooler version of some liquid would be you know if you shrink the same mass down to a smaller volume it's more dense that right all ice cubes would sink to the bottom of your glass as a matter of fact in certain parts of the oceans i'm gonna where you have what they call um oh god now i forget the name of it it just it was just on the tip of my tongue but the coldest water stays at the bottom of the ocean yeah we're not there yet oh we're actually going to talk about that yes oh sweet oh my gosh we're totally going there okay forget about that okay all right all right so so a peculiar thing happens to water when it changes state okay a change of state means you go from liquid to solid solid to gas get so we have water and there it is when it freezes the water molecule in order to freeze takes up more volume than does the water molecule in a liquid state so the water expands by about 10 percent nice okay and roughly you can think about that as if you are if you expand 10 and you go back into your liquid you will bob with about 10 of your volume above the water okay and 90 below so just put put an ice cube in your glass it's easier to see this if it's in a cube shape rather than in those crescent shapes or other things but if you take a cube and put it in there ten percent will be above the water and ninety percent will be below all right hold on oh okay all right okay okay all right i just happen to have a glass of water here oh you do and are you is your ice in it are they cubes oh my goodness look at that that's awesome yes this is a cube okay okay and you just see it's got like a little surface you can't see it but it's got a little surface because the top part is clear i don't know why but it's just like you said it's like it's bobbing up yeah it's stopping but most of it is below yeah so check a little bit about it's not happening because i said so it's happening because this is how the universe works no no you're a wizard stop lying now here's an interesting fact if you take that same glass of water with that one ice cube in it and fill it as much as you possibly can so that not another drop can go in it without spilling over the edge right if you do that okay the ice will be sitting above that level above the lip of the glass right and you might be worried oh my gosh i better get a coaster because when this melts it's going to overflow but no when it melts it's going to take up the volume that it's already displacing in the water itself and it's not going to get any higher than it currently is right this is why the arctic ice sheets in the arctic so where santa claus is right it is ice that is floating on the water in the future where global warming melts the entire northern cap when that happens it will not that alone will not increase the sea levels of the world because the ice is already floating in the bathtub of that water that's correct so the ice you need to worry about is the ice that's on land oh that runoff the runoff okay that ice you melt that you're directly adding watercolor that's on greenland and primarily greenland and antarctica so that then starts flooding the oceans and raising raising the sea levels okay so but by the way uh 232 feet if that were to happen oh thank you for that number yeah i think i tweeted once that if you if you do that then the water level will go up to the left elbow of the statue of liberty yeah the one that's holding uh i think it's the declaration of independence just in her arm and yeah and that basically you lose manhattan and basically every other coastal city of which where you find most of the great cities of the world are on the water's edge so anyhow so so so that's why ice floats but there's more going on here you could delay the freezing of the ice it freezes at 32 degrees or zero degrees celsius you can make it freeze at like one degree below zero if you put it under pressure okay yeah and it's good so it gets colder and it says i want to freeze i have to get bigger i have to get bigger i'm not letting you so then it doesn't it doesn't change the state okay but if you keep taking the temperature lower and lower under pressure the isis says the ice says okay and i will expand no matter what you're doing and boom pipes break yeah okay so i don't know why i'm hap i don't know why i'm so happy i'm a homeowner what am i talking about that's disastrous you're happy that you you now understand the full dynamics of that so it would be very hard for ice at 32 degrees to break a pipe because the pipes are made of typically they're made of copper or some strong metal and so it'll keep it squeezed down and say no you're not freezing at 30 no you're not going to let you freeze at 30 degrees no not at 29. oh 25 degrees and it and it is stronger than the pipes and you just break the pipes and by the way at that moment all the pipes are frozen there's no leakage when do you have leakage when the temperature goes up again and then the ice melts out of the path and then the water flies ugh so the the the act of broken pipes in most cases is not the moment where you get the leak because the ice is there the ice is there plugging the pipes it's later on when the ice moves out of the way so so this is the power of freezing ice now last point i want to make is well how about the density of water just as water does it change density yes it does okay as you cool water it takes up slightly less and less volume hardly noticeable if you're just swimming in it or just looking just like and if you heat water it takes up slightly more volume and a lot of the increased sea level rise in the future of global warming is simply because the oceans are warmer and they're warmer they they take up you know let's say it's one percent more depth right but you come but what is one percent more depth in the middle of the ocean where it's three miles deep okay if it's one percent more depth by the time you get to the shoreline you have flooding right okay so let's cool the water it gets colder and colder and colder it begins to shrink well at some point that has to turn around because eventually it's going to become ice where it's bigger there is a point where ice is at its densest and it's three degrees celsius really okay so you so you cool water at the surface it's denser than the water below it and so that cool water drops and it goes to the bottom okay and it stays there you keep trying to cool water at the top and it goes down to the bottom but what happens now you're cooling water now the water is 2 degrees celsius or 1 degree celsius it begins to stay on top then it hits 0 degrees celsius it freezes on top on top keeping the three degree water at the bottom right preserving all aquatic life over the winter time that's why you don't have bird's eye frozen fish once the uh once the lake freezes just like the lake if ice sank oh my gosh you would freeze lakes from the bottom up you through that top layer would go to the bottom and slowly but surely all the fish would be swimming in an ever thinner layer of water until you just go and scoop them all up and that's the last fish that would ever exist in that lake oh what a what a bear's dream no they're hibernating they're missing this that's true yeah so so this feature of water protects life over the winter aquatic life over the winter wow and once you form the ice layer on the top it actually insulates the bottom you get really cold on top but that does that how long will that take to transmit through a thick layer of ice it takes a long time by then it's daytime compared to night or spring has come and so you rarely if ever do you end up freezing an entire lake and it's because of this property of water that ice floats the ice is less dense than water that is amazing and it's it's pretty cool that this this becomes like its own little closed ecosystem where the ice freezes on top insulates the water beneath it so that all the life is protected it's protected that's amazing it's basically it so this is a feature of this fact about water the water molecule one other thing it's what enables you to ice skate okay because the reverse is true so i if i have an ice cube and it's sitting at let's say 30 degrees okay right and it's frozen so minus one let's say celsius if i squeeze it if i squeeze it under pressure i'm trying to put it into a smaller volume ice won't let you do that right but if i press it really hard what's the only way the ice can respond to you to go into a smaller volume it's got to become water it's got to become water so you can squeeze melt something even at subfreezing oh my god that's that's how you get the great ice cube there no ice spheres for drinking scotch what you just said they take a copper press and i'm too excited about this i'm sorry this is this bar information that you're sharing i know i know now what's up now we're talking about scotch and drinking i'm like oh my god uh and you don't even have your scotch voice today right now exactly yeah exactly yeah you want another definitely need a little scotch that's what i'm saying when you're skating on ice okay the blade is the way it's it's sharpened is it has a very sharp edge on one side and on the other on the left and on the right hand side so you go on an edge and skaters know about this on your inside edge or on the outside edge that is a lot of pressure we got to do a whole other explainer video on force and pressure but that pressure is so high that it actually melts the ice in place and the skate glides on a bead of water wow that's great that's why that's why ice is slippery on ice skates yeah so so yeah i mean that same premise you just um um um demonstrate it when you get a they make spheres of ice for drinking i love ice spheres yeah ice spheres and they use for some reason copper i don't know why but they used copper or brass one or the other and they just put the ice in the sphere and they let the brass it's a big weight it's a brass weight or a copper weight and it just presses down on the ice and then the ice melts into a ball that is so cool oh okay all right so they take okay so to shaping the sphere from the pressure on a shape that's not a sphere that's right okay yeah so under pressure yes it will melt under pressure it melts yet yet when you relieve the pressure it freezes instantly it freezes right because it's because it's the it's the below freezing temperature that you started with exactly and then you just have a bit a literal ball of ice okay chuck i don't go to many bars i've never seen this i trust that in your bar hopping this is something feature okay i'm gonna have to i'm gonna have to get you out man i gotta get more off i'm gonna have to get you out of the house all right so that's that's it chuck that's uh ice is less dense than water nice i'm always fascinated how we end up in these great places from something so seemingly um mundane as a cube of ice or ice melting and next time we do this we got to do this with one of your spheres of ice and i want to do a whole explainer video with you and your scotch voice oh absolutely not a problem no i don't i'll start on it right now right now all right chuck always good to have you always a pleasure neil degrasse tyson here for star talk keep looking up 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, chuck nice, why ice floats, why ice floats on water, arctic ice sheets, freezing ice, density of water explained, ice cubes

Id: cF7p5nAPnDU

Length: 14min 23sec (863 seconds)

Published: Tue Nov 10 2020