[MUSIC PLAYING]
Hey everybody, it's me, Ben.
So today's question is, how
do satellites orbit the earth.
You'll see, we're
using this prop globe
that we use for everything.
But let's pretend there's
a satellite around it.
Satellites are, to some degree,
mysterious objects, right?
Orbital mechanics can
also be mysterious,
because there's
no easy way for us
to experience orbital
mechanics personally.
However, with a little
bit of imagination,
we can understand the idea
behind orbital mechanics
very easily.
So imagine what happens
if you throw a ball--
[CRASHING]
--and it goes 100 feet or so
and then it hits the ground.
That ball was actually orbiting.
It's just that the ball's orbit
is very, very, very short.
So let's say the
ball doesn't do it.
And you're like, Ben,
I've got this rifle.
I'm going to shoot that.
So you grab a
rifle, you shoot it,
and you fire it
straight and level.
A bullet might travel a mile
before succumbing to gravity
and hitting the ground.
So let's imagine another
thing, all right.
And we're just imagining stuff.
Let's say you had a very
large, powerful cannon,
and it's able to give
it's shell an extremely
high initial velocity.
So you're shooting this
cannon straight and level,
and the shell's going to
go many miles-- far enough
to actually follow the curve of
the earth for a period of time
before it hits the ground.
So one thing that gums up these
examples is air resistance.
Imagine if we took
this powerful cannon
to the moon, because
where else would we
take our imaginary
cannon, and we mounted it
on top of the biggest
moon mountain.
Well, the moon has
no real atmosphere.
It's completely surrounded
by the vacuum of space.
If we adjust the speed of
this cannon shell just right
and shoot it perfectly,
then the shell
would follow the curve
of the moon exactly.
It would fall at
exactly the same rate
that the curve of the
moon falls away from it.
So it would keep falling,
but it would never
actually hit the ground.
In fact, eventually, it would
curve all the way around
and, boom, ram right back
into the back of the cannon.
Now on the moon,
you can actually
have satellites in extremely
low orbit like that--
just a few miles off the
ground to avoid the mountains.
On Earth though,
it's not so easy,
because satellites have to
get above the atmosphere
and into the vacuum of space to
orbit for any length of time.
So 200 miles up is
about the minimum
that we'll need to avoid
atmospheric interference.
Let's take the Hubble
Space Telescope, right?
That's a popular one.
The Hubble Space
Telescope orbits
at an altitude of
about 380 miles.
But the principle here
is exactly the same.
The speed of the
satellite is adjusted
so that it falls to Earth
at exactly the same rate
that the curve of the earth
falls away from the satellite.
To put it in the most
simplistic terms,
it is perpetually falling.
It's just never managing
to hit the ground.
Thank you so much for watching.
We appreciate it.
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