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Standards Based Grading, Week 4

February 11, 2013

Day 11 (Monday):

The take-home message today?

Intensity level is a scaled value for sound while sound intensity is more of a raw value for sound (dependant on its frequency and amplitude).  And, while intensity can be calculated from physical properties of the source, most references to “intensity” in everyday usage are really referencing “intensity level.”

We worked a problem as an example going back and forth between the two (intensity and intensity level).  [If one child is “loud” at 75dB, how loud would a room full of 30 children be?]  This activated a standard.  So all in all, a productive day.   This does lead to a question to others doing SBG:  what is the average rate of activating standards?  One or two per week?  One or more a day?

Day 12 (Wednesday):

We discussed Doppler effect today.  For a break in pace, we first discussed how Doppler radar works in an important everyday example (everyone in OK knows about Doppler radar–access to weather data and imaging in this state is phenomenal).  Increasing/decreasing distances between reflected wavefronts off of a distance cloud is a concept students grasp well, so I went with it.  Then the equation(s) were put up on the board for determining the observed frequency.  I like combining the expressions with a +/- in the numerator and a -/+ in the denominator.  General rule: choose the upper sign for approaching and the lower sign if motion tends away from the other.  We worked a couple of examples, then I gave a more challenging/conceptual question:

If you are swinging a buzzer at the end of a string in a circle with a constant angular velocity, what would the observed shifte frequency as a function of time plot look like?

To force students to consider a scale on the plot, I gave values for the angular velocity, radius of the circle and the frequency of the source.  A curious feature of this problem is an unexpected hangup students had (and I should have anticipated it): confusing the angular frequency \omega = 2 \pi f of the swinging sound source with the frequency f of the sound coming from the source.

Anyway, long story short: after all was said and done, all of the standards were active at the end of class.  I’m getting excited about moving on to new material–now I just have to polish up the new standards!

Day 13 (Friday):

Pop quiz again!  This time we looked at a video: http://www.youtube.com/watch?v=_d8ROhH3_vs .  The question was,

For which segments of the film loop are depictions of the Doppler effect accurate and innacurate?

I’d intended this to be a real quiz, but we ended up talking about it as a group discussion.  It turns out students could answer it pretty easily, but even they recognized that they’d never really questioned sound effects like this before.

We then began electrostatics, using some PhET simulations as an introduction.  It’s amazing how much content can be pulled from the balloon and John Travoltage sims!

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3 Comments
  1. Andy "SuperFly" Rundquist permalink

    I tend to shy away from doppler radar examples when I’m doing sound doppler, just because the formula for light is so different from sound (the extra square root). Is that an issue for you?

    As for how many standards per day, I’ve found I really like having exactly one per new content day. It focuses the day very well for me.

  2. Andy "SuperFly" Rundquist permalink

    just a place holder so I get email notifications (sorry, forgot to check the box on my last comment). Move along, nothing to see here 😉

  3. And here I was excited to get two comments within an hour of publishing a post 🙂

    I’m afraid I am guilty of doing some handwaving with the Doppler radar example. I drew out wave fronts and we arrived (conceptually) at how distances between reflected fronts vary. Then we moved on to sound and worked out the corresponding equations without looking back. You’re right though, the functions are not the same. Same basic principle, different quantitative relationships. I’ll have to see if students picked up on the discrepancy . . .

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