Newton's Laws: Making Simple Rockets

“Begin countdown to liftoff – 10,9,8,7,6,5. . . We have main engine start . . . 2,1,0 . . . SRB ignition ---- We have LIFTOFF!”

Amidst the cheering throughout Mission Control, the space shuttle rises off the launch pad, completes its roll maneuver, and thus begins its fantastic voyage into low-Earth orbit. There, astronauts will complete their mission of repairing a damaged solar panel on the International Space Station, and conducting biomedical experiments to determine the effects of weightlessness on the human body. Thousands show up to watch the launch, and many more sit transfixed in front of their televisions as humans once again defy the laws of gravity and enter the harsh environment of space. As they observe, most people probably don’t consider the scientific principles that allow this amazing feat to take place.

On a basic level, rocketry can be explained using Newton’s Three Laws of Motion. In layman’s terms, the first law states that something that’s moving will continue to move in a straight line until something stops it or changes its direction. The same thing applies to objects that aren’t moving. In other words, once a spacecraft goes into space, we don’t need to use any fuel to keep it moving. Without air resistance, friction, or other forces to slow it down, it will continue to move at the same speed and direction without additional propulsion.  This saves a lot of fuel on a voyage to Mars!

Newton’s Second Law simply stated says that the more mass and acceleration an object has, the more force it has (F=m*a). This means that a rocket headed to low-earth orbit requires an engine that burns a large mass of fuel, and pushes the resulting gas out of the engine as rapidly as possible. In other words, the greater the mass of rocket fuel burned, and the faster the gas produced can escape the engine, the greater the thrust of the rocket.

Finally, Newton’s Third Law states that every action has an equal and opposite reaction. When the fuel is burned, and the resulting gas escapes the engines, this provides the action. The reaction is the rocket moving in the opposite direction. You can easily illustrate this with a balloon by blowing it up and letting it go – as the gas escapes the nozzle, the balloon will fly in the opposite direction!

You can have your students illustrate these ideas with very simple materials: a film canister (the kind that seals on the inside), antacid tablets, construction paper, and tape. Once they have had some time to experiment, I ask them to write me a brief essay explaining how Newton’s Laws relate to their “rockets.”

Directions for students:

1. Build the body of your rocket out of construction paper. Experiment with different lengths of body tubes to determine which might be best.
2. Design fins for your rocket.  Fins are used to maintain stability and keep the rocket flying straight. They come in many different shapes and sizes, so experiment with your design to determine the type and number of fins that are best.
3. Make a nose cone for your rocket by cutting out a circle and cutting a pie-shaped wedge out of it. Fold your circle into a cone shape and tape it in place.
4. Decide on a name for your rocket and write it on the side of your design.
5. Get your rocket ready to launch by placing half an antacid tablet in your film canister.  The canister should contain some water – you can experiment to determine the best amount to add. 
6. Quickly snap the lid on the canister and place it lid-side down on the ground. Wait for launch!
7. Experiment with lots of different designs and different amounts of water. Remember to change only one thing at a time. Otherwise, you won’t know which change caused a different effect. Good luck!

For more ways to teach Newton’s Laws, check out the following lesson plans.

Newton's Laws and Rocketry:

Rockets on a Shoestring Budget

Students, working under budget constraints, build pop-rockets and then launch them. Students still work in pairs to complete budget worksheets, and use their "Blast-Off Bucks" to pay for the construction. Students then redesign their rockets and launch them again with the engineering improvements they have made.

TE Activity: You're a Pushover!

Students learn about Newton's Third Law of Motion. They discuss how this law applies to thrust in aircraft. In this lesson students work on activities and worksheets that reinforce that for every action there is an equal and opposite reaction.

Action-Reaction! Rocket

Students use a balloon and a guide string to design a rocket. They use this model of  a rocket to learn about Newton's three laws of motion. Then students look at the effect different forces have on the motion of a rocket. As part of this lesson students measure the distance a balloon travels along a string to show reaction force. They collect and analyze data about how far balloons of different size travel along a sting. Then students graph the results.