I'm about to plug in this fan to test
whether blowing on this sail will move the boat forward. And then I'm traveling
4000 miles to the equator where I'm actually standing in both
the northern and southern hemispheres, because this line here is the equator,
and I'm here to investigate whether or not
this demo for tourists is a scam. Basically, they pour water in this basin
and on the north side of the equator, it seems to swirl
and drain counterclockwise, but just a few feet away
in the southern hemisphere. The water seems to drain in the exact
opposite direction. It's sort of like
how you also might have heard toilets flush in opposite directions
on different sides of the equator. And we're here to uncover the truth. But I'm not stopping there because today
we're going to investigate six other physics and engineering puzzles
using simple demonstrations as we go. Because our goal by the end of this
video is for you not just to know the right answers,
but more importantly for you to understand
and why they're the right answers. To kick things off. Speaking of Hemispheres did you know the moon in the sky looks like this in the Northern
hemisphere, like in Canada. But it looks like this in the southern
hemisphere, like in Australia. It's upside down! And while that is a fun fact,
it's even more fun to understand why. And this is why As we all know, the Earth is... a sphere. So if you were Superman
standing at the North Pole in the Northern hemisphere,
you'd look like this. But if you were Thor standing in the southern hemisphere
in Antarctica, you'd look like this. Now, of course, the moon over here
orbits around the earth like this, and I'm going to add an arrow
to it to help us with orientation. And so to the Superman at the North Pole That arrow would point up, but from the
perspective of Thor at the South Pole That arrow would point down
from his perspective. And now I know what you're thinking. If all that's true,
then which way would the arrow point? If you're Spiderman,
standing here at the equator. Well, according to our model here,
it should be sideways and sure enough, here in Ecuador,
at the equator. I'm happy to report that the moon does,
in fact, appear to be sideways For fun fact two of seven. If you just stick two pins into some cardboard like this
and then connect them with a string and trace it out, you get my favorite
geometric shape... an ellipse! But there's something really special
about these two pinholes. They're called the focus points. And any straight line you shoot out
in any direction from one of the points will bounce off the wall of the Ellipse
and always hit the other focus point. And here's proof
because I've got a laser pointer at one focused point,
a ball of wax at the other, and a mirrored surface
all along the interior wall. And now you can see, no matter which way
I point the laser, it always bounces off
and lights up the wax. But here's the really cool part. If you build an actual full sized room in the shape of an ellipse
and then you stand at one focus point, you can hear even the faintest
whisper from anyone standing at the other focus point,
even hundreds of feet away, because all the sound waves bounce
right back to your ears in fact, this actual ellipse shaped room
was built by John Quincy Adams in the US Capitol building. And legend has it, he was a master
at anticipating the moves of his opponents, plotting against him
on the opposite side of the large hall. And now that you know
the physics involved, it should come as no surprise that
John Quincy Adams conveniently placed his desk right on top
of this leftmost focus point. Next up at number three, everyone knows when you slam on the accelerator pedal in a car,
the stuff in slides backwards. And then when you slam on the brakes,
the stuff inside just keeps moving forward, including you, by the way which is why we were seatbelts. So then why the heck
when I'm driving to the birthday party and I have to slam on the brakes does the cake slide forward? But the balloons
actually move backwards? Now as for the cake sliding forward Well, that's just Newton's
first law in action, which basically says all stuff
is kind of lazy and wants to stay still unless a force comes in
and tries to move things. And then Newton's second
law tells us that the more you weigh and the more mass you have, the more force
is required to even get you to move. But here's the thing
we sometimes forget. The air around us is a fluid
and it also has mass. It weighs something. This is why air pressure is a thing. There's tons of air molecules stacked up above us
and they each weigh just a tiny bit. So we are like at the bottom of this air
molecule dogpile. This is why your chip bag expands
when you head up to the mountains. It's because it's moved up the dogpile. Now there's less air above it, weighing
down, pushing in on all sides. And for a little proof,
here's a simple demonstration that the air molecules around us
do actually weigh something. When I throw this balloon at the sign,
it moves, but it doesn't quite knock it over. Now, all I'm going to do is take that
exact same balloon and just add air. That's it. Everything else is identical
and unchanged. And yet now, it bonks the sign over. So that means we increased the mass
only by adding some extra air. Because again, Newton's second law states the heavier, the more massive a thing is the better it is at bonking things over. So in the car,
when you slam on the brakes it’s not just the stuff in the back
that has mass that wants to keep moving, but all that invisible air does too. So the air itself also sloshes forward
when I slam on the brakes. And since that air is more dense
than the helium gas in the balloon, the lightweight
balloon gets forced backwards. And that's what we'd expect, right? We say a helium balloon floats in air or this ping pong ball
floats in water but it's almost more like
the heavier, more dense thing in this case, the water rudely cuts to the
front of the line forcing the poor
ping pong ball up and out of the way. In fact, you can see
if we lay this jar on its side. The same thing happens as in the car. When I give the jar a push, the water sloshes back,
which forces the ping pong ball forward and then when it stops the water sloshes forward,
forcing the ping pong ball back then for number four,
we're back here on the lake to figure out if sailboats move
by having wind blow in their sails Why don't they just get
a big old fan like this to power them through the water? Sort of like the guy in this viral video
who's using a leaf blower pointing into an umbrella
to scoot his way around on a skateboard. Well, let's think this through
with the simple demo of a fan that's attached to this train car. When I turn the fan on and it blows air to the right,
which way will the car go? Well, of course it goes to the left
because it's basically cutting through the air
and pushing it backwards, which creates an equal and opposite
reaction that pushes the train forward. Just like an airplane propeller pushing
air backwards, moves the plane forward. It's so different than me
standing on this skateboard And when I push watermelons to the left,
they push back on me So I roll to the right NATE! AGAIN!? And so now let's place a brick here
so this car can't move. And then add a second car here
with a sail. Now, when I turn the fan on, which way
will this cart move? Of course, to the right. Because all that fast moving air hits
the sail. It's like it's being bonked
by all those tiny little watermelons. So if we now remove the brick
and this cart wants to move to the left, and then this one
wants to move to the right, what'll happen when we connect them? Nothing, because it's a perfectly timed
tug of war with each car trying to move in opposite directions
with the same amount of force. A fan actually sort of does
work to move a boat forward, you just have to lose the sail
and point it the other way. But at that point you might as well just take that same fan
and stick it underneath the boat so you could much more effectively push against the heavy water
instead of just air, which is, of course, exactly what a boat
propeller does. And sure enough, when I plug it
in, in real life as you can see, I don't go anywhere. So then if we've totally debunked
the idea of blowing your own sail, then what about that guy with the leaf
blower and umbrella on the skateboard? Well, I've copied his exact same setup
here, and I can confirm it actually does work. Yeee Hooo! Yeee Haaa! It just
has nothing to do with the umbrella or the leaf blower and everything to do with the fact
that this is an electric skateboard with the battery stored
right under here. Exactly the same as you can see in
a bunch of these shots from his video. Now, before we get to the last three,
including answering if this demo for tourists is a scam,
if you're like me and you love that ah-ha moment
when you learn something new well, I got great news for you. Let me guess. CrunchLabs? I'm glad you said it, Jimmy.
That's right. Because packaging up that movement
is why I created CrunchLabs, where you get a super fun toy
every month in the mail that comes with a video where I teach you all the juicy physics
that make the toy work. Mark won't say this himself, but obviously he used to work at NASA
and Apple. He's one of the greatest engineers
that you can ever find, and he's specifically designing
these boxes teach you all the stuff he learned He had this water gun that we made. And you can flip a switch
when you give it to someone else and it shoots back at you. I mean, that's awesome. I've pranked you a couple times
with the boxes, Jimmy. I know. So if you want to prank MrBeast while experiencing a bunch of those lovely ah-ha moments
at the same time It worked! just visit crunchlabs.com to learn more. Yesss! Now coming in at number
five is the craziest fact I know Imagine I just finished tying
this rope all the way around the world, but now I just found out it was supposed to be a foot off
the ground the whole way around. So the question is how much more extra
rope would I need to buy to add to this rope to make that happen. Now, you might be thinking double
or even triple this amount, but what if I told you
you only need this much extra rope 6.28 feet to be exact. Think about that. The circumference of the earth
is 131 million feet. And yet you only need this much extra
rope to lift the whole thing a foot off the ground
all the way around. And what's even crazier is
if you did this around a basketball, it would be the exact
same amount of extra rope. Now the math is just some
straightforward eighth grade algebra. And you can see here because the radius cancels out,
it doesn't matter what size circle you use, it always works out to two pi
or about 6.28 feet of extra rope. But if math isn't your thing,
don't worry, because if you just pretend
the earth is a square, it will immediately be obvious why
the size of the object doesn't matter. So if this is my initial rope When I raise it off the earth by one foot, you can see in each corner
I only need two extra feet. So eight feet total. And just like with the basketball,
you’d still get the same answer If you try it on a smaller four-sided
shape like your TV, which is pretty close to the 6.28
extra feet needed for a circle. At number six,
there was a Kickstarter a while back. that claimed to have invented
a floating backpack that reduced impact forces by 86%. Welcome to the Future of backpacking. You've never seen a backpack
that moves like this or that lets you move like this. And this motion isn't just for show. By suspending the load, hoverglide
reduces impact forces by 80 to 90%. I really took an interest
once I noticed a lot of people in the comment section were debating whether or not
this would actually help. So what do you think? Is this a scam? The case for it not being a scam
is that when you wear a normal backpack as you bounce up and down with each step you take you're working against gravity
as you move that entire weight up and down with you as well. Sort of like pulling this weight
up and down with a stiff rope. But if the backpack was elastically
suspended on a track, its own inertia would tend to keep it
vertically in the same spot. So you can still bounce up and down
while the pack wouldn't move so it’d be like replacing that stiff rope with an elastic one at which point
you can see it makes it a lot easier on my arms moving up and down
as the weight stays in place. But the naysayers pointed out all the pulleys, cords and extra frames
to make the system work is still an extra
4 pounds of weight. And whether it's bouncing or not,
you're still carrying four extra pounds to the top of the mountain. Plus, the video just shows
the ideal use cases, and in real life it probably wouldn't work that smoothly,
hiking over rough terrain. And I felt like both sides
sort of had valid arguments. So as a firm believer in the scientific
method, I ordered one myself. And then went hiking for a few miles with a normal backpack
and then put the exact same amount of weight in the hover glide backpack
to qualitatively compare the difference. So far, I don't like it. Feels like
it's, like, rocking me back. I’m going to try jogging. oh that feels good. That's kind of the trick I feel like if you hit the right cadence,
it's magical. if it's not the right cadence, It's the opposite of magic.
oh yeah. Now it's. And then it gets out of sync, throws
you literally off balance So my verdict is that on flat,
predictable terrain, it can be beneficial. But on any sort of rough, sporadic
hiking terrain, it's just not worth the extra weight in force
from out of sync issues. And for our final science challenge,
we're back here at the equator in Ecuador to see if this popular
demonstration for tourists is actually a scam. Does the water really drain
in opposite directions, even just a few feet on either
side of the equator? And relatedly, do toilets also swirl
in opposite directions in the northern versus
southern hemisphere. Now, for the toilets, let me just debunk
that myth out of the gate, because if you look
closely, the swirl direction is just a function of which way the nozzles
point, as you could see here. And with any toilet
you inspect yourself. But what about sinks
that have just a drain like in the demo here
where there are no nozzles? Well, believe it or not,
there's actually some truth to this idea because of something
called the Coriolis effect. And it's the same reason
you might have noticed weather patterns like this spinning counterclockwise
in the northern hemisphere, in which case we call them
hurricanes and clockwise in the southern hemisphere,
in which case we call them cyclones. And the reason for this
is pretty straightforward to understand If you imagine you have a very big sink
that spans from the equator all the way up to the North Pole,
In that case, a single drop of water in the sink at the equator here is going for a joyride
really fast as the earth spins and a drop of water near
the middle is moving at a medium speed. But a drop of water at the North Pole isn't moving at all
because it's right on the axis. So now when you pull the plug
on the sink and the water moves towards the middle,
the joyriding drop here is suddenly moving faster than the slower water
that was away from the equator. So it gets out in front of the drain and conversely, the drop at the North Pole is now moving much slower
than the water closer to the equator. So it falls behind. So when all the drops
are affected this way you naturally get a counterclockwise
swirl just like a hurricane where the eye of the hurricane
is the low pressure zone like a drain. Then of course, applying all this same
logic to the southern hemisphere would of course do the opposite,
resulting in a clockwise swirl. So does this mean that sinks
do in fact drain opposite in the northern
and southern hemispheres? Well, sadly, no, because the Coriolis
effect is really only noticeable The greater distance you're moving up
or down from the equator. So unless you have a five mile wide
sink, or if you make the most perfect of perfect conditions, like my friends
Destin and Derrick showed, The water is flowing clockwise
due to the earth’s rotation The water is going counter clockwise
because I’m in the northern hemisphere It’s real! this effect is way
too small to have any meaningful impact on the swirl
directions of sinks and toilets, at which point it comes down to other factors
like sink geometry or the fact that the seemingly
still water was actually still barely moving around
when the plug was pulled. So then what about that tourist
demo? Well, if you play it back and look closely,
you can see the end of his pour. He does this subtle twisting motion
so the water would just continue to swirl in the direction of the twist. So when he finishes the pour here, he twists this way and the water
continues swirling that way. And then after moving the sink,
allegedly over the equator, he finishes his pour,
twisting the opposite direction, and then the water swirls
in that opposite direction. In fact, you can easily recreate this
demo yourself at home to see that by copying this method, you can also easily get a whirlpool
in both directions and therefore it should come as no surprise that
when I ask this question does it work even like if I pour the water, I was denied the opportunity to test and observe on top of all that
as the final nail in the coffin If you actually look up
the GPS coordinates of this place, it’s more than a football field
away from the official equator, which means we were actually in
the southern hemisphere the whole time. So instead of actual science,
this is just an attempt to take your money
with nothing more than a lame magic trick where the real magic
is all that new juicy knowledge I just wirelessly transfered
through that screen you’re watching me on from my brain
into yours. It's a new year,
which means it's a great time to invest in that passion for learning,
because that passion is not only the main driver for why
I make these YouTube videos, but it's also why I created CrunchLabs where we ship a really fun
toy to your porch every month. And not only do you learn how to build
and think like an engineer, but you learn the fascinating physics
and engineering principles that make the toys work. Every month is a new principle,
and the best part is just like how you hopefully enjoyed
watching this video. It doesn't feel like learning
because we're real good at hiding the vegetables. And what I mean by that is 87% of kids
rate it an eight through ten on a fun scale out of ten. But also more than three
out of four parents said their child gained a new passion around STEM and
engineering after getting the build box. Yessss On top of that, each month,
your box has a chance to contain the platinum ticket
and if you get it, Well then you coming out to CrunchLabs
to build with me and my team for a day. So if you want to invest
in the superpower of having a passion for learning,
just go to CrunchLabs.com or use the link in the video description
to get your build box subscription today. Thanks for watching.
