what if Earth and Mars switched places?

Why can't planes fly to space?

That's a great question

All of the astronauts who go to space get there

using a rocket, and yet airplanes do go really high.

So why don't we planes to get to space?

To figure this out, we need to know more about

how a plane flies at all.

I promise once you understand how an airplane flies,

I think you'll be able to easily figure out

why airplanes can't fly to space.

So we'll come back to the question of space at the end.

First, let's talk about how an airplane flies at all,

and when you stop and think about that,

it's actually pretty amazing, isn't it?

Think of just how heavy an airplane is.

Why wouldn't it just fall out of the sky?

There's a clue, and it's something

you have to try for yourself.

Next time you're in a car going fast like on the highway

and the windows are down, try holding your hand out.

But not just sticking your hand straight out,

instead at a tilt like this.

Now obviously you wouldn't want to stick your hand out

if there's cars very close to you going past,

make sure your parents are supervising, but give this a try.

If you've ever tried this before, you'll feel what happens.

As soon as you tilt your hand, it starts to get lifted up.

What's going on here?

Why does tilting your hand make it suddenly start to lift?

What do you think?

Here's the thing to notice.

When you put your hand out the window, at first if you

have it straight like this,

 air just goes around your hand.

But as soon as you tilt your hand,

now some of that air bounces off your hand this way,

pushing your hand up as it does.

You may not have any experience flying an airplane,

but it's the same basic idea when you fly a kite.

Notice how a kite too is tilted.

If it's a windy day, the air hits the bottom of the kite,

and bounces off the bottom lifting the kite

up off the ground.

That's what makes a kite fly.

So next time you see an airplane, have a look.

What do you notice?

The wings are tilted.

Of course being tilted alone isn't enough.

There has to be wind that's hitting the wing.

Each time a gust of wind comes by it lifts the plane up.

It's the tilt of the plane's wings that pushes the wind

downwards lifting the plane off the ground.

Now obviously when you wanna fly in an airplane,

it's not that you just have to sit there

and wait for a windy day.

So what if there's no wind?

Well it's helpful to think again of flying a kite.

On a day with no wind, you can still make the kite lift up

by running along the ground.

By running, that pushes the kite forward through the air.

What you're doing is creating wind that hits the kite.

Well a plane is no different.

It doesn't have to be a windy day to fly.

That's what a plane's engines do.

A plane's engines constantly push the plane

forward through the air.

They create wind that hits the tilted wings.

Because the wing is tilted, as the air hits it,

it pushes up on the plane.

But what about the fact that planes are so heavy?

This Boeing 747 for example weighs the same

as 50 elephants.

The amazing thing is there's really no limit

to the amount of weight that can be lifted,

as long as the engines create a strong enough wind.

Now you can understand why airplane can't fly to space.

The higher up you go to earth's atmosphere,

the less air there is.

By the time you reach space, there's no air at all.

Even if a plane had the most powerful engines in the world,

those engines are useless if they're not

pushing the plane forward through air.

So the name airplane really is a great name for what it is.

Airplanes can't stay up in the air

without pushing air downwards.

Just so you know, the tilted wings of most large airplanes

is definitely not the only way to push air downwards.

There are other types of wing designs that can do this too.

But all of them work using the same basic idea.

That's all for this question.