I was watching YouTube, and I came across
some people who say that passenger jet
airplanes are not really travelling as
fast as we're told, and I wondered:
Is there a way to look at the video
evidence and find out?
Oh, and what does this have to do
with the shape of the earth?
[Music]
Guess what!? There are people who
really do think that the earth is
literally flat - as in not the shape of
a globe, but flat.
And...  they think that the government
is lying to us about all these things.
Now this is a whole rabbit
hole if you start looking into this,
with a whole bunch of weird, related ideas.
>> Earth is a level motionless plane.
>> If anyone was to Google world time zones
>>The Sun, Moon, and stars
revolving over and around us
>>they would find only flat maps
>>just as you experience every day
>>The debate is over
there is nothing...
>>Just like a rainbow: it looks like it's curving
when it's actually not
>>... to debate. The earth is flat.
>>The sun does not rise and set.
>> you can't... you can't show me the curve.
>>Now I have a question: Why do people think
the earth is flat?
I have a surprising answer:
and that's because
it *is* flat... ish
It's pretty much flat everywhere you look.
The horizon is flat.
You can't see a curve. So I suppose at
first glance it seems flat.
But how would you know if it's actually flat
everywhere, or if it's just a slight
curve on a really big globe?
That brings up the philosophical idea of epistemology.
One day, I might make a whole video
about conspiracy theories,
evidence, truth, rationality, belief.
But for now I'll leave that all aside and
take a look at a small related question:
How fast do passenger jets fly?
So it turns out the sizes and speeds are
all sort of related to the shape of the
Earth and flight paths and distances
between cities.
So how fast do jets fly?
Well, the standard answer is more than
500 miles per hour at cruise altitude
and about 150 miles per hour when
taking off and landing.
But there are some people
who think that this is all a big lie and
the planes don't really fly that fast.
>>Now I'll back it out, you gotta just see this
as ground speed.
His ground  speed can't be more than
50, 60 miles an hour. Look at that.
>>Really slow, guys. That plane is going really slow.
>>To my eyes, guys, I swear that looks
like 60, 70 miles an hour.
>>Okay, so who's right?
I'm going to  show you how to use a little bit of simple math to find out.
First of all, here's a quick description
of how to measure speed.
Speed is just a ratio, a fraction:
distance divided by time.
So if a train goes 50 miles in one hour,
we say it's going 50 miles per hour.
That's the same speed
as going 50 miles per 60 minutes, 
or going 5 miles in 6 minutes.
These are all just different fractions
with the same value.
As another example: if a car
goes 500 feet in 2 seconds that's
250 feet per second.
Or you can convert that to miles
and hours to get 170 miles per hour.
So that's all you need: distance divided by time and that gives you speed.
Let's take a look at some examples with jets.
There are two basic techniques: 
first let's take a look at some videos
taken from inside the plane, where the
camera is moving against a background
and we're calculating the speed of the camera
In this video from a plane landing in
 San Diego, we can see that
it's near the intersection of 46th Street and C Street.
Later it's at Pacific Highway, right next to the runway.
That's a distance of 4.6
miles. Next, we need time.
The plane crosses the first location at 8:32 in the video
and the second location at 10:12 in the video,
which is 100 seconds later.
Speed is distance divided by time,
so it's gone 4.6 miles in 100
seconds and that turns out to be
an average speed of 165 miles per hour.
Here's a second video from the same airport,
where the speed is about 144 miles per hour
using the same kind of math.
Next,  here's a video from LAX,
my home airport.
At 4:53 in the video the plane goes by a 
parking lot, and one minute later
it goes by the In-N-Out near the end of the runway.
That's a distance of 2.7 miles in one minute,
which averages to more than 160 miles per hour.
PS - if you've never been to In-N-Out,
you should try it sometime.
It's really good and it's right near LAX,
if you're ever flying through there.
Here's one last example using that same technique.
Here's the flight in a 747 at
cruise altitude and speed going across
Lake Tahoe, flying straight and level.
The point under that "i" in the logo
crosses 11.3 miles across the
whole lake in just 70 seconds.
And that works out to be 580 miles per hour.
Next I'm going to show you a second
technique with a stationary camera.
You'll need to have access to video
editing software where you can add a
timecode so you can measure individual
frames of the video.
Then you can calculate the speed of a plane from just
a second or two of footage,
though it's a bit harder.
Here's the Boeing 777 landing in Turkey.
Now it might look like it's going
the same speed as that bus,
but that's just because it's farther away.
You can get the speed by watching how
long it takes for the entire plane to
cross a particular point.
So remember: speed is distance divided by time.
So the distance in this case is the entire
length of the plane, and the time is 29 frames.
So it took 29 frames for that
plane to cross that distance.
So then you just do distance divided by time and
that turns out to be 170 miles per hour.
Here's another example of the Airbus A-380, the largest passenger plane in the world.
It passes a particular point in 32 frames
which is 1.067 seconds for a speed
of at least a 150 miles per hour.
Later on in the same video, there's an
A-380 flying at cruise altitude,
and that one is going much faster,
taking only 9 frames, or 0.3 seconds,
to travel its whole length,
which is a speed of 540 miles per hour.
Now, this technique is not super precise
because we're dealing with such short timescales,
but I think that we're within 10% of the right answer.
Finally, one last example: here's another A-380 flying at
about 440 miles per hour because it
takes 11 frames to travel its own length.
Okay, so there you have eight different
videos from six different people using
two different mathematical techniques to
show that planes really do fly pretty fast.
And I'm using just some basic math
with some basic measurements:
the lengths  of planes, and Google Maps...
Oh wait a minute!
The government is lying to us about the size of planes!?
And Google Maps is lying to us too!?
Well... if you believe that those are lies also,
then I don't know if there's much I
can say... but...
Yeah, I don't know what to say to that.
If you have any questions or comments, please leave them below.
If you have any suggestions about
how to improve the accuracy
of any of these calculations, I'd like to hear from  you.
And please be sure to like this video and subscribe
if you want to see some more stuff.
Alright, have a good day, talk to you later.
