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Realistic answers and the state of physics resources on the internet

March 24, 2011
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Today, I was being a bit lazy when making up a quiz, and I decided to google “momentum problems.” Big mistake. Check out the top hit.

It’s a randomized page of simple problems, so you won’t get the same results I did, but Here’s a sample:

A small car (mass = 133 kilograms), moving at 98 m/s, crashes head on with a 532 kilogram truck moving at -63 m/s in the opposite direction. If the two cars become ?intertwined and mangled (inelastic), with what velocity does the wreckage move? (Don’t forget direction!)

Are you serious? What small car has a mass of 113kg and can move at 98 m/s (219 mi/hr)?

This gets me thinking two thoughts:

  1. How are we teaching students to check their answers for reasonability? Is this part of getting them to see the significance of their work? I love open ended problems, but I think I need to work more on getting my students to think about the significance of their findings, and question the reasonability of their results.
  2. Why are most of the resources that google returns for physics teaching searches so bad? It took me years of searching physics teaching blogs and finding a bunch of useless stuff before I ever stumbled upon Frank Noschese’s blog. Why is this? Are people linking to crappy problems that involve clown cars traveling at Ferrari speeds? Why would this be? And more importantly, what can be done about it?
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13 Comments leave one →
  1. March 24, 2011 11:26 pm

    So let’s get started on the physics assessment database!

  2. March 24, 2011 11:28 pm

    This made me laugh out loud — much needed while lesson planning at midnight. What a great visual (does it really say intertwined and mangled?). Pseudocontextual physics problems are a hilarious graphic novel waiting to happen.

    Getting students to check their answers for reasonableness (reasonability?) aside, what about having students critique physics texts for reasonableness? Self-assessment is tough, and checking your answers means confronting the idea that you might be wrong, and might result in you having to do your work all over again. All of those things are motivating me to “forget” to check my answer. But criticizing others… especially an authority or a teacher… that could be fun. How about a worksheet cherry-picked through Dan M.’s PS series?

    I think of this only because yesterday my students took great relish in pointing out an egregious mistake that I had immortalized in a screencast. They got so much out of it (showing me the correct calculation, proving 18 ways that that result could never physically happen) that I’m considering a new series: find the teacher’s mistake. Screencasts in class are a perfect medium for this, because they go by quickly enough that you have to estimate or “reason through” (not enough time to be keeping up with a calculator). Plus, the “reveal” is going back through the video, pausing at each spot where students suspect the mistake might be hiding.

    • March 24, 2011 11:34 pm

      Mylele, I LOVE this idea. It also reminds me of the work that Derek is doing to create videos that expose student’s misconceptions through discussion. This might be a way to make video learning far more interactive. I could imagine tons of possible scenarios where I solve problems incorrectly, and students have to find and correct the mistake. Thanks for inspiring me with a great idea. Now I just need to find the time to start doing these screencasts.

      • March 24, 2011 11:43 pm

        All of a sudden, those awful problems are magically turned into a valuable treasure trove. A lot like compost, now that I think of it. Plus, you can recycle them again: next day, give the same problems, but the task is, fix this. So organic, it should count toward your school’s waste diversion program.

  3. March 25, 2011 6:56 am

    Yeah, it is funny we both posted about a very similar theme. http://tinyurl.com/6zbya2c

    I am definitely troubled by #2. Why google can’t find good physics teaching and learning? What can we do about it?

    I got here because of a phone call from a friend, who mentioned Dan Meyer’s TED Talk. I checked out his blog, which led me to Frank’s blog. I left a comment on Frank’s blog, and Frank emailed me, and invited me to join twitter. And then explosion.

    My point is this. I got here because of the “excitement of a friend” who wanted to share something, then “a little bit of curiosity” and digging around on my part, but only really because of the “kindness of a stranger” to welcome me in. When I say it that way–excitement, sharing, curiosity, and kindness–it doesn’t sound so bad. But excitement, curiosity, and kindness aren’t what make google run.

  4. March 25, 2011 5:13 pm

    John: How are we teaching students to check their answers for reasonability?

    How reasonable is it of us to expect students to check their answers for plausibility when the representation of the problem is static, printed, and, really, lacking any visual representation at all? The problem here describes a car crash — an event in motion — and yet we’ve abstracted and decontextualized it past the point of recognition or intuition. Then we lament that students fail to check their answers on what they recognize or intuit to be true. We’re asking for more than we can reasonably expect here.

    • March 25, 2011 8:58 pm

      I totally agree. Bear in mind this isn’t my problem, it’s what I found lazily googling problems. It would be far better to show the students a video of a crash, and have them analyze it in tracker video analysis. But, if we are going to ask students to do boring textbook problems (with gee whiz randomized numbers) I think we have to ask that the numbers used in the problem meet a standard of reasonableness. Anti-context vs pesudo-context, perhaps.

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  1. Proof of concept: could students learn more if Kahn made mistakes? « Quantum Progress

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