Welcome back to science class, I'm your host Mark Rover, it's good to be here! It's a beautiful Monday! So today we're gon na be talking about how to waterproof your hand, and I think you can make the argument your hand actually is kind of waterproof we're talking about like how you make it. So it could come out of water dry, all right and, as usual, to answer the question. We have three clues to kind of help us get there and we use as few equations as possible and we're our goal here again is to not just memorize facts. We're about getting the right mental model because, with a mental model, you can understand the world law better and you could extrapolate and really have a good understanding of everything that's going on in physical around you.

So why are we doing this? It's coronavirus! It's two thumbs down. I wanted a ability to connect with you guys a little bit more plus. I want to be a high school physics teacher one day, so this is good practice for me. I will.

I do have an announcement. There will not be any class. This Wednesday I apologize, but the good news is, I still want to be making normal videos right, my monthly video, so I need to film for something this Wednesday so no class on Wednesday, but we will have class on Friday all right so last week, last Friday Was a little abstract with like electromagnetic waves and stuff, so today we're gon na get down to basics. Again, we've got some really cool demos that you can do at home as well as the science, I think will be pretty simple to understand.

So word is gon na get right into it with clue number one of how we're gon na do this cohesion? That's a fancy word. What the heck does cohesion mean? Let's pull in tight on this camera and I'll show ya. So I've got a paper clip here and no big surprise. When we learned last Wednesday, a paper clip is made of steel, it's more dense than water.

Of course it's gon na sink right. But what if I bent a paper clip like this and then I lowered it a little slower. It is now floating on the water and you're like what the heck mark. My life is a lie.

Everything you told me last week when we talked about buoyancy, should say those should sink right. Well, you probably know this from a common term called surface tension right, there's some surface tension on the water, that's causing it to stay up. Let me explain: what's going on there, so wait! I've got this snap, I'm here, sorry there we go okay. Now this is oxygen.

This is h2o two hydrogen's one oxygen right, so these are attracted to each other because of basically magnets positive and negative forces. Well, what happens when another water molecule comes up like this? This is negatively charged this oxygen and these white things the hydrogen they're positively charged. So what do you think happens? Well, it's like a magnet, they kind of come close and it's like hey what's up and they kind of stay close to each other and more water molecules come and it sort of forms like a magnetic net. That is what is called cohesion.

So here's a little diagram I've got here. This is like a mug of water right all these blue things are water molecules and that those black lines represent the cohesion, that's kind of like the forces in between the molecules now there's an air in this diagram see if you can find it has to do With the tug-of-war thing we talked about last week, you look at this top layer, they're being pulled down so like one take example, one in the middle - it's equally suspended all around, so it wouldn't move right. It has a tug-of-war, ropes, being pulled in all directions. It's gon na stay right where it's at.

We do look at this top layer, they're pulling side-to-side okay, so it won't move laterally, but up and down it's just being pulled down, there's nothing to pull it up. So what's gon na happen, this these molecules are neat. They're gon na win that tug-of-war and it's gon na pull that top layer down so in reality, a cup of water actually looks like this see that top layer, these things get pulled down and it sort of creates a film right where the there's more density of Water molecules, so it can support more on the top surface right forms like a skin. So let's see that in action, I've got a penny right here and I've got a question for you how many drops of water you think I could put on a penny.

Make a guess in the comments or tell someone you're with right: maybe you think it's like four or five or six: let's count these out together, all right, one: two: three: four: five: six: seven: eight nine ten oops, 11, 12, 13. 14. 15. 16.

17. 18. 19. Whoops 20.

Oh no! I kind of it's really hard all right. A lot of this is coming out. Cuz I suck at putting these drops out. But if you do this alone, what you should find is the number: what happens? Is it bubbles up like that? On top right, we did this in rehearsal because we couldn't get in tight enough, but the numbers should be somewhere around 40.

So that's what we saw when we were just doing it right before this, when I was a little bit better with putting my drops out, it creates this. It bubbles up like that right, and that makes sense, because it's like a skin, where you see it kind of pulling together on the outer surface now, animals in nature sort of know about this, and they take advantage of it. Can you think of an animal that takes advantage of this surface tension phenomenon? You got this water Strider right and these are very fascinating creatures. Maybe you've seen them.

This should look kind of familiar, unlike a pond right, see those little dimples, they're floating. What's cool look how they propel they've got two little oars with their middle legs and the other ones just keep them on top of the water. Now these guys are kind of brutal. I didn't realize it.

They'll they'll find animals that can't swim in the water coming down the stream and then they just like suck their guts out, which is uh yeah. It's that's that's nature. For you. This is amazing, but that's the circle of life.

The animals go in there, that's what they do, they find animals, I can't swim and they just have a nice juicy lunch. So here's a question for you. Let's say you were in space and you had a towel. That was really wet right and he went to wring it out now on earth.

If you did that the water comes down, what do you think would happen in space? Make a guess tell Simone: what do you think would happen? Well, we know what happens thanks to the Canadian national treasure commander, Chris Hatfield. He did this. He did this experiment check this out, so that's filled with water he's gon na squeeze it, but of course the water has that skin on the outside. That keeps it together.

Right that cohesion, it's coming up to divine the water, is all over my hands. In fact, it rings out of the cloth into my hands and if I let go of the cloth carefully, the water sort of has it sticked to my hand, you can see it. It even sticks to his hand there a little bit because again, it's like the water is like kind of like magnets right. It's that surface tension that cohesive forces want to stick together.

Okay, so what if I told you there is a way to totally destroy this cohesion and what, if I told you you've touched it today. Hopefully, I'm just gon na get right to clue number two baby. So it's magical. It does two things one of the things it does is.

It destroys the cohesion on the top surface, so I'm gon na come back here. You might have seen this before something like this. This is just a bull with some pepper. On top, I'm gon na get a little bit more, and now I'm going to take I'm just gon na dip this toothpick in this soap right, let's see what happens, it hits it and it goes all out right.

It spreads out. I have this pepper in earlier, so it didn't, it doesn't go out with like the amazing force. You should see if it's like fresh pepper in there, but you see how quickly it went out right. So, let's talk about the mental model there.

That can help us understand that a little better, these molecules are all like kind of holding hands to the top surface. Right soap comes in and be like. Ah, you guys can't hold hands, break it up right, so any any type of cohesion where these molecules are kind of attached to each other soap gets in, and it negates that and makes them like non-magnetic anymore and so think of it as like a net on The top surface I've heard people explain this as like. Oh, the the particles run away from the soap, but if you have the mental model that it's sort of like a net on this top surface again, if you have just a fresh bowl of water, this is really pronounced.

I'm gon na do it again and think of like a tight net on the top surface and it's being cut just sliced right down the middle, and then what you see here should really make sense with that right. So because they're still forces out here, you've cut this net in the middle like a bungee, cord or rubberband, and it kind of all moves to the outside, as you can sort of see there. So, knowing that take a guess at what happens here, what do you think would happen if I take another soaked toothpick and I put it at the top of this bowl with the paper clips? Well, I would guess those paper clips are gon na move away and sink. So this is a good, practical joke challenge, someone you have a bowl and they have a bowl and then in your bowl, give them soapy water, and you just have normal water and then see like whose does better so now we're gon na do another cool thing With the same principle, I've got like a little foam boat here.

Okay, I got this idea for my buddy science Bob and I've just cut the back out and what I'm gon na do. I'm gon na take this soap again. This is something you can do. This is just like foam and I'm gon na put it in this little.

I'm applying the soap to this cavity, see if you can see it on this camera. Okay, that little triangular cutout is the only surface that I'm sort of putting that soap on okay. Now, what do you think is gon na happen? If I put it in this trough right, I got a little rain gutter regatta here. Okay, let's see what happens when I stick this boat in this water, one, two: three: how cool is that we could have gone way further, what's great what's happening here.

Is you have that same principle right? Because the triangle is happening? You have this triangle and that's where it's breaking down the water, it's basically shooting out, like rubber bands out its back as it cruises along. We could've done like twice. You can totally do this yourself at home and now here's a question. If I have one that looks like this all right, you see how the cutouts at an angle.

What do you think would happen in that case? Is the boat gon na go straight? It's shooting right, and I tested this. It does it. It's really cool. If you have a bowl, you just have this thing going circles because there's a thrust vector kind of pointing out that way, so it spins around like this, and it's really cool so soak those two things: it's a one-two punch.

The first is this: like: hey you to break it up those cohesion forces, it breaks it up. That's helpful when you're washing your hands, because, instead of the water sticking together, it actually gets on your hands and it can get into the dirt and it breaks down the dirt a lot better. The second thing soap does, though, is that it breaks down fat, and this is why soap is the freakin best when it comes to coronavirus. This is a coronavirus.

It's just a shell, that's kind of like a fatty shell. It's made of fat inside you just got some DNA, that's basically what a virus is. Okay, so the soap not only will break up water pulp molecules and make you get your hand better, but it'll come and just dissolve this shell, this this fat, shell and then it just totally makes the virus like not even a thing. Oh all right, I'm gon na do something I shouldn't do.

I need this rain gutter off. It's filled with water. The EDS are kind of duct tape, so I'm just gon na cut the end and get it out of the way for the next demo. Let's see if this works Wow it's working a lot better than I anticipated it would alright, that's probably good you like come help me grab this.

This is my amazing, assisted EUI. Just take that I'm gon na walk over with you, okay, good good, okay, get out here, thanks buddy! Alright, now I've got this dish here. We're gon na demonstrate the fact that it can destroy fat. I've got some whole milk.

You need. You need to get whole milk. You can't do this with like nonfat milk, alright, so you've already showed what can do two cohesive forces now, because vitamin D has a lot of fat. I'm gon na pour this in here.

Take some cool food coloring and do this and make a cool design. Okay, let me see this okay, all right now, I'm gon na dip, two toothpicks in our soap here. What do you think is gon na happen should see some cool fireworks here. Let's see how cool is that it feels like a super power, or it's just like shoots like a plasma so again right there, it's sort of destroying that fat and getting rid of any sort of the lipids that are actually.

I can just hold this right here. Okay, so we're powering through this all right now. That brings us the clue. Number three.

Another fancy word, which is adhesion right: we've got cohesion and adhesion, and in this case let's pull this camera announced. This is sort of cohesion is when molecules stick together themselves. Adhesion is when those same molecules stick to the cup here. I threw it away right.

So you've got these molecules. Cohesion is sticking together. Adhesion is where they stick to the thing on the outside. So with adhesion, you get something like this.

You see this red paper. Towel check this out. You've probably seen this kind of concept before see how it creeps up that towel. That's adhesion happening.

That's just water. There, it's creeping up the paper towel. That's also called like capillary action and the reason this matters in nature a lot. It's really important.

A clue is on my shirt where, as capillary action happen in nature, you think big trees right. It rains there's water on the ground. How do they get that tree up? They don't have pumps, they get it up through tiny little tubes veins and it's this capillary action, the adhesions sticking to the side that allows the water to go up the tree. So that's also like the no slip condition.

If you take a fluid dynamics at the edge, you have the boundary layer, the no slip condition that's due to adhesion. So what if I told you, there was also a way to destroy adhesion right. You've probably seen this before I've got these two shoes here: okay, see, if you can guess oops how's that again switch cameras all right. So here we go so that's see how that's on the shoe see how it's starting to like seep into the shoe itself.

It runs off, but it's kind of staining check out this side. How I just this is just so cool. Look at that so what's happening. Is these shoes have a special hydrophobic coating on them, that's kind of oily and it's just not allowing those water droplets to stick to it.

That would be adhesion right, so it destroys that adhesion no matter what I try and do I can't get it wet. Unlike this side right, that's just beautiful so with something like this. When you make a hydrophobic coating on it, you solve the cohesion with that water and scene itself, but the adhesion basically goes to zero. That's because it has like microscopically, it's really rough and it kind of makes the surface oily, because water and oil don't like to mix alright, so that kind of brings us to how to make our hand waterproof.

Okay. So I've got this water here and I've got some baby powder basically and truth be told. I thought I thought this is still pretty cool. I wanted something you guys could do at home.

So if you just have some baby powder, it has to be the kind of talc. I can now stick my hand in here see how it's staying dry. You can go pretty deep with it. It's not like perfectly perfectly waterproof, but I like that.

It's just something. If you tried using flour, the water would soak up and adhere to the flower, but talc has special properties that doesn't allow to do that. Now, my buddy science Bob he he did this. He had a special powder.

Here we go. This powder is called Lycopodium powder, which is hydrophobic same principle as the talc, but you could go even deeper into the water. That's really cool right, so I have to, of course give the crown to my buddy Derek from veritasium he used aerogel, which, just with coronavirus you can to layer. This is awesome.

That is true all right, so that's a bunch of stuff that you could totally try at home to just play around with this concept of surface tension, cohesion adhesion a lot of stuff there. Hopefully that makes sense knowledge, Wireless knowledge transfer complete. So the challenge for this time again not for Wednesday but for Friday. I want to see who can put the most amount of paper clips on a surface and then have some creative way of destroying the cohesion.

So, by getting rid of the serpent ation with some soap and then I want to see them all fall down, so who could do the most and have a cool way to kind of have the cohesion go away? All right? That's the challenge, speaking of a challenge and and to submit that, by the way, just tag me on social media could be Twitter, Instagram, Facebook or tick tock. Here there was the the the submissions from last week or just freaking amazing watch this. What Cooper there at the end is cheating I mean he used watermelons he's Mario. That pot is plaintive like a tube.

He just he knew exactly what it's gon na work for me. So, like I said last time, Bo's wanted to give out like eight pairs of headphones, so he's a 700 kind of dope there. They will be reaching out to you and the next like day or so. If you were the ones one of the ones they selected again, I kind of struggle with this like intrinsic versus extrinsic rewards.

I don't I kind of want people to do this, for the sake of doing it, to learn the science and and to learn something cool, but it's cool. Sometimes, I think to offer something nice to if you can so try and do it for the right reasons. If you wouldn't headphones, so be it, but there's so much cool science here to learn. So, once again, for this Friday we'll be giving out eight, you can either do the challenge or explain some topic or you could just post about this class to your friends on social media and they'll, pick someone and all those things work and we kind of track.

It and we'll reward those accordingly, all right, so my friend diana is going to give introduce the question for next week, but first I want to show this clip. I found on social media, which is just so cool. This is a nurse who's going to work and her neighbors came out to surprise her, so got throw the music on and I'll just say. The next two weeks are probably gon na, be like kind of the little weird there's gon na be a lot of people who are you need to go to the hospital social distancing hasn't fully kicked in yet so just be sure that you're super nice to the Medical professionals like that these nurses are literally risking their lives for the rest of us, as well as like the delivery drivers right or the people working in the grocery store.

This is a time just to up our game and to all come together and just be really cool to each other, like what can you do personally, if, even if you're, not in that a professional or delivery driver, just work at the grocery store or something you Know what can you do to punch coronavirus in the face and make someone's day a little bit better? This is like tricky for all of us, so we've got to do our parts, but having said that, you know I have full confidence, we're going to be fine. This is gon na be bumpy, but together we got this. So let me show you this clip from Dianna introducing next week's question: hey Mark, it's Diana from the YouTube channel physics girl. I have a question for you so dire that I had to send you a video message: okay, how do astronauts weigh themselves when they're weightless, when they're floating in space mm-hmm all right, so how the heck do astronauts weigh themselves in space hi? This is gon na.

Be a really cool lesson on inertia and mass there's a lot of really interesting demos and really cool mental models to be updated here. So don't just google the answer just try and think of it. I want creative answers that aren't like the typical. Maybe even that's not even how they actually do it.

That just shows you've been thinking about how they could possibly do something like this. So with that class is officially dismissed. I will go through if I've got some questions and you know you could leave now but I'll answer like two or three minutes of questions and then you know, like I said, answer the questions. The video description do the challenge tag me on anything on social media and we'll give some people some headphones all right, so questions Papa, Papa Papa.

Is that your hand at the beginning? Yes, I do my own stunts good question Shirley. What is your favorite video you've done? I did one on the rover landing. That's like one of my least popular videos, because it was like from 2012 or something, but when the rover we send the Curiosity rover out again next February, I'm gon na rehash that one. I think because it's just it was really cool.

I showed from like a personal standpoint what it felt like to see the rover go to Mars. If you Sam, if you become a teacher, would you be the kind of teacher that would blow stuff up in your class if your class is well behaved and if so, would it be a watermelon, yes and yes, great question Sam? Is that hot, as that pointer a Hot Wheels track? Thank ya that pointers a Hot Wheels track come on only the best here, all right isn't skin, hydrophobic kind of, but not really like it. If you dip it in right, it comes up wet if it's truly hydrophobic, it gets rid of the adhesion, and you wouldn't see that wet part on your skin. It's sort of more or less impervious to water, like if you put it in your your fingers, nails your fingers do get kind of wrinkly on the fingertips and stuff, so not really hydrophobic wate water is magnetic heck.

Yeah water is magnetic. How cool is that? I think you can actually even do this if you put a magnet under water and have it running in your sink. You put a magnet up next to it. You'll get the water stream to actually bend towards the magnet because it actually is magnetic all right.

So is there film on the bottle or that's pretty good, we'll leave it at that? So that's it! For this week, we'll see you or for today we'll see you on Friday because again no class Wednesday thanks so much you guys are the best. This is crazy. We'll see you next time.