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Grade Range
Grades 6–8
Group Size
2-4 students
Active Time
30 minutes
Total Project Time
45 minutes to 1 hour
Area of Science
Key Concepts
Newton’s laws of motion
Standards
NGSS
This lesson plan aligns to these NGSS standards:
  • MS-PS2-2
Florida
This lesson plan aligns to these Florida standards:
  • SC.6.P.13.3
Texas
This lesson plan aligns to these Texas standards:
  • 112.18.b.8.B
  • 112.20.b.6.C
Two stage balloon rocket

Overview

Learn about real space flight and Newton's laws of motion with this fun project! This new twist on a classic project lets your students build a multi-stage balloon rocket that they can launch across the classroom. Show this video to your students to introduce them to the project:

Credits

Ben Finio, PhD, Science Buddies
This lesson was inspired by the Balloon Staging activity from NASA.

Materials


Materials per group of 2–4 students:
  • Modeling balloons (2), available from Amazon.com. These are the long, skinny kind of balloons used to make balloon animals. Have some extras ready in case some balloons pop.
  • Balloon pump (included with the balloons from Amazon.com, can be shared among multiple groups)
  • Milkshake straws (2), available from Amazon.com
  • One inch section cut from cardboard paper towel tube
  • Fishing line or smooth string, available from Amazon.com (one spool should be enough for entire class)
  • Large binder clips (2)
  • Clear tape or masking tape
  • Scissors

Learning Objective

  • Learn about Newton's laws of motion and how they apply to rocket flight
  • Learn about real multi-stage rockets and how they save energy when launching payloads into space

Science Concepts

A classic "balloon rocket" project uses a single balloon taped to a straw and attached to a piece of string. When you inflate the balloon and then release its nozzle, air is expelled out the back of the balloon. According to Newton's third law of motion (for every action there is an equal and opposite reaction), this means the balloon is pushed forward along the string. Friction between the string and the straw acts opposite the direction of motion. The balloon's acceleration depends on its mass and the sum of these forces (Newton's second law, force = mass × acceleration).

Newton's laws and a balloon rocket

This lesson expands on the traditional activity by adding a second stage to the balloon rocket, modeled after how real rocket launches work. It takes an enormous amount of energy (and therefore, fuel and money) to send a payload into space. In a two-stage rocket launch, the first stage lifts the rocket through the initial phase of its flight. Then, after its fuel is depleted, it breaks away and falls back to earth, while the second stage continues its flight. This saves energy because the depleted first stage is not carried all the way into orbit, allowing the second stage to travel farther with less fuel.

Diagram of a two-stage rocket launch

Building the Rocket

Watch this video to familiarize yourself with the activity. You can also show this video to your students:

Note: a printable PDF of these instructions and a PowerPoint® presentation you can use to walk your students through the activity are both available for download in the Teacher Tools section.

  1. Cut a piece of fishing line long enough to stretch across the room, with enough extra to tie it on both ends.
  2. Thread the fishing line through two straws, pull it tightly across the room, then secure it at both ends (for example, tie it to two heavy pieces of furniture).
  3. Cut a small ring (slightly less than one inch long) from the paper towel tube.
  4. Stretch the balloons to loosen them before inflating.
  5. Inflate one balloon about 1/2 to 3/4 full. Do not inflate the balloon so much that it starts to bend significantly. Use a binder clip to pinch the balloon's nozzle shut so it doesn't deflate.
  6. Pull the balloon's nozzle through the cardboard ring, keeping it clipped shut.
  7. Thread another balloon partially through the cardboard ring. Make sure its nozzle is facing the same direction as the first balloon. Note that the first balloon you inflated will be the second stage of your rocket, and vice versa.
  8. This is the hard part; be patient! Inflate the second balloon such that it presses up against the inside of the cardboard ring, squeezing the nozzle of the other balloon shut (see diagram). You should be able to remove the binder clip from the first balloon and have it stay inflated. This may take a few tries; if you have problems getting the first balloon to stay inflated, see the Troubleshooting section.
    lesson plan question mark What do you think will happen when the first stage deflates?
    lesson plan conversation bubbles The inflated first stage is pressing on the nozzle of the second stage, keeping it shut. When the first stage deflates, this will allow the nozzle of the second stage to open and air will escape.
  9. Use a binder clip to pinch the nozzle of the second balloon shut, and tape the balloons to the straws. Make sure the balloons and straws are pointed in a straight line.
    lesson plan question mark What do you think will happen when you release the nozzle of the first stage? Why?
    lesson plan conversation bubbles When you release the nozzle of the balloon, air is pushed out the back, which pushes the balloon forward (Newton's third law). This propels both balloons forward along the string. Eventually, the first stage deflates enough that the nozzle of the second stage opens. The second stage is then propelled along the string while leaving the empty first stage behind, just like a real rocket.
  10. Pull the balloons to one end of the fishing line, and remove the binder clip from the first stage. What happens?
  11. To reset your rocket, repeat steps 5-10.
    lesson plan question mark Did your rocket work perfectly on the first try? Why or why not? If something went wrong, how can you fix it?
    lesson plan conversation bubbles Many students may find that their rockets do not work perfectly on the first try. This is OK! Learning from your mistakes and trying again is something that real-world scientists and engineers do every day. See the Troubleshooting section for some tips about getting your rocket working.
Assembly instructions for two-stage balloon rocket

Troubleshooting

It can be hard to get your rocket to work on the first try—don't get frustrated! You might need to adjust how much you inflate the balloons, how far you push them through the cardboard tube, and where you tape them to the straws. If you have trouble getting the first balloon you inflate to stay sealed, try keeping its nozzle pinched shut with a binder clip until right before you launch your rocket, or twisting the balloon a couple times to help seal the nozzle:

Pinching shut the nozzle of a balloon rocket.

Do your best to make sure the balloons and straws remain in a straight line. If the balloons are curved or not aligned with each other, this will introduce extra friction along the fishing line and slow your rocket down. Stretching the balloons before you blow them up will help them inflate evenly instead of curving. Also make sure the balloons' nozzles are pointed along the fishing line, so the balloons are pushed forward when the air escapes. If the nozzles are pointed sideways, they will not push the balloons forward (remember Newton's third law!). You may need to experiment with the best location to tape the balloons to the straws, and you can also try taping the cardboard ring to one of the straws.

Aligning the balloons and string of a balloon rocket

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Grade Range
Grades 6–8
Group Size
2-4 students
Active Time
30 minutes
Total Project Time
45 minutes
Area of Science
Physics
Key Concepts
Newton’s laws of motion
Standards
NGSS
This lesson plan aligns to these NGSS standards:
  • MS-PS2-2
Florida
This lesson plan aligns to these Florida standards:
  • SC.6.P.13.3
Texas
This lesson plan aligns to these Texas standards:
  • 112.18.b.8.B
  • 112.20.b.6.C