Dynamics Activity - Balloon Rockets1

(Conservation of Momentum Version)

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To design and build a balloon-powered "rocket" vehicle to travel down a string and back in the shortest time.

diagram of activity set-up


Your teacher will show you the "racecourse" for this activity, which is a string tightly stretched between 2 supports. (Practice and testing strings may be provided.)


  1. You may use only the equipment listed below.
  2. No parts (except air) may be added to your vehicle once it begins its trial.
  3. You must be able to attach your vehicle to the string without removing the string from its supports.
  4. You may not push (or pull) your vehicle at any time.
  5. The total length of your vehicle must be less than 2 meters.
  6. Your vehicle must start each trial not touching the string. The trip is completed when the vehicle:
    1. is attached to the string touching the first support, then
    2. touches the opposite support, then
    3. touches the starting support for the second time.




paper clips




  1. Draw a clearly-labeled sketch of each of your balloon rocket designs. If you change your design as you build and test your rocket, tell why you felt the change was needed and describe (or sketch) the change.
  2. Make a data table to hold your official time similar to the one below. Record your time(s):


    Time (seconds)





  3. Draw a diagram showing the momentum (vector) of your "rocket" and the momentum (vector) of the air. Be particularly clear about which "air" you are talking about.! How do these momenta compare? Why is it that the air being pushed out of the rocket moves faster than your rocket?
  4. If you had an opportunity to redesign your balloon rocket, what would you change, and why?

1based on Robinson, Conceptual Physics Laboratory Manual, Addison-Wesley, Activity 13, "Balloon Rockets"

last update December 26, 2005 by JL Stanbrough