Snow wave

Earlier today I posted this pic and asked a question about it on twitter:20171210_102417

If you click through you’ll see lots of great ideas. I’m not sure what the right answer is, so feel free to weigh in below in the comments.

What actually made me decide to blog about it was that I realized that I asked the wrong question. I really wanted to know what would cause the repetitive pattern, so I think really I was thinking about what would cause the frequency of the wave.

Now, I think everyone who replied on twitter recognized one of the fundamental relationships about waves when answering my question:


and really just jumped to physical descriptions of what might cause that frequency. In other words, they realized that the car was moving and basically leaving behind a trail of snow blasts at a particular frequency. Spatially that all works together to leave a record with a measurable wavelength.

As I thought about both my question and the answers throughout the day, it hit me that it’s one of those things that might lose students, especially early on before they’ve really internalized the relationship above. If you ask students to engage with the image or even the Hyundai commercial it comes from, they’ll engage and come up with all kinds of interesting questions, it seems to me. But if you ask about the wavelength like I did, it might shut them down, because then they’re not going with their gut and instead are trying to remember the relationship between wavelength and frequency (or possibly period).

I guess what I’m saying is that I knew my audience and I figured I could ask the question any way I wanted to. And it worked! But as I think about using this in class, I think I would have to be more careful. I think that’s a cautionary tale for me. It reminds me of times I’ll ask about something I think they’ll have experience with, or maybe some cool insights about, but I’ll ask it using vocabulary that’s still too new for them. I think instead I should just show them something and ask “what do you see?” or “what do you think is going on here?” or “Is there anything interesting going on?”

Your thoughts? Here are some starters for you:

  • This is interesting. It reminds me of . . .
  • This is really dumb. What you should have asked instead was . . .
  • This is really cool. I think I’m going to buy a Hyundai now.
  • This is really a waste of my time. I already have a car.
  • Why didn’t you post a link to the video instead of a crappy screen grab you clearly took while pausing the tv during a really exciting Manchester Derby?
  • Here’s a better question to ask students about this pic . . .
  • I was the driver in this commercial and here’s what actually caused that . . .
  • I was the camera person in this commercial and here’s why the driver really doesn’t understand physics.
  • Here’s my crazy explanation for that snow pattern.
  • It’s not a wave, you should stop saying that.



About Andy Rundquist

Professor of physics at Hamline University in St. Paul, MN
This entry was posted in physics, teaching, Uncategorized. Bookmark the permalink.

7 Responses to Snow wave

  1. Charlie Payne says:

    Andy – isn’t this related to the position of the snow on the wheel? Assuming tangential dispersion, wouldn’t the rearward “spray” depend on the angle through which the wheel turns, limited by the uppermost position that produces a vertical or near-vertical spray, and the wheel well?

  2. Charlie Payne says:

    Ah, silly response from me. I’m wondering if there is a critical amount of snow that sticks to the wheels, peeling away as some critical mass is reached…I’m really interested in this as a teacher…

    • Andy "SuperFly" Rundquist says:

      I would think the critical mass approach wouldn’t be so regular (I guess I’m leaning toward Peter Bohacek’s idea of traction control)

  3. mt says:

    Hmm, maybe the aesthetic of the person who photoshopped the image? Let’s start with whether this is a real phenomenon.

    • Andy "SuperFly" Rundquist says:

      It’s possible, but it certainly wasn’t me 🙂

      It’s such a quick part of the original commercial that I don’t think it would be worth their time to do any doctoring. Who knows, though.

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