# How Rockets Work

To understand rockets, you need to know Newton's laws of motion:

1. An object will remain still or keep moving the way it's already moving until some force changes its movement.
2. Force equals mass times acceleration (f = ma).
3. For every action there is an equal and opposite reaction.

The first law makes it obvious that a rocket won't move until some force starts the movement. We don't actually need to worry about that law too much.

Let's go to the third law: "For every action there is an equal and opposite reaction." This means that if you apply a force in one direction, an equal amount of force will be applied in the opposite direction.

Imagine a balloon filled with air. If you open the lip and let the air out, the air will accelerate out of the balloon, in whichever direction the lip is pointed. That's the action force. The reaction force is the balloon accelerating in the opposite direction.

If the lip is facing down, the balloon will accelerate upwards (actually in practice you'd need a stick attached to the balloon to stabilize it and keep it flying straight).

All rockets use the same basic principle: Shooting fuel out the bottom end will make the rocket move up. Rockets need a lot of force. This is where Newton’s second law of motion comes in: Force equals mass times acceleration (f = ma). This means that if you want more upwards force you need to shoot out more fuel, or you need to accelerate that fuel more. Rockets accelerate the fuel by burning it, so it shoots out at very high speed. The biggest, fastest rockets are the ones that can push out the most fuel with the greatest acceleration.

Rockets need four main things to be useful:

1. The payload is the thing you want to get into space. It is usually a spacecraft of some kind, containing people, scientific instruments and/or supplies. Note that the payload is usually only a small part of the whole rocket system.
2. The control system guides the rocket and keeps it on course.
3. Fuel is the bulkiest, heaviest part of almost all rockets.
4. The engine is where the fuel gets burned and accelerated out of the nozzle at the bottom of the rocket. It is common to have multiple engines in a single rocket.
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