Now the question is: what do these laws have to do with rockets? As it turns out, rockets rely on them to move forward through a process called propulsion. This process begins with the rocket’s fuel source. A good fuel contains a large amount of stored chemical energy, which is released through a process called combustion—something we’ll explore in more detail later in our engineering lesson. For now, you can understand combustion simply as another term for burning something, in this case, our fuel source.
A simple Campfire is an example of a combustion reaction!
Image Credit: Britanica https://www.britannica.com/science/combustion/History-of-the-study-of-combustion
When fuel is burned through combustion, exhaust gases such as methane and carbon dioxide are produced. Rockets move forward by allowing these gases, which are extremely hot and thus are traveling extremely fast, to flow out of the rocket through an opening at the back end, called the nozzle. This is where Newton’s third law comes into play! As the fuel flows out of the rocket (the action force), it exerts an equal and opposite force on the rocket, which pushes the rocket forward (the reaction force).
Video Resource: How do combustion and propulsion work?
Watch the following video and answer these questions:
What is a combustion reaction? How are they used to power rocket engines?
What is the “Fire Triangle” and why is it important?
What is the importance of the rocket nozzle in propulsion?
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Newton’s second law is just as important for understanding rockets. Rockets are enormous, weighing up to 2.34 million pounds. To put that in perspective, that’s about the same as 1,000 fully grown elephants. Because rockets are so huge, they also require a massive push in order to speed up enough to get off the ground. Therefore, rockets must burn huge amounts of fuel in order to get into the air and reach space.
Image 2: NASA. (1992). STS-45 Atlantis, OV-104, lifts off from KSC Launch Complex (LC) Pad. NASA Image Gallery. Retrieved 2025, from https://images.nasa.gov/details/s45-s-055.
But here’s the problem: fuel itself is heavy. The more fuel you add, the heavier the rocket becomes—and at a certain point, adding extra fuel can actually reduce performance because the rocket becomes too heavy to launch efficiently (again, due to Newton’s second law). This creates a major challenge for rocket engineers. Even modern liquid and solid fuel sources do not produce enough thrust per pound to allow for quick and efficient travel to deep space. The voyager missions, for example, have taken decades just to reach the outer edges of our solar system. Current methods of propulsion are thus extremely limited in their capacity for efficient space travel.
As we will see in our engineering lesson, rocket engineers have attempted to find solutions to this problem, such as building rockets in stages that can be discarded to reduce weight and maximizing rocket efficiency to try to squeeze out every last bit of energy from the fuel. However, in order to truly make way for interstellar travel, entirely new means of propulsion are likely necessary.
The above image is a NASA Figure showing breakdown of rocket weight between propellants and engine parts found at https://forum.nasaspaceflight.com/assets/50972.0/1915525.jpg. The most striking thing about this graphic is just how little the actual structure of the rocket itself contributes to the overall weight. Remarkably, over 90% of any rocket's pre-takeoff weight is simply propellant. This is why simply adding more and more fuel is an inefficient way of reaching further into space: fuel is just so heavy and so difficult to lift off the ground.
Video Resource: Fun with Model Rockets!
If you’d like, you can watch the following video of a dad and his son building and launching their own model rocket—a heartwarming moment that also perfectly demonstrates Newton’s 3rd law in action, just on a much smaller scale than a full-size rocket. My 6yr Old and I Designed and Built a Rocket
Finally, check out Estes Rockets if you would like to build your own model rockets!!!!!! https://estesrockets.com/?utm_medium=ppc&utm_source=adwords&utm_term=estes 
