Welcome to science class, I'm mark Rover. This is where we answer important questions like what, if all the toilets in the world flushed at once, we have three clues. We try and use as few equations as possible to answer it. This is alive, so anything could go wrong and that just may happen to do it.

Cuz there's a lot of moving parts, and I wish we could rehearse this more. So a couple really fun announcements. We have Kahoot this time so check the link in the video description. If you want to join the Kahoot, I'm gon na ask three questions throughout this and you could try and make a guess and see if you can get it right.

As usual, I'll have a Q & A at the end real quick announcement. As you know, coronavirus I'm making these videos I'm also still trying to fill in normal YouTube videos. I may not be able to do this class next Wednesday. I said we doing weekly, but at this point just consider these babies a bonus, and I will leave a link in the announcement in the the top to pin comment on this video.

Also in the video description, letting you know whether or not we'll have class this Wednesday or next Wednesday. What you should know, though, is this has been a lovely experience for me and even if these live classes, don't continue forever. Some reincarnation of this will be in the future. I've really enjoyed getting more into the physics and the details of this fun stuff.

So don't worry if you've loved this and these don't go forever, as I switch back to my monthly videos. So with that, let's just get right the heck into it clue number one pressure vs. force. What do those things mean? So I've got a book here, a really good physics book and I've got a scale here.

If I put this book on this scale, no matter which way I orient it, what will the scale read? They'll be the same force right if you're standing on a scale in your bathroom, whether you have two feet on or one feet on, it still reads the same now. What about the pressure, though you're like well, I'm not really sure what the pressure is right. If I put it on this edge or this corner vs. flat like this, you can think pressure is like which pokes you more which feels sharper.

And so, if you had your hand here, and you did the corner of the book versus the flat part, which part pokes you more right - probably the corners right. Let's do another example. If I'm walking in my house and I hit a table, if I hit the edge here versus if I bump into the corner, which hurts more, which pokes you mark now remember same force right, it's just me walking into it, but one of them will hurt more And poke you more right, so we're kind of honing in on this concept of pressure. Let's say your friend comes up to you and says: hey Mark.

I want to push on you with one pound and I'm like one pound. That's not that big of a deal, but then I turn around and your friend pulls out. This is just a little screwdriver, which is a little point on the top. It's basically a pinpoint and she's and then and then she's like okay, here's my one pound right.

Instead of using your hand, she uses this, this sharp pin, that's gon na hurt. Okay, remember it's same force. The pressure is different, so we're kind of honing in on this concept of pressure. So there's actually a formula for this.

We use limited formulas, but pressure equals force over area force over area. Okay area means, like you know, if there's a pizza, a bigger Pizza has more area, it's like the inches squared right, so this makes sense force per area pounds per square inch. Maybe you've heard of a pressure in psi pounds per square inch right. So here's the question: let's say you just got new floors in your house and there's two organisms out front: there's a woman with these high heels on and she weighs 10 110 pounds.

Or maybe it's joe exotic, these are nice and tiger right there out front of your house and there's an elephant. You got these lovely new floors and you're like I, don't want them to get ruined, which would you let into your house the elephant or the person wearing these heels, that weighs 110 pounds. So if you said the elephant, you were wrong by a factor of 10, because there's such a small area on these actually do the math. An elephant's foot is like this big around right.

The elephant weighs 5 tons. The woman only weighs 110 pounds, but the pressure from these heels is ten times more than the elephant, which means your floors would get damaged ten times more likely with these heels than a stinking elephant, all right. So now maybe that'll help you understand if you ever on ice and thin ice and you're like holy crud, this might crack. What's your best move, your best move is not to stand straight up and have a small area, because a smaller in the denominator means the pressure is gon na, be more.

You want to like lay out flat or at least go on all fours, because then you're dividing the pressure up between the area. That's touching the ice, so here's a little demo that'll help us understand this. I've got a board here. Okay, here we go.

I've got a balloon all right. If I put this balloon on these two nails, you can see. There's two nails right here: okay, I'm gon na set this balloon on here, put this board down and I'll just set some tape on top whoa big whoop right you're like wow mark; that's fascinating the balloon popped because of two nails. What do you think is gon na happen? If I take this balloon, though, and now I've got 12 nails.

Okay, that's twelve nails that could be like twelve times as many holes. It's gon na be way more pokey right, I'm gon na do the same thing. Put that little lid down, I'm gon na put the tape on now. I'm gon na put the ball on.

It's still not popping. Now, I'm gon na put this box on now. I'm gon na put this Apple on crazy right and now, lest you're. Like Oh mark, will you just using a a really thick balloon: no tricks here, baby, we're gon na spin back around and you'll see when it's on two nails it pops again.

So by the way I just want to teas at the end of this last week. I did the bed of nails, but I just had it on my chest: we're leveling up today. Baby I've got a board of nails right down here. Now I'm gon na lay on 6-inch nails.

Then I'm gon na have the one on my chest and then the cinder block and we're gon na see if I could survive just for me to prove that I believe in physics and I believe in pressure now. Why would the bed of nails work? Why does this make it hurt less? Well, you ever lifted something heavy and the more people you get around the table or the couch it's less force. Each person has to do less right. So there's 12 nails here.

If I put 12 pounds worth of stuff on top, each nail now only has to support a pound of piece. They divide it up, just like lifting a couch right, and so, if there's less force per nail, each nail has less pressure. So that's the physics I will demonstrate my belief in when we do the bent nails at the end. Hopefully there's enough nails that the pressure individually in any spot on my back will be low enough.

All right here we go baby. This is a super cool. One of those mental model things that I love. Okay, I've got this Apple here, I'm gon na try and cut it with the ruler now you're, probably thinking at home mark you are just freaking crazy, there's, no way that's gon na work and the truth is that is not working.

Okay turns out. You can't cut an apple with a ruler. I have a knife: okay, same force, it's my arm same motion, Wow! Can't you see, that's cuts. What is going on there.

That's something obvious that you see all the time, but what's the difference, the pressure is higher. Why it's the area when we say something is sharp? What we're really meaning? Is this there's just less area right here write the number on the bottom is smaller. So when I'm sharpening a knife, what you're really doing is just trying to reduce the area for which you will apply to the thing you're trying to cut remember same force, smaller the area you push just like the pin on your back, the more pressure there's going To be - and that brings us to our clue - number two and I've kind of been alluding to this yeah, but it's pressure or what we'll talk about stress in a minute that breaks stuff. It's not force.

Okay, if you were to zoom in on this Apple, real close, you have these Apple molecules that are all holding hands like the game, Red Rover right and with this ruler. What you're doing because there's like a wide force, you're sending all those people trying to rush into the Red Rover arms over the? Maybe it's like if you zoom in again, maybe it's 12 people and they're like oh, we can handle that right. Each arm they're holding hands. We got this, but when you switch to a knife, it's like hey guys, huddle up now when we charge these guys, let's all go for one person mark and this guy next home.

Everyone go for that that arm instead of spreading out and when you do that my individual hand strength next to the person it's too much locally. It's like a laser beam, it's too much and we have to let go, and so that's what happens. These Apple molecules break because the energy, at that one hand hold exceeds their ability to hold hands. There's something called finite element analysis.

I use this a lot at NASA. I use this a lot when I worked for Apple. So what happens? Is you break them? A fan in this case up you look at each individual, individual and element, and you look at the stress, because stress is basically a pressure as felt by an object or a material, and it's like wherever it's red, it's like yo Red Rover hands. That's too high.

I'm gon na break that's gon na rip off same for like a bridge right. You do this analysis and it's like look. This red spot is too high Red Rover. Hands we're gon na break there and it could be catastrophic, so you either have to change the design or just beef up with some material right in that spot.

So, okay, here we go we're gon na change gears just a little bit a new breakfast, so I'm gon na have a little bit of Apple. Now, let's talk about liquid pressure. Okay, we talked about this in the pool eating that Apple. As a mistake, we talked about this in a pool when you Poole your ears, hurt right because there's so much stuff above you, it's like being in the bottom of a dog pile.

There's lots of water molecules the deeper you go. The more your ears hurt the more pressure you feel right. So here's our first Kahoot question: I've got this 3 litre bottle. There's three or two liter bottle.

There's three holes in it. I want to know which hole is gon na shoot the water, the furthest, this bottom hole, the middle one or the top I'm gon na shoot it off the edge and of his bucket below okay. Let me get it set up here. This is live, whoa, easy girl, okay, take off the top.

So did we put the question in okay, so it'll be ten seconds? Okay! So now we're asking the question: okay, so go ahead and let's see not this one, okay, I put it out of order. I missed my buddy Josh here out. Actually, this is a better one to start with. Okay, you want to keep that one up.

We're live, we're live okay back to me. Can we go back to that Josh or do we already lose it? Okay, I'm s! Josh! Yep, basically, we had some vases that had different shapes. The point was the okay yeah right there. The question was on which of these is the pressure.

The greatest a B, C D and E now remember my excel stories. Remember that all that matters is the depth right, so the correct answer is even though these have different shapes, it's all the same pressure at that same death. Okay. So now, let's come back to here.

Let's do the next question, which is what I'd previously setup: we're live baby so which hole is going to shoot the bottom, the furthest, the top one, the middle one or the bottom. Okay, we're getting the answers in okay at home, even if you're not on the Kahoot. If you're watching this delayed go ahead and answer what you think the answer would be well, I get this right. Okay, do we get answers? Alright, so most people said is that in the top, the middle most people said the bottom, which was the red one right.

Okay, most people set the middle all right here we go. Let's see four right here, we go now remember where's the pressure the highest, the deeper you go and if you have a squirt gun, do you want it to have high pressure or low pressure? Well, high pressure means you're, shooting farther right. So, technically, I would think it's going to be the bottom one, because that should be the highest pressure right. It's the squirt gun with the most pressure here we go.

Let's see and look at that. I don't know if you could see there I'll, try and line it up, but the answer is in fact the bottom one is shooting the farthest. Hopefully you can see that on one of the cameras. Okay, here we go and you really are seeing it.

Now. You see that bottom one, the top one, doesn't even have any air, because that is where you have the highest pressure: get in there. Okay, all right! So, let's see, let's do another example of this where let's bring this bucket up Alex. So the way to think about this, the reason if you go back to the vases, where it's like all that matters doesn't matter the shape of the pool you're in right.

All that matters is what's directly above your head, so think of you're in a pool the pressure you feel it's kind of like stacks of plates on your head and whether or not there's a lot of people next to you with stacks of plates on their head. The only thing that matters is what's directly above you so another way to phrase that is, I've got this big tub here. That's really deep. This is a big swimming pool and another one here they are the same height.

We have a coupe for this one. Oh yeah, so they are the same height in water, which will shoot further, which pressure will be greater okay, well, based on what I would just said, miss that a little bit. They should shoot the same right and sure enough. We can see in case it doesn't tilt back camera now in just slightly Josh and back up.

They are shooting the same. This one drained faster, so it went a little bit more but right at the beginning, now that this load level is lower, it's not shooting as far they're shooting the same distance. All right Alex. Let's come take this away.

Here we go okay. So what the heck does all this mean? Well, there's a very common case where you see people taking advantage of this concept of fluid pressure and using it very cleverly around like just basically in and around anywhere you go. Here's an example of one right here. What you'll notice here see these little Pistons, those are filled with oil.

Those are filled with fluid and maybe you've noticed before these little hoses. That's pumping oil in and out of this piston. Let me show you how that works here. So let's come back here.

Let's go to the tight camera; basically, I've got these hydraulic. These are those little syringes here right. Well, as I push these in and out, this thing moves up and down right. You can see.

I have three degrees of freedom and I have three ways to toggle it. These are just little syringes filled with water liquid, and so this is taking an advantage of the fact that water is incompressible and I could have a pump way down here at the base of the excavator and up here I could use some mechanical advantage and I Could get it to do a lot of work? You see hydraulics like this in a lot of cases, so this actually demonstrates Pascal's principle, and I should say by the way this is from Kiwi Co. I asked them to borrow this and they said hey Mark. While we just sponsored this livestream, so I said: okay cool, I'm a huge fan of what they do and you should know by the way, if someone's getting money to say something being sponsored, you should always take with a grain of salt.

You should also know that I say no to like 95 % of the people who want a sponsor with me on my channel unless I truly believe in their product and that's the case here. They have monthly crates from ages 2 up to 16 years old. I went there the other day. You can see this.

This is me with my buddy Destin, so we're playing air hockey with a little inverted balloon, which I'll explain here hockey table would be super expensive. So you could turn it on its head. Instead of having the tea will have all the air you do it in the puck check that how cool is that - and people have told me like mark you - should do a crate. Well, it's like I.

I don't know what to do to improve on what they do. I seriously love what they do and what they stand for and how they do it, and so I know their president Sandra she's super cool, it's just a great company and I totally stand behind way. They do it especially right now, obviously everyone's stuck at home. They come to your house, they have these kits, you get to put them together.

You get to learn science. They have little booklets that teach you cool things about what you're putting together so Cuba. Cocoa, slash mark rover, there's a link in the video description and you get your first month free and I honestly think if you love my science classes and what we do here, you will absolutely love what they do, what they stand for your kids. I look forward to getting these every month.

We get a couple boxes to our house. Okay, so with that in mind, it's time for our last clue, water towers you've seen what of waters you may have seen this before. This is a water tower. What's the purpose of a water tower, have you ever wondered that you see these especially like in older cities? The goal for a water tower coming back to me, is basically to put those water at a high height high potential energy right.

We talked about the pool the lower. You go only thing that matters is height, doesn't matter, however, you get there, the lower you go, the bigger difference who the water between where the water is stored and where the water comes out is how much pressure you'll have. Okay, so and a lot of times the water treatment plants are at a lower likely to kind of by the ocean. So it's like that Delta.

That makes the big difference that gives you water pressure, basically in your house, so the question now what happens then, if all the toilets flush at once so we've got one more Kahoot here and we'll put it up. So tell me what you think the answer will be: what happens if all the toilets flush at once? Is it not much like a little bad or nothing bad? Let's see, based on what we've talked about so far. Okay, it's basically split right down the middle, and the answer actually is a lot bad happens, because if you think about what's happening, these toilets in the of themselves hold water they're like little water towers themselves when you flush the toilet. All this water comes, that's gon na be a higher potential energy than the water treatment plant, and it starts with like four inch pipes from your house and it gets to the street.

Maybe it's like what like a foot? Eventually, you get like ten foot pipes as you get closer to the treatment facility, but even that we'd get oh it's so overloaded with water. The pressure would be too high, especially it points in the pipe that are like, lower and they're a little bit weaker. Maybe a little rusted, it would absolutely burst through the weak spots in the pipe. On top of that, you know you have sort of these like lift stations that sometimes, if you have to get over a mountain, the water stacks up there, you lift it up, get over the mountain and then keep going down.

Those would absolutely get backed up, and so the water that was on its way up the hill would then come back down, and then this is the real kicker all that raw sewage would come back up the pipe into the pipes up through your toilet up through Your sink up through your washer, it's bad news. I have this clip here of this dude in France, who recently tried this with Orbeez in his bathtub. You might have seen this. He didn't.

Do it like me, you're supposed to use salt dude when you're done to make it shrink down, and so then, because all the pipes in your house are connected, naturally witness toilet written to his sink, and then he tries to flush the toilet with predictable results. I can't speak French or German, but I don't think what he's saying you should repeat, and and not only that isn't in his house, but he went outside it's coming up through the storm drains right and then the police come and it doesn't end doesn't end very Well, so alright, that's the answer, then bad things happen. We're gon na end with me on a bed of nails, as promised for me to prove that I believe in this physics stuff. So once again, this is what I'm gon na lay on.

Okay, here's an apple show, I'm not making this stuff up. Why does that happen? Well, there's a lot of pressure and, like we said pressure, is what breaks stuff, so it's breaking the skin on that Apple. This is the board I'm gon na lay on this is the board. That's gon na go on top of me by the way.

This really is dangerous. I'm gon na lay on this and it doesn't feel great. So this is one example of what you should not try at home. Even on your adult supervision.

I would not recommend this all right. I don't want to get sued okay here we go doing this for physics, yah. Okay, if I was laying on one nail, that'd, be terrible right, but luckily all the nails are spreading this out. Oh my hat.

Okay, now we're gon na put this on my chest. Here we go. Oh boy, it's like a marker. Over sandwich of nails now comes on block.

Oh I'm, making poor life choices. Okay, I'm doing this one for physics Alex! Don't not yet he's gon na crack this with that hammer and remember the things that helped me out fact that this brick here actually kind of helps me. It's inertia right, helps me from stealing some of the blow the fact that this brick will hopefully break that. Will take some of the energy with that? I'm ready to prove my belief in physics, Alex you ready.

Three, two one, okay go back to the wide camera Alex. Oh, I just approve. Let's do a test here! You take a drink of water; no waters leaking out. No holes baby, we did it pressure, that's what it's all about that worked because there was a bunch of nails to help sort of diffuse that force right.

Okay, so I'm gon na give you guys the challenge for this week. Okay, before we do that, I'm just gon na tell you about a link in the description, and now I'm gon na play the music. My buddy jacksepticeye did a stream. Yesterday they raised 1.7 million dollars for this whole Cove in 19 thing.

If you've wanted to help donate money but weren't sure where to do it tilt, if I set up this this, this funding thing, the money goes to the United Way, the United Nations Foundation and Red Nose Day, splits up between those three things. So I made a donation if you've wanted to help but weren't sure where this is like a super vetted way to put your money to really great use, so that link is in the video description shout out the jack for being awesome. Okay, here's the time whenever we meet next here's the question for my friend Dustin: let's see I'm going to skip that video first hey Mark its Destin, so we are out here on the front line. Well, actually, we're not the frontlines we're trying to get these space shields to the frontlines, so that doctors and nurses can use them as they work against the virus here, but I know you're doing a livestream today and you're answering science questions and so one question I Had is: is it possible to survive a landing without a parachute? Is there a way to do that? Let me know okay, so the question is: if you jump out of a parachute and your parachute fails, how can you survive that there is the way it's a small chance, but there's a way you could survive that all right.

That's what we're gon na talk about! Next fascinating topic: now I'm gon na show you some results from last week's challenge: the people who got a bunch of Bose headphones and then I'm gon na show you the challenge for this week or give you the challenge for this week. So here are the some of the responses we got. There's been so fun to see these responses. So once again, I think I just want to keep it open-ended and just blow my mind.

Come up with something cool teach me about some principle: teach your friends about kind of you know: pressure versus force, Pascal's law, what it means to have something sharp anything along. These lines talking with pressure, different depths and then the winner this time, six people will get a three-month three free months of boxes from Kiwi Co, because they're awesome so blow my mind. We'll pick the people you will get them we're gon na do a QA now. So class is technically officially dismissed, will do the QA and then don't forget.

We may not do it next week. I'll put the link in the pinned comment and the top in the video description to kind of let you know, but otherwise be friggin awesome, so classes dismissed under like three minutes worth of questions. Thank you. There's my phone and and then you get the heck out of here.

Okay, here we go. Did that hurt yes a little bit once again I mean it didn't hurt that bad. Obviously, if I did one nail I like would have a punctured lung - and I would be here at this moment, so it didn't hurt so bad. But let's see do you have any tinkerer crates? Yes, I honestly get these.

We get a couple every month and we forget love doing them, they're great. What is, did you want to be a physics teacher when you're little? No, I mean once I took physics I thought well, this is cool and I just love talking about this stuff. With my friends, so it made it a lot: more fun: okay, okay, how do toilets work in space? I'm not perfectly qualified to answer that, but I, if I recall they kind of have like a vacuum tube. Obviously you couldn't flush the water no gravity.

So it's some form of like a vacuum tube. Why doesn't gravity crush us great question? That's a topic for a future science class. Remember we are in a fluid air, is pushing around us all around just like being in a pool, and you feel that pressure, but we're gon na talk about gravity and stuff in a future class. Okay, so that's it be good.

You guys are awesome thanks for being here. We're live, we'll see you next time blow me away with cool demos, bye.