## one week of teaching with portals

Here are three student made levels from the first week of playing Portal 2 in physics. You’ll see they’re simple with extraneous objects and obvious objectives, which isn’t surprising given that they had only played about two hours of Portal 2 before making these. To be clear, these weren’t for any particular experiment in class. Students made these as first attempts at making puzzles.

It’ll be interesting to compare these novice levels to what they make after they familiarize themselves with Portal 2. I’m excited to see how they progress.

Overall, I’ve seen some interesting reactions from the kids. For the most part, they seem pretty enthused. They’ve been explicit about how they appreciate applying what we learn in lecture to what they can do in the game. I even had a student tell me that she enjoyed using math for the first time when she used data from her own experiments to calculate the strength of gravity. Students have made comments about how engaging physics lessons are with the puzzle maker, and I’ve had numerous kids tell me they’re looking forward to physics class, which makes me feel pretty good!

So far we’ve run through a few labs where they’re building really simple experiments in the puzzle maker.

In this lab, students are measuring the distance and time of a fall to calculate the strength of gravity in-game. The students who fell the farthest measured the most accurate measurements so far. Without an in-game timer, students have to use a regular stopwatch to calculate the time of their falls. Unfortunately, they aren’t the most careful bunch and tend to be off by a sizable fraction of a second each measurement. That kind of error wreaks havoc on measurements when the fall time is only about half a second anyway. They need a long fall time to minimalize issues from their reaction times.

Class average:

5.3 panels/s^2 (actual value: 4.7 panels/s^2)

In this lab, students are calculating terminal velocity by measuring time and distance as they fall in an infinite loop. They then repeat their experiment with a cube. When I originally wrote this lab, I hadn’t considered the idea that portals could impact velocity. Since then, I’ve found that portals slow objects down, which almost makes this lab pointless. However, I still taught it as practice for data collection and to identify that cubes are subject to a bit more friction than players (I think). Either way, this lab easily led into a useful discussion about the effects of friction and air resistance.

Class 1 averages:

Chell: 10.8 panels/s          Cube: 9.8 panels/s

Class 2 averages:

Chell: 10.8 panels/s          Cube: 10.8 panels/s

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## success!

I’m feeling really good right now. After about a year of work, I finally got a full class of students playing Portal! My physics students played Portal 2 for an hour in class yesterday. On Friday, they’ll be doing their first lab (on gravity). Keep an eye out this weekend for some student made experiments!

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## Whoops part 2

If you remember from last time, I calculated the amount of work being exerted by an aerial faith plate, then used my answer to calculate the distance a projectile would fly. I asserted that if I could predict where the projectile would land using the amount of work being done, then work is a measurement that is actually conserved by an aerial faith plate. The only problem is that in calculating the initial velocity of a projectile off an aerial faith plate, equal masses cancel out. Equating work to kinetic energy and solving for velocity, we find that:

v = √(2*W/m)

and given that

W = m*a*d,

we actually have

v = √(2*m*a*d/m)               [bolded for emphasis]

And if the two masses are the same, they cancel out. So last time when I correctly predicted the distance my projectile would travel, I erroneously claimed that I was able to do so because that work done by aerial faith plates was conserved. It was actually because my calculations cancelled out mass, so being able to calculate the distance my projectile traveled had nothing to do with work.

So, I reran the experiment, this time with a weighted sphere, which, according to the game, has a larger mass of 75 kg. Plugging in to the equations above and running the same experiment as last time, we find that the weighted sphere should travel about 5 panels if the aerial faith plate enacts the same amount of work on any object it launches. As you can see in the video below, that clearly doesn’t happen.

Work done by the aerial faith plates isn’t conserved. It appears as if they ignore the mass of an object and so subsequently calculating the amount of work an aerial faith plate exerts isn’t useful. It appears they use a different factor to determine the path a projectile will take, which will be investigated soon.

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