hey smart people Joe here you know what I freakin love cereal you know what I hate the cereal at the bottom of the box ever notice how by the time you get to the bottom you're left with this it's just little crumbs and boring stuff the dregs if you will the tastiest big bites are gone but that doesn't really make sense if cereal is mixed in the Box well it shouldn't it stay that way or if anything why doesn't the bigger heavier stuff sink to the bottom watch what happens when I shake up this bag when I pour the cereal out there's more delicious bits in the first bowls from the top of the bag why does this happen well the answer is science well technically that's the answer to everything but especially this okay back to why does this happen well it's curious that the heavier bits rise to the top instead of falling to the bottom well the same thing happens with granola and nuts shaking a can of mixed nuts doesn't actually mix them up it unmix --is them and big nuts like Brazil nuts always rise to the top that's why this strange phenomenon is commonly called the Brazil nut effect though I don't really like Brazil nuts and I love raisin bran so I'm renaming it the raisin bran effect and it's powered by physics when we shake something up we expect it to get more random but for many mixtures that isn't what happens shaking them actually makes them less random a scientist started digging into this strange phenomenon in the late 80s and how it works still kind of driving them nuts the key ingredient is motion to make particles move we have to accelerate them and for these particles that means accelerating them enough that they over come gravity they bounce or jump and that allows them to rearrange well there are a couple of different mechanisms going on here one is called granular convection granular means it's made up of small grains or particles and moving by convection a sort of rolling flow in a container as things get vibrated and jostle around the friction between the grains and the sidewalls draws particles and near the edges down particles near the center are pushed up and we get convection swirls even if there's a big dense object in the mix it gets shoveled up to the middle by the convection currents and it stays there that's right I said sugar the new Scottish word that I learned that means to shake and it's awesome but there's another way that this sorting can happen besides convection it's called percolation basically small particles fall into the cracks left by their bouncing neighbors and as they fill in those spaces the bigger particles get pushed towards the top think of it like a ball bouncing on a platform that levels up every time that ball jumps we can see this in a really cool way with some sand some salt and this thing I built watch what happens when I pour it through this little hole see that they separate if we look closely we can see that when the different grains impact they're still pretty mixed but as they settle the layers start building larger grains quickly roll down the hill but the smaller grains gets stuck in cracks along the way as the small stuff fills in empty spaces large particles roll along on top of it this process repeats and that gives us those nicely stratified of layers okay so this is cool and all but do percolating particles and granular convection actually matter in the real world well it does if you're caught in an avalanche avalanche air bags inflate around a person tumbling and being buried by snow they don't float you up the way a life jacket floats you in water they basically turn you into a human Brazil nut a big particle rising in a mix of smaller snow physics can save lives who knew well actually a car airbags seatbelts ejection seats bulletproof vests MRIs I guess that's not really news anyways even rocks in riverbeds separate this way the larger ones on top and it shows up in space it's one explanation for large boulders on the surface of asteroids that have no other business being their best part you can try this at home shake a bowl of popcorn to get the biggest luckiest kernels up to the top it even works with a bowl of chips in fact I want to know where you find this effect send me a video the next time you see the Brazil nut effect I mean the Raisin Bran effect in action stay curious and good for you till we've got a few people to thank for today's video first off I want to give a big shout out to the channel fvf fluid dynamics there's a video about this stuff over there that inspired a lot of my questions and the call was a huge help and putting together this video she's got a ton of awesome fluid dynamics videos over there an FDF fluid dynamics that you should check out what does the F stand for it stands for fun also want to tell you about another show in the PBS Digital Studios family called origin of everything where Danielle takes a look at the historical origins of everything which are sometimes a little bit weird they've got videos about stuff like why we eat breakfast the way we do and why don't we eat popcorn when we go to the movies two things which are suddenly very relevant after today's video and finally I want to say a big thank you to curiosity stream for supporting PBS Digital Studios and it's ok to be smart curiosity stream is a subscription streaming video service that offers documentaries and nonfiction titles from a variety of filmmakers and their collection features a bunch of curiosity stream originals like curiosity streams original three-part series called the age of big cats it profiles the seven major species of big cats that are alive today in a unique way that tells you the story of how they survived with plenty of sweet night-vision footage of big cats doing big cat stuff you can learn more at curiosity stream dot-com slash smart and use the code smart during the signup process