In about 5 minutes, one of my students figured out a clever way to make an in-game timer using linked buttons and cube droppers.
Interestingly, the student who made it has poor communication skills. I had trouble following his explanation of what he had in mind, yet he clearly knew what he was talking about. The Puzzle Maker gives students like him the opportunity to show what they know in a totally unique way, that is, for some students, more natural than traditional communication.
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.
Of course, immediately after I finish a video I realize that I came to an incorrect conclusion. For the fun of it, I’ll post what I was working on below. See if you can figure out where I was wrong (answer after the video).
“We could be wrong…”
If you break down the equations, you’ll actually discover that mass cancels out when calculating the initial velocity of the projectile. In other words, mass doesn’t actually matter. This experiment explores the way in which the Source engine handles an aerial faith plate’s acceleration and velocity more than it does mass. Mass easily could have been arbitrarily high or low and it wouldn’t have affected our results. Unlike what I said in the video, this experiment does not show that mass is an internally consistent variable. Whoops. However, this video does a good job of showing how well Source handles projectile motion, so I’m posting it for now. Expect a follow up with objects of varying mass.
sv_cheats 1 (only needs to be done once)
noclip (lets you fly around the room)
phys_timescale 0 (freezes objects in the game)
phys_timescale 1 (lets objects move normally again)
impulse 200 (removes/replaces portal gun)
Welcome to everyone from Teach with Portals and Wired’s GeekMom! It’s great to have you here! If you get any ideas or have any questions while you look around the site, I’d love to hear from you. Feel free to email me (cameron *dot* w *dot* pittman *at* gmail *dot* com) or just comment right here.
I’m working on another video right now. Check back later this evening to learn about W=Fd and means of testing the game’s internal consistency.
Edit: And it looks like EnGaming is linking to the Wired article. Hello EnGaming!
Portal 2 can help students study more than just mechanics.
Thanks again to Yasser Malaika from Valve for sharing this awesome demonstration of the ideal gas law made using the Puzzle Maker. If you watched the Games for Change presentation last week, this should look pretty familiar (see 22:30).
There’s a lot more to explore with this concept. Expect to see more of it in the future.
Physics with Portals 