Airplanes, cars, sticks and stones: Brian Beckman on the physics of simulation

My wish for Channel 9 to augment the trademark videos with downloadable audio files has been granted. As a result, I was able to listen to Charles Torre’s interview with Brian Beckman during my exercise hour yesterday. Even if you’re not a gamer (I’m not), there’s a good chance you’ll enjoy Brian’s lively explanation of the physics that govern the simulation of planes and cars. I guess I’d been vaguely aware that PC flight simulators predated PC racecar simulators by many years, but I’d never thought about why.

To do a credible simulation of a plane, Brian says, you only need to account for two coordinate systems (the earth’s and the plane’s) and four forces (lift, drag, thrust, gravity). Because you can do table look-up for the values of variables such as lift and drag, and because those tables are small, you don’t need a “fast and fat” computer (fast CPU, big memory) to do the job. That’s why Flight Simulator was possible on the earliest PCs.

Since only some of us fly, but most of us drive, you might have expected automotive simulators to have arrived sooner than the mid-1990s. And they would have, were it not the case that car physics is, counter-intuitively, way more complicated than airplane physics:

If you analogize a tire to a wing — that is, the thing that generates the force — you’ve got four of them. And they’re connected to the car by these complicated linkages. Maybe they’re McPherson struts, maybe they’re independent suspensions, maybe they’re leaf springs. All of these things act differently, so each different car is going to have not just different shades of physics, but completely different kinds of physics, completely different equations.

It goes on from there: more coordinate frames to account for, complex dynamics of steering, acceleration, and braking. It’s fascinating to learn why accurate simulation of cars only recently became possible on PCs. Along the way, you’ll be reminded about the properties of the safety envelope that ordinary drivers seldom push but that race drivers always do.

The interview concludes with another counter-intuitive observation. Although the ability to crunch complex nonlinear equations at 30 or 60 frames per second is what makes these simulations possible today, Brian thinks this radically different approach is the way of the future. The Rigs and Rods system shown in that video, created by Pierre-Michel Ricordel, uses a technique that Brian calls “sticks and stones”:

Stones, which have mass, and sticks between them which are little flexible things we can model with very simple physics: harmonic oscillators. That’s all you need, just one physics model, a damped harmonic oscillator connecting pairs of stones, and, by gum, you can simulate really amazing things.

The computer is now fast enough to be able to simulate hundreds or thousands of these independent systems simultaneously, every step. We can now dispense with the really hard mathematics. If you’d asked me to bet money that this were even possible, I’d have said no. But that’s because I had this long experience where you just didn’t think about doing thousands of particles iterated in a system like this. Here’s a guy who took a fresh approach, he said let me see what I can do, and sure enough, this is a magnificent system.

We’ve heard it before, we’ll hear it again: a network of many simple parts trumps one big complex monolith. It’s a story that keeps on surprising us, but probably shouldn’t.

So, you might wonder how a video with as much visual content as this one — equation-filled slides, Mathematica screens, YouTube videos — fares in audio format. In this case, surprisingly well. It’s amazing how much information voice alone can carry. Later I did review parts of the video, and having listened I knew just which parts I wanted to see. But this exercise confirmed my belief that downshifting from video to audio is a really useful way to give people access to long-form material they might not have time to watch.

5 Comments

  1. It isn’t just that the downshifting from video to audio gives access to material one might not have time to watch, but as radio Mathematics instructions in Nicaragua provide, it is likely more “successful” because there is no distracting video — when only one sense has to supply the info to the brain, the “richness” doesn’t overcome the message.

  2. “when only one sense has to supply the info to the brain, the “richness” doesn’t overcome the message.”

    I understand what you mean, and in general I agree.

    In this case, the video does add value in two ways. First, it’s full of equations and charts that Brian refers to. It’s not necessary to see those in order to follow the presentation, but it’s helpful. Of course they do boil down to a set of slides (plus some video clips) that you could review before or (as I did) after listening.

    Second, there’s emotional bandwidth. If you were to simply read a transcript of what Brian said, you could get through it quicker than by listening. But voice adds a lot of emotional content. It conveys who Brian is, and how and why he is passionate about the topic, and that counts for a lot. In the same way, video adds even more of this emotional content. That said, once you sample 10 seconds of video, you’ve absorbed the essence of how he looks and acts. Now you can project that onto the voice.

    “radio Mathematics instructions in Nicaragua”

    I looked that up and it sounds interesting. Wouldn’t you say, though, that if they could have done what Tim Fahlberg does with his mathcasts (http://weblog.infoworld.com/udell/2006/09/29.html) back in the 1970s, they would have preferred to? In this case, you really do want to watch the equations being solved while you hear a narrative about the process.

  3. Of the video podcasts I listen to the audio of – only a few, like a recent TVO BigIdeas talk on Quantum Cryptography – have driven me to want to watch the video. Usually I find audio is more than enough. I think there’s something to be said for not relying heavily on visuals in talks for that reason. I do miss laughing at funny slides I hear crowds chuckle to in audio podcasts occasionally though.

    Saying that, I do think about what I may be missing in the learning process when just listening to audio. Missing in that additional symbol auto-association probably happens in my head when I’m watching something like Dr Quantum or getting the essence of someone like you mention. Video potentially associating more than just words and sounds together with my existing knowledge in ways that help me remember it. I tend to think of it as firing multiple sensory stimuli together, and having it wire together forming stronger memory associations. I think it really depends on the context in which your learning though. I find it’s easier to switch off visually than it is audibly. I do know audibly; research has shown faint indistinguishable background noises are more distracting than obvious noises. Earbuds tend to block a lot of that out and help me concentrate. Earphones tended to let in noise and distract me more. On the other hand audio with video has the advantage that if you miss one, the other may fill-in the gap.

    GrammarGirl, another of the podcasts I listen to occasionally includes a mneumonic to help listeners learn grammar tips. Occasionally she’ll include a cartoon on site to help listeners remember. Having a picture to associate with the process helps immensely. Someday I just hope she remembers my suggestion to add the cartoons as the podcast cover art. But then I may never visit her website and the other offers on display there…

  4. “I do miss laughing at funny slides I hear crowds chuckle to in audio podcasts occasionally though.”

    Yep. I’ve never heard this done, but it would be cool if in post-production an editor’s voice would interrupt briefly and say: “For those listening, it’s a picture of a pony” … or whatever. Wouldn’t that be a nice touch?

  5. And for normal desktop PC stuff, your 3GHz (or whatever, I don’t even know what the current high number is) CPU is idle most of the time, with the bottlenecks being I/O.

    So when am I going to have a hundred simple 400 Mhz processors on a super fast bus all churning away in parallel, rather than a big complicated CPU spitting out heat and not really doing anything?

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