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Teaching Physics Blog

AP Physics:Is Momentum Conserved in Osmos?

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Learning Objectives
Students will design an experiment to determine if momentum is conserved in the video game Osmos.

Assessment Type
This activity can be used as a formative assessment, extracurricular project, or challenge problem for advanced students. There are multiple methods that could be used to answer the question. The ultimate goal is to promote student creative thinking and problem solving.

Assignment Details
  • Students should begin by downloading and installing the free demo of Osmos, which is available on a variety of platforms including Windows and Mac computers (http://www.hemispheregames.com/osmos/). Osmos is also available for purchase through the iTunes App Store for iPad, iPhone, and iPod Touch.
  • Students should experiment with the game to learn how it works. In particular, students should recognize how the conservation of momentum is essential to motion within the game. 
  • Students are challenged to answer the following question: Is momentum conserved when the mote propels itself? 
  • Students are asked to design an experiment to answer this question. In particular, they must clearly outline: 
    • The process they followed to reach their conclusions.
    • The data they collected
    • The assumptions they had to make.
    • The calculations they performed. 
  • Students should submit their solution in the form of a 2-page report or a 2 minute video. 

Instructor's Notes
  • In order to answer this question, students will have to wrestle with these additional questions:
    • How does the mass of the player mote compare to the mass of the expelled mote?
    • How can we determine the velocity of the motes?
    • Do we need to know the absolute velocity or will relative velocity suffice?
  • You may recommend that students use video analysis software to collected data on motion within the video game. By using a combination of screen capture software (such as Jing) and video analysis software (such as Tracker) students can extract numerical data to draw their conclusions.
  • A few well-timed screenshots could also be used instead of video analysis to measure the recoil of each mote and ultimately answer the question. 
  • The following could be used as a simple rubric for evaluating this student project:
  • (10 pts) - Process for solving the problem is clearly outlined and accurate
    (5 pts) - Assumptions are appropriate and data is collected
    (5 pts) - Calculations are accurate and solution is correct.

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NIST Reference on Constants, Units, and Uncertainty:
AP Physics B Site from Dolores Gende, AP Central's content advisor for physics since 2004:
College Board's AP Physics C: Electricity and Magnetism Course Home Page:
College Board's AP Physics C: Mechanics Course Home Page:

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