Rockets! How Can We Change the Speed of a Rocket?

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Updated on Feb 11, 2012

Grade Level: 7th - 8th; Type: Physics


To determine how we can change the speed of a rocket.

Research Questions:

  • What is Newton`s Third Law of Motion?
  • What is the action force, the reaction force?
  • How does a rocket engine demonstrate Newton`s Third Law?
  • What is the law of conservation of momentum?
  • What is meant by the term balanced forces?
  • How does on determine the velocity of an object?
  • How does one determine the momentum of an object?

On the information level, this experiment serves to acquaint students with basic information on how Newton`s third law of motion explains how balloons and rocket engines work. For example, when you release the neck of an inflated balloon, the stretched rubber material pushes against the air contained in the balloon. The air rushes out of the neck of thee balloon. This action of the air rushing out of the balloon exerts force against the balloon, moving it in the opposite directions. In brief, Newton`s Third Law of Motion state that every action has unequal and opposite reaction. In the specific case of rockets, when we burn rocket fuel, we get hot gases. These gases expand rapidly as they are released from the back of the rocket. These gases produce our action force. The gases exert an equal and opposite force on the rocket itself, forcing the rocket upward. We speak of an action and a reaction force. The action force is force acting in one direction. The reaction force is the force acting in the opposite direction. In this project we are attempting to test whether we can change the speed of a rocket. We first need to define speed. We then need to accelerate or “decelerate” the rocket if we are to alter its speed. Therefore we need to define acceleration. Let us experiment with our balloons which will serve as our rockets. This is our task. Can it be done? Let us find out.

This science fair experiment also serves to acquaint students with the essential processes of sciencing such as the importance of the use of a control, of identifying dependent and independent variables, of data collection, of pictorial and or graphic presentation of data and of being able to make better judgments as to the validity and reliability of their findings. They take on the role of scientists and in the process they learn to act as one.


  • fishing line
  • scissors
  • balloons
  • tape
  • straws
  • meter stick
  • clock with a second hand
  • pencil
  • paper
  • copy of chart of observations

Experimental Procedure

  1. Gather the materials you will need for your project. These include: fishing line, scissors, balloons, and tape straws, meter stick, clock with a second hand, pencil, paper, copy of chart of observations. A camera ? For purposes of display of your project tor for inclusion in your final report for dramatic impact, you may want to photograph your procedure and results.
  2. Copy the chart for data collection of the speed measurements provided on the next page so that you can readily record your observations.
  3. Measure the room you are working in and cut the fishing line so that you can string it across the room. Attach one end of the fishing line to a chair or a table.
  4. Inflate the balloon.
  5. Using the tape attach the balloon to the straw. Placing the straw along the length of the balloon on its top side. Now deflate the balloon.
  6. Now, carefully thread the wire through the straw. Make sure that the neck of the balloon is facing you.
  7. Using your meter stick measure the distance from the end of the balloon to the place where the fishing line is attached. Record the distance.
  8. Inflate the balloon. With your fingers, pinch the balloon closed. Do not knot it! Hold one end of the fishing line. Get ready to release the balloon and to measure the time it takes to get to the end of the fishing line. Do It! Record the data.
  9. Calculate the speed of the balloon. Remember speed is equal to the amount of distance covered in a certain time namely distance /time (distance divided by time).Record the speed.
  10. Now, let some of the air out of the balloon. What you are doing is changing the mass of the balloonandrepeat steps 8 and 9. Record your data.
  11. Now, let us change the slope of the fishing line and again release the balloon and repeat steps 8 and 9 and determine its speed.
  12. Review your data. What did you discover? What was the impact on the speed when you changed the mass of the balloon rocket? What was the impact when you altered the slope of the line?
  13. Prepare your report. Make certain to include your research. If you have photos include them. Insert your bibliography. You may wish to take it a step further and state what you might to expand the research on this subject.

Charting the Data

Tests Change Made Distance in m Time in s Speed in m/s

Terms/Concepts: Motion, momentum, frame of reference, speed, velocity, acceleration, constant speed, average speed, mass, lower mass, volume and slope of the line.


Bernstein, L. Schacter, M. Winkler, A, Wolfe, S. Concepts and Challenges, Force, Motion and Work, Globe Fearon, 2004

Dr. Muriel Gerhard (Ed.D.) is a retired educator with fifty seven years of experience in all aspects of public education. She has been a teacher, principal, administrator, college professor, researcher, grants writer, change agent and science editor. She is the author of several books on education used as college texts. These include the best selling Effective Teaching Strategies with the Behavioral Outcomes Approach and The Behavioral Outcomes Handbook for Teachers and Administrators. Presently she is a consultant in science education and curriculum development, a marriage and family therapist, a newspaper columnist and an author. Her latest book, recently published, is a memoir of sixty vignettes entitled âNow That I`m Dead, I Decided to Write this Bookâ.