How I Proved the Earth is Round (with my Bike and Two Sticks)

Around one in every 10 Americans say
that they believe that the earth is flat or that they at least have their doubts
that it’s round. I’m going to test that. I’m going to test if the earth is flat
or not, and to do that I actually need to go somewhere where it’s super flat. So, that’s why I’m going to Regina, Saskatchewan, in Canada, and I’m going to
measure and calculate the size of the earth using just my bicycle and two
sticks. This is not a joke. I’m here with Casey at the Saskatchewan Science Centre
and we’ve got two identical Sundials set up right now since they’re in the
same place the shadows are the same length. But I’m gonna be leaving one of
them here with you Casey – you ready? okay! He is going to set it up on this
very spot right here, and I’m taking the other sundial, and I’ve strapped it to my
bike and I’m going to bike down that road right there. That road is the
reason that I’ve come all of the way to Saskatchewan, because that road is
perfectly straight for somewhere around 140 kilometers and I’ve come to measure
that distance on my bike. Okay so I just zeroed the odometer. Let’s get started.
Here goes science! Okay. This is highway 33 and since it’s very flat here and
there are no mountains to go around or hills to go over, this is one of the
longest straight roads in the whole world and that’s why I’m her. Let’s
pretend that this orange is the Earth. now this is
earth and these two sticks are gonna be the two sundials we’re working with. So I’m gonna put
them in. Don’t try this at home please! Okay, since the orange is round any time we line up the shadows like this they will
never be the same length. If the shadow on the right is short we can expect the
one on the left to be longer. If they were the same length than the orange
would have to be flat. Now we can also measure the length of the two shadows at
the same time and measure the distance between them and figure out the
circumference. Since the Sun is really far away we can treat its light as
coming in parallel lines and therefore we can figure out what angle it’s
hitting both of the sticks at. And that allows us to figure out what angle the
two sticks would meet up at in the center of the orange without having to
pull the orange apart. Let’s say that this angle here is 45 degrees.
That’s 1/8 of a circle, so the distance between the two sticks – this distance
here – that is 1/8 of the circumference around
the orange. So we measure that distance we multiply it by 8 and we know how big
the orange – or the earth – is. That’s what I’m doing except instead of these two
sticks we’re using sundials and instead of measuring this with a ruler I’m
measuring it with my bike right now in Saskatchewan. I’ve got the wind in my back
and it is a beautiful day. I’m clocking at 28.8 kilometers an hour. This is just
great! Things are awesome! To celebrate the 100 kilometer mark I’m going to eat
the earth. It’s pretty good. It shouldn’t surprise
you that I’m not the first person to do this experiment. a Greek scientist named
Eratosthenes did it 2200 years ago except instead of it being in Regina and
Stanton he used the city’s Alexandria and Syene,
and those cities were 800 kilometers apart. He didn’t have bicycles back then
so he had someone pace the distance between the two cities
which is crazy – I mean they were 800 kilometers apart! And his measurements and
his calculations were so precise that it was still within 1% to 16% of the
actual circumference of the earth. That’s incredible. But we don’t know exactly
what his answer was because he used a unit called ‘stadia’
which was how big a stadium was, and there were different sizes of stadiums
and we don’t know what one he meant, so his answer has been lost to the sands of
time. But, I’m gonna try to redo it with a huge upgrade in technology we’re using a
bike. I biked a hundred and thirty-eight kilometers today from Regina to reach
the first stop sign it’s the end of the road and it is Stoughton. Ok so I just
set up one sundial in Stoughton and Casey set up the other one in Regina we
made sure that they were both level and checked that they were both aligned with
one another and everything seems to be good okay. I think my math was a tiny
tiny bit off because I thought that the measurement was going to take place at
10:59 and it is 11:04 and we’re still a few minutes away so I think it will be
more like 11:15 but you know with this experiment what matters is that the Sun
dials are lined up with the road and lined up with each other and I just got
off the phone with Casey and Regina and we are at the exact same point, the exact
same angle right now, with our sundials. At least this angle is the same. (yeah I
know a little nerve-racking right?) We’re really close though! Mine is officially
on the meter stick. Is yours almost there? Okay
so in, well in another like maybe.. we’ll say ten seconds you can grab your chalk.
your line looks pretty good right?! So this is it okay okay we’ll take the
measurements in three two one now I’ve got okay I just measured my shadow and
mine was 66.1cm, and then I called Casey
and his with 70.0cm which means that our shadows
are 3.9cm different! Mine is 3.9cm smaller than his is in Regina, which means that the earth is a
sphere! And it means that I can calculate the size of the Earth. Now I expect that
it won’t be exactly accurate but it’s going to be pretty darn close. Oh that’s
really really rad! Okay, cool… I’m gonna hang up, and get packed, and get on the
road. We now have all of the measurements that we need in order to do the
calculations for the circumference of the earth. So I left Regina on my bike
and I cycled all the way to Stoughton. that distance was 138km when I got to Stoughton. I set up a sundial that was 100
centimeters high and I measured the shadow of the sundial at a specific time.
The shadow was 66.1cm long and so we can do some
simple math to figure out the angle at which the Sun was hitting the top of the
sundial and that turns out to be 56.5°. Now at the exact same time I was taking that measurement, Casey in Regina was taking another measurement
on an identical sundial. his measurement was 3.9cm longer – he measured a shadow of 70.0 cm and that
means that the earth is a sphere and we can calculate its circumference. We use
the same math to figure out the angle that the Sun hit the top of his sundial.
That was 55.0°. Since we know the angle that the Sun hit
both of those sundials, and since the Sun is really far away, we can calculate
the angle that those two sundials would meet up at if they met in the centre of
the earth. We take the angle from Regina and subtract it from the angle in
Stoughton and we get 1.5°. That means that the angle that
those meet up at in the center of the Earth is 1.5°, or 1/240th, of the circumference of the earth. And now.. Now that we know that the
distance we measured is1/240th of the way around the whole
earth, if we take the distance that I measured (the distance that I biked) and
multiply it by 240 we can figure out how big the circumference of the entire
world is. When we do that we end up with 33,120km. By my calculations that is the size of the earth, and it’s
pretty darn close. The true size of the earth is 40,075km which means that my measurements and calculations are only
17% off. Eratosthenes’ measurements and calculations were, maybe,
16% off. I’m really happy with how that turned out.
When Eratosthenes did this experiment over two thousand years ago he not only
proved that the world is round but he measured it and proved that it is a
knowable thing. The earth is something we can experiment
on and learn about. I’m really happy with how well my
experiment turned out because I have confirmed that the earth is indeed round
and I measured it to be 33,120 kilometers around. And that’s not exactly
right, but I mean my measurement is closer to
the earth than it is to Mars and I’m pretty happy with that. The reason my
measurement isn’t a hundred percent accurate is because I didn’t manage to
line things up perfectly, so we took the measurement about 12 minutes too late,
which is enough to make an error of 17% But still, I’m really, really
happy with how well it turned out. I try to do experiments that are almost
impossible – that are just at the border of being impossible [for me], and so if they
always worked out perfectly 100 percent of the time I think I wouldn’t be trying
things that are hard enough. Sometimes I get asked ‘how do I make enough money
from these videos to fund big science projects like this’ and my answer to that
is that I don’t. I don’t even make enough money from this channel to pay for my
expenses let alone my time, but if you want – so that means someone just
subscribed to my channel – if you want to support what I do here on this channel
please check out my patreon page every little bit helps and actually every
patron adds a drop in the bucket. Another way you can support me is to subscribe
to my channel and like this video. It’s not just meaningless Internet points it
actually effects the algorithm which changes how many people will see my
science content. So, that’s huge for me. lastly I absolutely need to thank Casey
and Ryan and everyone at the Saskatchewan Science Centre for making
this whole project possible. It just wouldn’t have been possible to measure
the earth without them, so, please if you’re in Regina: check out this place! It
is amazing. And, check out their website I’ll leave a link in the description
below. Thank you so much for watching!


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