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Students build an apparatus that allows them to calculate the time it takes for an object to fall a certain distance and calculate acceleration due to gravity in the game world.

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Created by
Cameron Pittman


The Portal 2 - Education Version is a custom modification of Portal 2, the critically acclaimed single-player puzzle game from the developers at Valve. This modified version of Portal 2, along with a game called Universe Sandbox, is part of a program Valve is calling Steam for Schools (not to be confused with the STEAM education movement that shares the same name), in which they hope to encourage teachers to use their games to teach standards-based curriculum.
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Experience breakdown

Lesson Plan Overview

Time Needed: 60 minutes

Vocabulary: Gravity, Acceleration, Velocity, Displacement

Student Prerequisites: knowledge of gravity, decent algebra skills

Teacher Materials Needed: None

Student Materials Needed: Stopwatch, Microsoft Excel (optional, but recommended)

Standards: For a full list of standards covered in this lesson plan, please refer to this page.

In this lesson plan, students will be building their own experiment to calculate acceleration due to gravity in the game world. They will decide how to build an apparatus that allows them to calculate the time it takes for an object to fall a certain distance within the game.


A stopwatch/timer will be needed for this activity.

This lesson plan was developed with the idea that the educator understands physics and the basics of Portal 2. The lesson itself should flow from an introduction, into a main lab activity, and then finish with follow up questions and a homework assignment.

  1. The Introductory Activity section starts with questions to ask students at the beginning of class or in the class prior.
  2. The Implementation section gives instructions to the instructor as to how to set up the main lab activity.
  3. The Closing Activity section lists questions for students after they complete the main lab activity.
  4. The Homework section suggests questions to assign as homework after the lab.
  5. The Grading Advice section gives answers to all of the questions in the Introductory Activity, Implementation, Closing Activity, and Homework sections.
  • I’m always looking for better lessons or ideas. If you have any questions or comments, please contact me at: cameron *dot* w *dot* pittman *at* gmail *dot* com.
  • This lesson plan is meant to be a set of guidelines, not instructions. It is meant to be disassembled, reconfigured and reconstructed to fit your students and your teaching style.

Learning Objectives

  • Design a test that allows players to test the properties of gravity in Portal 2.
  • Demonstrate proper experiment design.

Lesson Steps

I. Introductory Activity

Displacement due to gravity is found through the equation: Δx = v1t + (½)gt2 (1)
Let's assume that, in a given situation, the initial velocity of an object is 0. Solve equation 1 for g.

II. Implementation

  • Instruct students to build an experiment in the game that allows players to test the strength of gravity.
  • Instruct students to build an experiment which easily allows them to reach three different heights repeatedly.
  • It will be easiest to use heights of 1, 2, 3 units above the ground, as shown below:

A sample experiment level.

  • For three trials at each height, students will need to use a stopwatch to calculate the time it takes them to fall to the ground (9 total measurements).
  • Students will record their data on the worksheet, which can be accessed here.
  • The class should share data by posting it on a blackboard/whiteboard.

III. Closing Activity

1. What was the most difficult part of testing gravity? What variable was the most difficult to account for?

2. Does the class’ data make sense? Why or why not?

3. Calculate gravity by taking the average of the class’ data [probably a good time for Excel]. Assuming each wall panel is 2 meters tall, how does gravity in the game compare to gravity on earth?

4. Is there a limit to the distance an object can fall in the game being used to test the strength of gravity? Why?

IV. Homework

Chell is on a platform 15 units above the ground. Using your data from class, calculate the time it will take her to reach the ground if she falls off the platform. Assume that g = 4.7 u/s2 and friction is negligible.

Grading aDvice

I. Introductory Activity:

Δx = (½)gt2 (2)

2Δx = gt2 (3)

2Δxt2 = g (4)

II. Implementation Grades:

  • To get an A: projects that easily allow students to easily and accurately measure both the time and distance of a fall.
  • To get a B: projects that are easy to perform but have high levels of uncertainty in measurements.
  • To get a C: projects that are not easy to perform and contain high levels of uncertainty.
  • To get a D: projects that do not allow players to test for either height or time.

The strength of gravity in Portal 2 is: g ≈ 4.7 u/s2.

III. Closing Activity:

1. Varies from student to student.Time will probably be the trickiest.

2. Everyone should get about 4.7 u/s2.

3. g = 4.7 u/s2 = 9.4 m/s2.

4. Yes. Once players start falling about 5 units, air resistance comes into noticeable effect.

IV. Homework:

Students should begin with the equation: Δx = (½)gt2. Rearranged, it easily becomes: (5) t =


Plugging in, using Δx = 15u and g = 4.7u/s2, we get that t = 2.5s.

Additional Activities

  • Students collect data using each other’s puzzles.
  • Students can build a puzzle around their gravity test.
  • Calculate error on class measurements.
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