Shadowing Practice: Why Earth Is A Prison and How To Escape It - Learn English Speaking with Video

We are prisoners on Earth. The Universe taunts us, by showing all the places we can't ever visit.

However, if our species wants to have a long term future, we have to escape our prison.

But what is keeping us here in the first place?

Turns out, we owe the universe a debt that is 4.5 billion years old.

Everything with mass in the universe attracts every other thing with mass.

We call this phenomenon 'gravity'.

The closer you are to a big chunk of mass, the stronger the attraction or the more you're pulled in.

This effect traps us on earth.

We can imagine this as being prisoners in a gravity prison, or a gravity well.

It's not a literal well, but a handy concept to understand how this works.

Being in a gravity prison means that you owe gravity energy.

But how can you owe energy?

Because in our universe, things don't want to change their speed or direction.

To convince them to move, you have to expend energy.

Billions of years ago, the gravitational attraction of trillions of trillions of dust particles orbiting our sun caught them together until they formed a planet.

This process used energy and created the gravity well we're now a part of.

The deeper you are inside the gravity well, the more energy you owe gravity.

If you don't find a way to get enough energy, then you aren't able to leave no matter what you do.

Because your atoms were once part of the dust that the universe expended energy on to get to this place.

Ok. Hmm...Let's summarise all of that again.

Objects in the universe don't like to move. You have to convince them to do so with energy.

Gravity used energy to convince the parts of our planet to move together.

This created a gravity prison in the process, trapping us .

To escape, it we need to repay it with energy.

Ok. How do we do that?

To get into space, we need to go through a complicated process of exchanging energy.

For this purpose, we build a negative potential energy repaying machine.

Known By their more boring name 'rockets' Rockets work by using some of the most energetic chemical reactions humans know about to basically explode fuel in a controlled way.

This converts chemical energy into kinetic energy.

The exhaust of the reaction is directed outwards, and pushes the rocket away from Earth.

By expanding a lot of energy, we are increasing our gravitational potential energy.

Which is a complicated way to say that we are paying back our energy debt to gravity.

But it's actually a lot trickier than that.

When you burn fuel to get into orbit, you lose lots of energy to heat, exhaust and atmospheric drag ,so you actually need much more.

And you can't just pile a huge amount of radioactive, really explosive, dangerous fuel close to your payload and detonate it.

You need a controlled burn which is complicated and makes your rocket very heavy ...which means it has more mass.

The more mass something has, the more energy you need to convince it to move, so you need more fuel to lift up your rocket.

But,if you need more fuel, that means you need more rocket to carry that fuel!

But, this makes your rocket heavier thus requiring more fuel which requires more rocket to carry that new fuel and so on.

At the end of this madness, you need closer to a 100x the weight of your payload to launch Ariane 6, for example will weigh 800 tons and should be able to transport 10 tons into geostationary transfer orbit or, 20 tons into medium earth orbit.

But a rocket can only produce so much thrust, so there is a maximum weight, after which it just won't take off.

If you add too much weight, it won't lift off. So, you can't just build bigger and bigger fuel tanks This is the tyranny of the rocket equation and it means space flight will never become easy.

But wait, it gets worse.

Getting to space is still not good enough- you're still inside the gravity prison at the edge of space and will crash back to Earth.

Staying in space is much harder than getting there.

To get to a stable position, where it can stay for a while, a rocket has to reach low Earth orbit.

To do this, you need a lot of kinetic energy which means going extremely fast at an altitude of about 100 km, this is 8 km/s 28,000 km/h is fast enough to travel around Earth in 90 minutes.

Here, we can use a trick.

Instead of flying straight up, we can go sideways!

Earth is a sphere.

So, if you're going sideways, fast enough the ground will curve away beneath you.

So, as long as you're above the atmosphere you'll be able to stay up there in orbit.

This is what the ISS does to stay fast enough.

If we look at orbits in scale, we see that near Earth orbit is laughably close to Earth.

To deploy, for eg Satellites, on leave for other planets, requires another round of energy debt repayment.

Getting to orbit is the most difficult part of space flight for us right now.

For example: If we want to send a rocket to Mars, half the energy is necessary just to get into orbit and the other half for the 55 million km to Mars.

Therefore, to be as effective as possible, rockets aren't built in one giant piece.

Instead, we use multistage rockets. We don't need to carry an empty fuel tank, so rockets drop it.

Rockets today, shed their boosters and main stage as they ascend with each successive stage being it's own fully contained rocket, complete with its own engine and fuel.

Ok. So this is why getting to space is hard.

If you feel all of this seems really complicated, don't worry. It's literally rocket science!

This video was made possible in part by a sponsorship by Airbus Safran Launchers and Arianespace.

Who are getting their new Ariane 6 rocket ready to launch into space in 2020.

You can learn more about the rocket here.

And as always, if you like what we do please consider supporting us on Patreon.com.

It really helps us out a lot!

If you're craving more space stuff now: here's a playlist for you.

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Word	Pronunciation	Meaning
rocket noun	/ˈɹɑk.ɪt/	A cylindrical projectile that can be fired to a great height through combustion, (specifically) a type of firework of this form, typically exploding with light…
gravity noun	/ˈɡɹævɪti/	Of an activity such as a ceremony, a person's conduct, etc.: the quality of being deeply serious and solemn, especially in a dignified manner; seriousness…
orbit noun	/ˈɔɹ.bɪt/	An elliptical movement of an object about a celestial object or Lagrange point, especially a periodic elliptical revolution.
complicated adjective	/ˈkɑm.plɪˌkeɪ.tɪd/	Difficult or convoluted.
convince verb	/kənˈvɪns/	To make someone believe, or feel sure about something, especially by using logic, argument or evidence.
ton noun	/tʌn/	The short ton of 2000 pounds (about 907 kg), 20 hundredweights of 100 pounds avoirdupois each.
dust noun	/dʌst/	Fine, dry particles of matter found in the air and covering the surface of objects, typically consisting of soil lifted up by the wind, pollen, hair, fiber…
trap noun	/tɹæp/	A machine or other device designed to catch (and sometimes kill) animals, either by holding them in a container, or by catching hold of part of the body.
prisoner noun	/ˈpɹɪzənə/	A person incarcerated in a prison, while on trial or serving a sentence.
attraction noun	/əˈtɹækʃn̩/	The tendency to attract.
exhaust verb	/ɪɡˈzɔst/	To draw or let out wholly; to drain completely.
repay verb	/ɹiˈpeɪ/	Synonym of pay back in all senses.
sideways adverb	/ˈsaɪdweɪz/	With a side to the front.
stable noun	/ˈsteɪ.bəl/	A building, wing or dependency set apart and adapted for lodging and feeding (and training) ungulates, especially horses.
trick noun	/ˈtɹɪk/	Something designed to fool, dupe, outsmart, mislead or swindle.

Word	Pronunciation	Meaning
go through verb		To travel from one end of something to the other.
lift off verb		Synonym of take off (leave the ground and begin flight).
lift up verb		To elevate to a higher position.
move together verb		for two climbers to attach themselves to the same rope and ascend at the same time without setting up belays.
pay back verb	/peɪ bæk/	To pay (a debt or the lender) so as to provide the entire amount of money owed.
stay up verb		To remain awake; to not go to bed.
take off verb		To remove.
turn out verb		To end up; to result.

Structure	In the video
Passive voice be + past participle — the focus is on what happens, not who does it	is directed · is complicated · aren't built
Relative clauses who / which + clause — extra information about a person or thing	burn which is · energy which means

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