50 Years On From The Apollo Moon Landing: But How Do Rockets Even Work?

Updated: Sep 3, 2019

#physics #space #rocket #forces #newton #physics #motion

It was on the 21st July 1969 that American astronauts Neil Armstrong and Buzz Aldrin were the first people ever to set foot on the moon. They had embarked on a journey that lasted them 8 days, 3 hours, 18 minutes and 35 seconds and would change the world forever. People everywhere were captivated by the tales of these brave astronauts as they laid the groundwork for many to come; proving to everyone that the dream to venture further into the unknown depths of our universe was as relevant as ever.

50 years on, with space travel having developed so much, does the average person actually know how a rocket works?

It's not rocket science! Oh wait... It is...

We've probably all drawn a rocket at some point in our lives, and it's pretty certain that you've seen a picture of one. But have you every thought about how exactly it goes up?

You can only every move something in three ways: it can be pushed, pulled or twisted. These movements are caused by forces. There are different types of forces, that work in different ways, but they all do one of those three things. Every movement you can imagine in your body or of any object happens because of a combination of these forces.

When you move your arm, the muscles in your arm move to push, pull or twist it.

Anyway, back to rockets, how do you think rockets move upwards?

Give it a think - here's a picture to help you imagine it. Think about what pushes the rocket upwards and how that push works. What does it push against? What causes the push? When and how does it stop pushing?

If you look at the picture, you'll see lots of fire coming out of the bottom of the rocket. This comes from the engines on the rocket. When the engines are switched on they push really hot air out of them - that's what causes the fire you see.

Why do you think the hot air pushes the rocket up?

Maybe the hot air pushes against the air that's already there and that's what pushes the rocket up?

That's very very close to what actually happens, so if you thought that - well done. However, it's not the whole picture.

Basically, whenever you push something, it always pushes back. This was a law of physics that was first noticed by physics legend Sir Isaac Newton. It may sound weird, because you never feel stuff pushing you back, but the world wouldn't work without it.

Imagine you were swimming front crawl (or the doggy paddle) and you push the water under you away. If that water didn't push back - you wouldn't move! You'd just move the water away but you wouldn't be pushed forward. What actually happens is, you push the water back and the water pushes you forward. The harder you push the water, the harder it pushes you back. This is why we say "every action has an equal and opposite reaction" - every time you push something, it pushes you back the same amount. This is called Newton's third law of motion.

Again, back to the rockets: can you apply the principle that "every action has an equal and opposite reaction" to the hot air coming out of the rocket?

Give it a think...

Final Answer: What happens is, when the engine blows out hot air - the hot air also pushes the rocket up because there is an equal and opposite reaction from the hot air. This acts on the rocket and the rocket can blast off into space!

The red arrow is the reaction and the green arrow is the equal and opposite reaction from the hot air -this pushes the rocket upwards.

This is a really hard concept to get you head around - it's very complicated. But try thinking about other ways where Newton's third law of motion happens in real life.

Did you know this? What other questions about rockets or space do you have? Do you want to know more about how engines work? Or maybe what's in space?

Get in touch!


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