Monthly Archives: August 2012

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.

Gravity Lab:

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)

Terminal Velocity Lab:

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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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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an even closer look at air resistance

I took a deeper look at my experiment from the last few posts and made a couple graphs.

The first details the difference between predicted and actual values for the magnitude of the cube’s velocity as it flies through the air:

Notice how the actual data strangely has a small dip at the beginning. I’m not sure where that’s coming from. Let’s take a look at its X and Y velocities:

The predicted values run a little bit farther than the actual values because I let my simulation (i.e. Excel formula) run a little bit longer than it takes for the cube to hit the ground.

There seems to be a weird jolt around 0.2 s. I’m not really sure what’s going on here. If you’ve got any ideas, please let me know.

I also looked into the difference between predicted and actual values for the height of the cube as it flies through the air:

I had to eyeball the height of the cube as it fell, which led to the wonky graph line. Regardless (and unsurprisingly), it still appears as if it takes a little bit longer for the cube to hit the ground than is predicted. It’s safe to assume that this is because of air resistance.

Any ideas about what’s going on here? Any ideas for new tests? Let me know!

I apologize for the dearth of posts lately. School started this week (!) so I’ve been insanely busy. I’m planning on giving my students their first hands-on experience with Portal 2 in about two weeks. They’ll be running labs that have been almost a year in the making. Of course, anything and everything that happens with portals in class will be documented here. Stay tuned.

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