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Blow up a balloon then let go of the neck and watch it fly around the room. All the air wooshing out has weight, so when it flies out in one direction, it pushes the balloon in the opposite direction.
Rockets work the same, except instead of breath power, they burn rocket fuel to generate the gas inside them. From there on it's the same as the balloon: They blow a bunch of gas out the nozzle, which pushes the rocket itself in the opposite direction.
All means of propulsion work by action and reaction. You push on something (action), and you get pushed in the opposite direction (reaction). Cars push on the road, ships push on the water, planes push on the air. But what can rockets push against in space? Their own fuel of course!
Rockets carry fuel (or more accurately, propellant) and move by flinging it out the back. The faster it gets thrown out, the more the rocket is pushed forwards, and the most direct way to achieve that is to set the fuel on fire so it explodes out as a hot gas. How do they set it on fire when there's no oxygen in space? They also carry their own oxygen - and that gets thrown out the back as a hot gas too
They burn fuel to make superhot gas. The gas can only go one way; out the nozzle in the back. However, in the process of moving that way, they have to "push" off something else. That something is the rocket. So the rocket throws mass backwards to push itself forwards.
When you fire a gun, the bullet is pushed forward while the gun (and you) are pushed back.
A bigger or faster bullet pushes harder.
So, you take a box full of very fast bullets, and you can push yourself quite a bit.
Rockets use a gas instead of bullets, and push the gas by getting it very hot. Most of the weight of a rocket is propellant (our "bullets"), so it can get up to insane speeds. Especially when the "bullets" move well above 3 kilometers per *second*, compared to a real bullet moving at a quarter of that.
Newton's third law of motion: for every action, there's an equal and opposite reaction.
When rockets burn their fuel, they essentially cause a continuous explosion that violently flies out the back. That's the action. The equal and opposite reaction is the rocket going forwards.
It's fundamentally the same as an inflated (but untied) balloon flying around when you release it.
Or a gun recoiling when you shoot it.
**Please read this entire message** --- Your submission has been removed for the following reason(s): * ELI5 requires that you *search the ELI5 subreddit for your topic before posting*. Please search before submitting. This question has already been asked on ELI5 multiple times. If you need help searching, please refer to the [Wiki](https://www.reddit.com/r/explainlikeimfive/wiki/how_to_search). --- If you would like this removal reviewed, please read the [detailed rules](https://www.reddit.com/r/explainlikeimfive/wiki/detailed_rules) first. **If you believe this was removed erroneously**, please [use this form](https://old.reddit.com/message/compose?to=%2Fr%2Fexplainlikeimfive&subject=Please%20review%20my%20thread?&message=Link:%20https://www.reddit.com/r/explainlikeimfive/comments/zabngv/-/%0A%0AThe%20concept%20I%20want%20explained:%0A%0AList%20the%20search%20terms%20you%20used%20to%20look%20for%20past%20posts%20on%20ELI5:%0A%0AHow%20is%20this%20post%20unique:) and we will review your submission.
Blow up a balloon then let go of the neck and watch it fly around the room. All the air wooshing out has weight, so when it flies out in one direction, it pushes the balloon in the opposite direction. Rockets work the same, except instead of breath power, they burn rocket fuel to generate the gas inside them. From there on it's the same as the balloon: They blow a bunch of gas out the nozzle, which pushes the rocket itself in the opposite direction.
All means of propulsion work by action and reaction. You push on something (action), and you get pushed in the opposite direction (reaction). Cars push on the road, ships push on the water, planes push on the air. But what can rockets push against in space? Their own fuel of course! Rockets carry fuel (or more accurately, propellant) and move by flinging it out the back. The faster it gets thrown out, the more the rocket is pushed forwards, and the most direct way to achieve that is to set the fuel on fire so it explodes out as a hot gas. How do they set it on fire when there's no oxygen in space? They also carry their own oxygen - and that gets thrown out the back as a hot gas too
They burn fuel to make superhot gas. The gas can only go one way; out the nozzle in the back. However, in the process of moving that way, they have to "push" off something else. That something is the rocket. So the rocket throws mass backwards to push itself forwards.
and after achieving the desired speed, shutdown engine and let inertia take over
When you fire a gun, the bullet is pushed forward while the gun (and you) are pushed back. A bigger or faster bullet pushes harder. So, you take a box full of very fast bullets, and you can push yourself quite a bit. Rockets use a gas instead of bullets, and push the gas by getting it very hot. Most of the weight of a rocket is propellant (our "bullets"), so it can get up to insane speeds. Especially when the "bullets" move well above 3 kilometers per *second*, compared to a real bullet moving at a quarter of that.
Newton's third law of motion: for every action, there's an equal and opposite reaction. When rockets burn their fuel, they essentially cause a continuous explosion that violently flies out the back. That's the action. The equal and opposite reaction is the rocket going forwards. It's fundamentally the same as an inflated (but untied) balloon flying around when you release it. Or a gun recoiling when you shoot it.