Hey welcome back to science class with me mark Rober, so today we're just gon na jump right into it class we're gon na answer. This question does farting make you weigh less, and I asked you guys this question. 70 % of the people got it wrong. So I think we're gon na update some mentals models of the world today, which is our goal, we're not about memorizing facts.

I want to give you guys principles that helps you understand the physical world around you. So if you're new here, the format is Monday Wednesday, Friday 1:00 p.m. Pacific yeah, we start with the question we get three clues. We try to unravel what the answer is by the end of class, and last time was my first one.

Everyone was really nice. I got some very good feedback where this is kind of rough. You should see the set looks a little bit better this time. Last time, like the set, this desk was still wet, with cement from having being painted, but we're figuring this out and yeah.

My dream job is to be a high school physics teacher, I'm getting my credentials right now, so they won't. Let me teach yet so life pro tip. If you want to do something, don't do it for the first time in front of 1.4 million people, but uh coronavirus here we are, it is what it is and it was fantastic. I'm gon na talk more about that.

Later and about facing your fears up to the music on and stuff once we're done with all the science, so the format here about 15 minutes for the science and then officially class would be dismissed and then we'll do a Q & A at the end. It's more interactive than a normal video, so go ahead and ask questions if you want and then I'll answer a few of them at the end in five minutes, and they give you questions about the lesson or even questions about me. I don't do this very much kind of interacting. So if you have personal questions, anything is on the table.

I just want to answer the ones. I don't answer so there's that okay, so to answer the question just farting make you way less. Let's start with another question, which is: why does some stuff float while other stuff sinks, so the hammer sunk, but then this wooden block floated - and that brings us to clue number one which is talking about this concept of density. So density is defined by how much you weigh versus how much space you take up right and I know you're a physics student, your life away, it's actually mass difference.

We mass and weight we'll get to that in another lesson. For now all the formulas work everything works. We just consider this weight. So how much you weigh relative to how much space you take up.

That's density so, if you're less dense than the fluid that you're in group, you're gon na float, if you're more dense than the fluid that you're in you're gon na sink all right. So I've got a hunk of metal here and what's gon na happen, it sinks and you're like big whoop mark metal sinks, mind blown right. I could tell you're not impressed so all right hotshot. I want you to think how can I is a brainteaser.

If I add more metal to that metal, how can I make it float? All I'm gon na do is add more metal to this another hunk of metal. Here, how can I make it float you get the answer right now, I'll be super impressed. Put it in the comments. Tell the person you're next to okay, you lose a few more points, the longer it takes you, but I'm gon na start doing this.

Okay, you're thinking, how can I add more metal to make this thing float? You figured it out yet, okay, what am I doing here, metal metal it now floats. I basically made a boat which allows us to create an alternative ending to Titanic. This is Jack. I had to make him a little more modest because he didn't have pants on this morning.

That's a duct-tape, kilt, okay, how the king of the world is rose Jack? Why are you wearing a skirt? It's not a skirt! It's a kilt! Okay! It floats look at that and it floats so much. I bet we could even add more we're. Gon na add a. I don't know this mango, it's still floating, there's an avocado, the Titanic.

Never let go there. It goes all right now it eventually sunk, but it could support a lot of weight. I know I just lost half the stream because they're like what the heck can you do. It mark you've lost your mind, but let's just talk about boats for a second like what the heck, what some of the boat boats have like you know, cruise lines have like gyms and pools on them, they're made of steel.

How do those things float? Well, the key okay density. Clearly, somehow they have to be less dense than water, otherwise they wouldn't float. We add up all the weight, the pools and the tracks and the water slides and the steel relative to how much space it takes up. If you average that out, it is less dense than water because think about all the open air and that's their trick.

Sure they've got a steel hull, but they've got so much air in the middle and when you average that out, it actually is less dense than water and it's closer to just wood right, a massive boat, basically as the equivalent density of a block of wood. So a really cool trick you could do here too. Is I've got this tennis ball here you can see. The water line is about halfway up.

The tennis ball tells you that this ball is about half as dense as waters. The water is twice as dense. If the waterline went up like 90 % on the ball, then you would know that the tennis ball is almost as dense as water, but it's 90 % as dense right. That's a cool trick.

Also. I want to show you this. If I put this tennis ball at the bottom, of course, it floats we're gon na come back to that a little bit later. That's really there's a real cool clue kind of tucked away in that.

So this allows you then to well. I should say this: there's a dude named Samuel, plimsoll, real, smart guy engineer in like the 1800s. All these ships kept capsizing. So he did something and he's like he did.

The math calculated the density he painted this line on the ships. This is called a plimsoll line if you've seen this red line on ships. What that line means is that you're allowed to put cargo on there as soon as the water level gets to that line, you got to stop loading it up. If you put any more on there, then it is too heavy and the ship is going to sink.

So he basically did that and saved a bunch of lives, because ship people are like how how to put a few more crates of this and they would. They would stand on the scale, so it wouldn't waver quite right, but it's like dude. I don't care how you weight it. The water level is not above that you can't have this ship go because it's too dangerous.

So this provides us with a fun game. You've got a tub like this, you could fill it with water, it's called doesn't weigh more or less than water or, as David Letterman said, will it float so we could start easy styrofoam. I want you to make a guess in the comment below or maybe tell someone you're in the room with of what you think it'll float or sink styrofoam. I guess that we're starting easy flow, simple.

So it's way less dense than water right golf ball. Any golf ball golfers out there: well, no, it will sink can of beans or you guys think sink all right, get a little harder, cucumber floater sink more or less dense than water flow, but it's whoops. You can see only a little bit sticking up how about mango. This is what sunk our Titanic earlier.

We've got a sinker okay, avocado getting tricky like I said, sink or float hello, but just barely okay, four more can of Diet, Coke floater sink; it floats sinks. Dun dun dun. What would make normal coke sink and Diet Coke not sink? I don't know for sure my hypothesis would be there's like three tablespoons of sugar in coke versus Diet, Coke. So my guess is that just makes it more dense than water, peanut butter, jar.

Peen about our float or sink sink - oh, it floats, but just barely and our final one watermelon is it gon na float or sink? Oh watermelon floats ours, ours, entertainment and we'll floaters. Think, okay! Now, let's talk about that, just a little bit so think about like a fish. First of all, it's really hard to be neutrally buoyant. That means, like you notice, all of these are either on the top surface or on the bottom right floating in the middle is really hard, I'm gon na get to this later.

I have a challenge to give you guys with regards to that. How does a fish do this? How does it go up and down right? The answer is it takes advantage of this density equation. Fish are smart. They can't change their weight right, they're, not like gobbling things up right in the middle of others coming around, so they they modify this the space they take up.

They have bladders that they kind of stretch out yeah, same weight, but they're taking up more volume. What does that do makes them less stands? They go up. No, like I kind of want to go down there and check that out. What do they do? They pull that in, so they take up less space, they become more dense.

They go down right. It's very clever. This also can help your mental model. Then, what's the purpose of a lifejacket? Well, a life jacket doesn't weigh very much, but it gives you more volume more space.

So you take the average of you, including this live jacket. You are going to be less dense, which means relative to water. You're gon na float easier right. If you go into a pool and you hold your breath and you're on the top surface, you're nice too sick a stick up there, you let that go! Your volume goes down and you start to uni, and then you start to sink so this doesn't work just with water.

This is true for any liquid or any fluid and something in it. So there's a channel I like called Cody's lab, and he did this experiment with Mercury and an anvil. It doesn't seem to want to stay upright. I let it tip over this.

It's whoa look at that. The mercury that it's in well, if you remember from the tennis ball, it's floating about half way up. So it's about half as dense, because that's where the mercury line is right, not the water line, so relative densities is one way to thinking of this problem right. That's the simple way: okay, let's do a little bit different way.

This is a little bit more complex, but it allows further emphasized insight. Think of forces, okay forces you're like what's a force, that's a weird word forces like anything that acts upon you right, so think of like a tug-of-war and right now, there's the force of gravity. We all know about gravity right. I've got this gravity was acting on that pin currently on me.

There's a tug-of-war gravity's pulling me down, but what's keeping me up, the floor is pushing up with the same force tug-of-war. You know that it's a tie just like in a real tug of war, because the middle is not moving right. It's not going one way or the other. However, if I was standing on a trap door in the trap door when and it's gone guess who's all the sudden gon na win, that tug of war gravity is like you oink.

I got this and I start to move down. That's when you know someone's winning as you start to move so gravity is one force that pulls on something that's floating in water. The other force is clue number two, the buoyancy force. Well.

What is that? Don't worry about these fancy words, I'm about to say the buoyancy force is equal to the fluid surrounding fluid density times the space you take up the volume times the gravity, so I'm building up to a point. That's about to blow your mind. Think about being in a pool right, the deeper you go, the more pressure you feel right, the lower you go. Your ears feel all weird, you kind of feel compressed a little bit.

That's because you have all this water above you weighing down on you right, the deeper you are. It's like! Oh you're, really feeling it it's like being the bottom person in a dog pile, that's not where you want to be. There's a dog pile. I always try to be kind of towards the top, because you have less people above you, so there's this gradient right, the deeper you go, the more it is.

So if I'm in a pool, there's actually a little bit more force at my feet than the top. Those all cancel out and you're left with a net force kind of pushing you up. That's a buoyancy force that will happen anytime. There's a pressure gradient, so more pressure at the bottom versus the top right.

So this density force. This is you or the buoyancy force. I mean if the buoyancy force is less than the force of gravity. That's supposed to be an arrow, then you're going to sink.

That's what happens with the can of beans, for the can of beans. Gravity wins that tug-of-war. The canopy's goes down because the buoyancy force isn't enough to keep it up. However, if the force due to buoyancy is greater and the force due to gravity who wins that tug-of-war, the buoyancy force does and that's what happening with the diet, coke or this piece of styrofoam.

The buoyancy force is greater, it wins the tug-of-war and it floats. So here's the big moment: what do we talked about last time? Air is a fluid right. It's not like liquid. It's a lot less dead, but I'm basically in a fluid right now and the higher you go, there's less pressure, the lower! You are there's more pressure.

That's because there's just more air above you pushing you down just like in a swimming pool. You know this is true, because if you have a bag of chips, you go up into the mountains. It expands right. That's because there's less air pushing out on it.

If you go up in an airplane, your ears hurt that's because it's a freaking metal tube flying through the air, they're pressurizing it to try and make it better on you, but they can't it's it's a leaky, metal tube, and so you feel that difference, because the Higher up you go there's less pressure, anything that has the gradient pressure. Gradient will have a buoyancy force ready for this. So the fact that this tennis ball, when I push it down, it goes up like this right. That is the exact same principle, brace yourself as a helium balloon going up both are in fluids.

This is just less dense. We it's like if you were a crab on the bottom of the ocean floor, and I put this tennis ball next to you. You would see it go up. We are like crabs on the bottom floor of this ocean of air.

This is so poetic and we see this balloon going up. Where's it going it's going up because it's less dense than the fluid around it right here. Air is kind of pushing it up because the gradient and it will keep rising till it gets to the surface, which is where the the density of that helium balloon is equal to the density of the atmosphere because it gets less the higher you go. Alright, so hot air balloons float because on average, if you take the basket and the people plus the hot air which is less dense, it's just less dense than this ocean of air that we're in right and it goes up.

So this leads us to the final clue, which is that fights are less dense than air. Okay. Now, technically you have all the puzzle pieces. You need this one's a little harder to connect, but technically the pieces are there.

I want you to think about those puzzle. Pieces, while I show you this final clip - that kind of summarizes everything we learned, this is from a video I did made a fluidized hot tub out of sand floats in the sand and other stuff sinks. This has to do with the buoyancy force, which is a function of the density of the surrounding fluid and the volume of the object itself whenever an object exists in a pressure gradient. There are forces from pressure pushing in on all sides, but they push a little bit harder, the deeper that you are, which is why it hurts more to be the bottom guy in a dog pile or it hurts your ears more.

The deeper you dive in the pool - and this makes sense because the deeper you dive, the more water there. It's above you pushing down and if you add up the size and direction of all those arrows, a bunch of stuff cancels out and you're left with one net force, pointing outwards. That is the buoyancy force and if your buoyancy force happens to be greater than your force from gravity you float and if your buoyancy force happens to be less than the force from gravity you sink now. We usually think of buoyancy with water, but you can think of things like helium balloons being buoyant in our atmosphere.

So here's a trick question which of these has a higher buoyancy force. It's actually the rubber ball point see. Force has nothing to do with the density of the object, just the volume. So since the rubber ball takes up more space, it has a higher buoyancy force, but you might object.

Then why does the rubber ball sink and the balloon floats? Remember it's a tug of war, the rubber ball sinks, because the force from gravity on the thick rubber, skin and the air inside is bigger than the buoyancy force, but for the balloon, even though it doesn't have as big of a buoyancy force compared to the ball. It still floats up because that buoyancy force is bigger than the weight arrow from the helium and the thin rubber shell and the helium will keep rising like a ball floating up from deep in a lake, and then it will eventually hang out where the density, the Atmosphere is roughly equal to the density of the helium in the balloon, because that's where the tug of war becomes equal, we made it through now, back to my nephews, that's my nephew. Beckham he's watching right now, hello, backup! I love you. It's a tough love that was tough love.

That's possibly my favorite clip of any clip I've ever made on YouTube. He was fine, even though it was like sand eventually, so we're gon na answer this. Now we got all the puzzle pieces. First, I'm gon na give you the grade-school answer.

Someone gave me this suggestion and breaking it down into different levels, so the grade-school answer is, if I step on this scale and I'm holding these balloons, which are less dense than the air around me right now. If you take my average density, it's kind of like wearing a life jacket, what do you think happens to my weight on the scale? Well, let's say I had 5000 balloons, fun fact at about five thousand balloons, someone like me would float kind of like the movie up the more helium balloons, I'm holding the less. That scale is going to read. Conversely, I have this heavy weight here and more weight.

I'm holding this this is more dense than the air around me. That scale is gon na read more well, that's scary. To see that number wait, that's not right! Okay, I weigh more okay. Well, we know from clue three farts are less dense than air, and so the answer to does fartie make you a list, ladies and gentlemen, because farts are less dense than air.

It's like you're holding a little fart and you poof, let it go, and because of that, that scale is going to read a little bit more right. So farting makes you heavier so eat a lot of beans to temporarily have that gas in you. It's a great weight loss program. I guess right farting makes you heavier and that's the grade-school answer.

The junior high answer middle school I'd say after farting on average you're a little bit more dense right because you were holding that little helium balloon of fart and so more dense. Things weigh down more in this ocean of air that we're in so you're gon na weigh a little bit more. The college answer is kind of look at the tug of war between buoyancy and gravity and if you look at the Delta V volume of the little fart you let out multiplied by the density. The air around you.

That's like buoyancy, x' participation, the volume of error times the density of the gas inside you on that tug-of-war buoyancy gives up more, so gravity wins a little bit more you're gon na weigh a little bit more okay. My favorite answer, though, is the grade-school one right. Farting weighs less than air, so it's kind of like you're holding some helium balloons. You let go you're gon na weigh more.

Did you catch that? Did you get the wireless transfer of knowledge from my brain through that camera in your phone ears? This is magic. This is science people. This is good stuff. This honestly gets me stoked and pumped I love these aha moments.

I love giving them to other people. Hopefully you had one, you can rewatch it if you didn't so. The winning answers submitted by someone was la la see. You I suck at names, you guys have some hard name to pronounce.

He says farts are mostly methane, which is lighter than air, so fart is like a helium leaking from a balloon. I like that, it's very concise and simple, so I'm gon na start something new. I have a challenge for you, guys cave all, want you to get a tub like this and play. Will it float with your family or just with yourself whatever, and try and find some tricky objects, see if you guys can keep score and trick each other, then what I want you to do is try and make something neutrally buoyant.

So you could take this block of wood and you could take some washers or coins to it. Try and get it to be neutrally buoyant like a fish, it's really hard. So if you get a good combination, send it to me on either Twitter or Instagram or Facebook and I'll pick my favorite one and show it next time the one that can last the longest, even if you get three or four seconds. That's pretty good trust me.

This isn't that easy, okay, we're gon na get to Friday's question, but first I'm gon na do a little moment, so is where I turn on the music and have a little moment right. This feels like you're and I'm a marker over video. Now I want to talk to you guys just for two minutes about fear of failure, so I decided to do a livestream for the first time in front of a bunch of people and it wasn't super smooth, but I kind of loved that right. I love this opportunity to try and master something and to learn, and do it a little bit better next time and that can be scary, but that's also how you learn.

It's like one of life's best treasures. It's having these opportunities. I gave a TED talk about this called a super Mario effect, and it's basically when you play a video game and you fall into the first pit. Let's say Super Mario Brothers you're not like.

Oh, I fell in the pit, I'm so ashamed. I never want to do that again. I failed right, no you're, like oh shoot. I fell in that pit.

Okay. Next time I come a little bit higher. I got ta jump a little bit more coming up with more speed. People were like hey Mark great livestream.

Do you want some feedback, I'm like hey the sidewalk feedback, that's like playing Super Mario Brothers in one level through two and you're like dude, I know how to get infinite. You know extra minute and I'd be like I don't tell me. I guess I want to know: I want to get better it and master this a lot of times with our life challenges. We say I just don't want to try that, because I might fail - and that's embarrassing to me right.

So if you treat your life's challenges like we treat video games and focus on like beating the game versus focusing on that, I might fail, you could be more successful and have more fun and learn a lot more. So this is me punching coronavirus in the face and just trying something and if you think oh but mark you're, just a natural of this no go watch my first youtube video. I will link it in the document below where you can also guess on next week's question: it's bad. You can see my improvement and I giving this gift to you guys of watching me and proving something.

So I can be good enough to teach physics in the classroom. You guys are helping me hone this in right. Alright, so go watch that TED talk. If you need some inspiration.

Cuz you're, like I got a punch coronavirus in the face, but I'm afraid I don't know what to do. Maybe that gon na help you push you over the edge question for next time. Here we go internet, I'm known as the space gal and mark. I was hoping to get back down to the basics, so I had a question for you: why is this bad blow? Alright, that's my friend Emily! She actually has a Netflix show coming out this summer, where she kind of does experiments around the house.

In fact, right now, she's live-streaming, every day on Instagram, I will link her YouTube. Video. If you want to cool, do cool experiments in your house that you could do which is junk. You have lying around your house go check out.

Her channel she's got some really cool stuff. She's awesome, she's, a great science communicator. So why is the sky blue? We're keeping it simple? Alright, that's next week, and maybe you kind of know that has something with frequency. I'm gon na give you a way to remember that a mental model that's easier than just like memorizing equations, because that's how we roll here, alright so officially class, is dismissed, link for guessing how that works and other links from stuff.

I talked about like Cody's. Video will be in the youtube description, so you can check that out. I'm gon na take the last five minutes to answer questions. I see that I'm Way over time again, there's just too much cool science.

I can't help it I'm sorry. I really need to make these shorter. I'm trying bear with me here. We go so you're free to leave classes officially dismissed I'll.

Just take the last five minutes answer some question: what is with the watermelon theme on this channel? I just love watermelons they're, beautiful they're. Just cool they look great when you explode them good question: what did you get your college degree in? I did my undergrad at BYU and mechanical engineering. I did grad school at USC while I was working at in mechanical engineering. So I'm a mechanical engineer.

A lot of the stuff I do on my channel is kind of like a mechanical engineer II and pppp pppp. When did you decided you want to be a you teacher? I just I honestly. I crave that feeling myself of having those aha moments of like having a mental model heirs of fluid, and that helps me understand everything around me when I was in high school physics it something just clicked for me and I was like: oh, you can explain the World around you with math and equations, and I craved that I loved, I craved the feeling of giving that like gift to other people, so that makes me want to teach I want to do in the classroom, because you get a little bit more of that personal Feedback people like, oh, you could reach a lot more people through youtube. I mean it's true, but like I'm talking to a camera right now in a room with two people right in a room by the way that has a couple of really cool robots for world records that we're currently working on.

I would turn the camera, but I don't want to give anything away. You guys might steal my ideas so yeah I kind of want to do in the classroom. So I get like that selfishly kind of get that feedback. I get to see the eyes light up.

I know it kind of happens sometimes here there's something about seeing it in real life. Do one more question: okay from all the questions like picker so hard to pronounce mister Hughton. What does the pathway which took you in order to get to NASA? When did you start planning I'll just say real briefly, and I on this note, if you don't know exactly what you want to be when you grow up, that's okay, when adults are like, what's your 20 year plan, it's like I don't know, nobody knows my philosophy On this, it's like crossing a river. If you see a stone in front of you, you kind of step on it and then once you're on that one, you kind of wiggle a few more stones.

With your toes and it's like, oh, that one's the most stable. I like that one, I'm gon na jump on that one right, the key is just to dominate at every level. You are just do your best, try your hardest, SuperMario effect and then that will just open more pathways for you, I got lucky. I put my resume literally in a stack of resumes and they happen to pick mine.

It was like excellent timing. So for me to tell you oh, this is how you get to NASA cuz. Oh I did it would be like hey. I won the lotto the trick for picking the winning lotto numbers is like choose your cousin's birthdays right.

It's like just my philosophy, would just be like just dominate wherever you're at. If you're in high school. Try your hardest, the harder you try, the more you learn. The more opportunities you have, if you want to paint paint like crazy paint, a ton and then you'll get better and then you'll have more opportunities and it will lead to other the other cool things and it's just a fulfilling way to live life.

So that's it class is officially dismissed, I'll, get the outro music and we'll see you guys next time, and my guy, who is supposed to bring in the thing at the end is a little slow.