Science- Physics

Balloon Rockets Lab

Research Question:Determine the work done and the power of a balloon rocket.
Assumption: the balloon rocket exerts an average thrust force of 0.5N.


Background Information: 

Work:  The action of a force to cause displacement of an object.

  • Unit: joules (J)
  • Work (J) = force (N) x distance (m)
  • When force causes a displacement = work (energy) is positive
  • When force hinders a displacement = work (energy) is negative
  • When force results in no displacement = no work

Energyability to do work/ to cause motion and change. It is neither created or destroyed but can be transferred from one object to another or transformed from one form to another.

  • Unit: joules (J)
  • E.g. Mechanical, elastic, gravitational, kinetic, chemical, thermal, sound, luminous, nuclear, radiant, magnetic, electrical, potential.

Powerrate of doing work or using energy

  • Unit: Watts (W)
  • Power (W) = work done (J)/ time (s) = energy used (J)/ time (s)

Free Body Diagram

A free body diagram for the forces acting on a balloon rocket on a string.

  • While we have released a balloon that is filled with air, the thrust energy that became apparent had caused the balloon to propel forwards. As the ballon is moving on the string (which is connected by a straw), friction is apparent between the two objects. But since the straw has a very smooth surface, the friction applied is not severe. Also, as the balloon moves from one end to another, air resistance on the balloon is shown.

Reaction Force Pair

A reaction force pair for the motion of the balloon rocket

  • When the balloon is blown up and is held at the tip, the air is trapped and is eager to get out for the object to return to its original shape. So, as the hand is released, the air forces itself out of the opening which enables the balloon to thrust forward.
  • Friction can be seem between the string and the straw, as the balloon rocket shoots from one end to another.
  • As the balloon is being held by the mouth, the air inside is wanting to push back out in order to form its original shape. When the balloon is released, both the air and the rocket balloon moves. This follows both Newton’s Third Law (“for every action there’s an equal and opposite reaction”) and the law of conservation of momentum (Jones, 2011).

Energy Transformation Taking Place

As the balloon is being blown and the tip is held, the air has no where to move. At this point, elastic potential energy is being stored in the balloon as it is being stretched out from its original shape. When the hand is released, the air has no where to go except for the opening in order to get back to its original position.So, when the mouth of the balloon is released, the elastic potential energy becames a kinetic energy and shows a thrust of force being released.

So, the overall forms of energy that are evident with the balloon rocket are; elastic potential, kinetic , sound, elastic, and thermal energy. The elastic potential energy is apparent as the balloon is inflated. The kinetic, sound, and elastic energy are evident when the balloon is released and thrusts forward on the string. The balloon shows thermal energy when it has stopped. The thermal energy can be seen between the string and the straw, as they create a low coefficient of friction and the weight of the balloon and straw is light, so the overall frictional force is effectively negligible (Jones, 2011).

Data Recording & Processing 

Controlled Variables: 

  • Size of the balloon
  • Length of string
  • Same balloon and straw used for every trial
  • Table 1:
  • Table 2:

Further Qualitative Data
  • Overall, a 30cm balloon is able to travel about 10m 89cm in just 2 minutes. The average work done was 5.45 joules and the mean of the power was 2.73. The work being done is twice as much as the power being made on the balloon.

Validity and Reliability of the data

  • The data is not reliable because we used a video instead of a stopwatch to record the time. So, the time calculated is not as percise which causes the calculations of work and joules to be less reliable. Also, for a few trials, the balloon had traveled all the way to the tip of the string which limits the balloon from traveling a distance it could actually go fully. As the balloon hits the end of the string, it would cause the balloon to stop at a invalid distance. The alternation between the distance the balloon traveled can be seen because of the balloon we have repeatedly used throughout the whole experiment. Because the balloon has been used several times, it has become more stretchy and easy to blow into than the first trial. According to the University of Illinois, the difference in the stretchiness causes a difference in the speed of the balloon. So, a balloon that is really hard to stretch out may move faster than a balloon that is easy to stretch, because it has a higher chance of pushing harder on the air. Although, we have performed five trials which was enough to be able to find the overall mean of the distance and time, and also to calculate the work and power seen on this balloon rocket.


 Efficiency: the ratio of useful work out from the total amount of work done, as a percentage (Taylor, n.d.)

  • Efficiency (%) = Useful work out (J)/ Total work done (J) x 100

This lab had enabled us to examine the overall work done and the power of a balloon rocket. As efficiency is the ratio of useful work out of the total amount of work done, the greater amount of energy transfers or causes the experiment to be less efficient. In this case, as there are more points in the balloon rocket run where energy is lost, the lab is not efficient. Some of those points can be seen as the balloon is let go and while it is in motion. As the balloon is released, energy is being exerted and also is being lost as it releases sound energy. Also, energy is being lost as it transfers into thermal energy as friction is revealed between the string and straw, as the balloon is traveling. The efficiency of the balloon rocket could be improved if the size of the straw is altered and a different string is used. With these suggestions, a shorter straw used and a smoother surfaced string would enable the balloon to experience less friction between the two objects. As there are less friction involved, the efficiency would be greater as there is a fewer amount of energy (both thermal and sound energy) being lost during the motion of the balloon rocket.

Further Research

The assumption used for the average thrust force of the balloon for this balloon rocket lab is 0.5N. But as we have calculated and researched further with the actual materials we have used, we see that this assumption is not valid. We found that the actual weight of the whole balloon rocket (the balloon, straw and tape) was only 3 grams. In this case, we could say the balloon itself has a mass of 3 grams because the straw and tape are extremely light and may not have altered the overall weight severely. With this data, the actual thrust force of our balloon rocket lab can be calculated using the formula for force (Force= mass x acceleration). The mass will have to be converted from grams to kilograms, 3grams to 0.003kg. So the mass of the balloon would be 0.003 kilograms and will be multiplied by the acceleration. In this case, I have calculated the velocity first for each trial which can be formulated by velocity = displacement/time. Then using those solutions, I would divide them by the time once again to get the acceleration (Acceleration = velocity/time). Then to find the force, I would take those acceleration solutions and multiply by the mass (0.003kg) to get the force. So the overall equation would look like this:
Force (N) = Mass of Balloon (kg)  x [(displacement(m)/time(s) / time(s)]
  • Table 3:
As shown in the table, the overall average force exerted from the balloon was about 0.01N. We can see that the assumption is too big in contrast to the actual thrust force. As we compare this actual thrust force of 0.01Newtons and the assumption of 0.5 Newtons, there is clearly a very different answer and we can conclude that the assumption is invalid. We can not always assume that the assumption of 0.5N is a good number to work with for the experiment.

Works Cited/ Bibliography (including in-text)

Self Assessment 

  • Criterion B: Communication in Science

Have a bibliography and cited all the sources.

  • Criterion C: Knowledge and Understanding in Science

Challenged myself to do the 5-6 questions on the assumptions of the thrust force on the balloon.


2 thoughts on “Balloon Rockets Lab

  1. HI Yurika!! 🙂
    I really like how you changed the color of the different things you will talk about. This helps make it easier to read and understand. I also like how you high-lighted your final number answers for each table you created. You also used images to describe the transformations taking place.

    I think your self assessment is very valid. I would have given you the same scores. You did very well in deciding which descriptors you completed and which you did not complete. If I were to grade this I would give you a 6 on criterion B and a 5 on criterion C. This is because you did not complete all the descriptors for the 5-6 level on criterion C. However, you went above and beyond the 3-4 ban.

    Good Job!! 🙂
    – Emily

  2. A good, well-presented piece of work. You have understood most of the content and have explained it well.

    “Overall, a 30cm balloon is able to travel about 10m 89cm in just 2 minutes. ” Ooops – there is some confusion here about units and the calculation, which could be avoided if the eqaution was written out in full. We use metres and seconds.

    You have used a range of sources, which are partly cited correctly. Other forms of communication are clear.

    The conclusions are valid, and you have made a good attempt at the conclusion.

    Well done. Grades are in Powerschool.

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