logistics and momentum

I am started writing this during my planning period. We just finished the first part of the conservation of momentum lab (more on that in a moment). This was my first time doing a Portal 2 lab without prior access to our laptop cart because, well, this is the first time we’ve had the laptops in a cart. Before recently, they were stored in their original boxes and kept in my room. I had to move them to a cart so the whole school could have access, which is only fair, but I learned today that it takes a bit more preparation to make sure everything is up and running smoothly.

I received the laptop cart from the previous teacher a minute or two after class had started. As soon as my students finished their bell work, they picked up a laptop and opened Steam. At that point, they had to wait for me to come around and type in the Steam for Schools password. Then we started to run into issues. Different students tried signing on using the same username and began booting each other off Steam. For some students, it took a few tries to find a username that wasn’t already taken. (After today, I’ll be assigning students a specific username. Not sure why I didn’t think of this before.)

Some students turned on Steam only to find it needed an update (not a quick process on our ridiculously bad internet).

With limited connectivity in my classroom, some students lost their Steam validation after Portal 2 had launched, which led to some weird errors and unexpected game shutdowns.

Individually, none of the problems were a big deal. But troubleshooting 19 computers at the same time is a challenge, especially when I’m running a physics lab and helping students with the Puzzle Maker at the same time.

I let the lab progress until the last 15 minutes of class at which point I instructed them to sign out of Steam and log back in with a specific username. I gave each student an account number and had them log in with the option “Remember my password” checked. Now Steam automatically logs in.

I originally wanted to prevent Steam from automatically logging in on the school laptops. But this is a lot faster. Now anyone can play Portal 2 at any time without my permission, which, while potentially distracting for other classes, makes my life a lot easier. Our students are well behaved, though, so I’m not too worried that they’ll be playing without permission.

The conservation of momentum lab itself ran into issues. First off, it calls for cubes of varying masses. The problem here is that there aren’t any console commands to change the mass of cubes (yet). Instead, I substituted turrets for high mass cubes and spheres for low mass cubes. According to the game, normal cubes have a mass of 40 kg, turrets have a mass of 100 kg, and spheres (aka edgeless safety cubes) have a mass of 80 kg (Frankencubes are 50 kg).

Students will run into problems when they try using spheres, which roll around randomly. Any lab setups that require a stationary sphere quickly fall apart when the sphere rolls away. There are two solutions:

1) Boxing in the cube with light bridges.

2) Freezing time to keep the spheres frozen in place.

Option 1 is annoying and still never works right. Option 2 is slightly more complicated but works well.

How to freeze time:

1) Activate the console. Right click on Portal 2 in Steam. Click “Properties.” Click “Set launch options.” Type “-console” (without quotes) into the box that appears. Press OK and start up Portal 2. This only needs to be done once.

2) Make a level.

3) Press ` (the tilde key to the left of “1”) to open up the console.

4) Type “sv_cheats 1” (no quotes) and press enter. This only needs to be done once.

5) Type “phys_timescale #” (no quotes) where the # can be any number and press enter. The # will be a multiplier for how quickly time is passing. 1 makes time run normally, 0 makes it stop, 0.5 makes it run at half speed, etc.

Students can freeze time to keep spheres in place then run time normally to launch their experiment.

I also found students needed more instructions for making observations. They need to be reminded that they’re specifically observing changes in velocity, and as such need to identify both the speed and direction of movement of their objects pre- and post-collision.

Other than that, the lab went well. I’m still seeing a lot of enthusiasm for physics labs when we play Portal 2. The kids are trying hard even when they aren’t sure what to do or we’re experiencing technical difficulties.

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