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A great check of BFPM understanding

November 2, 2010

Inspired by a similar question Kelly O’Shea created for a test, I decided to write the following mini-asessment for my students.

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This is an awesome assessment of whether students really understand Newton’s 1st and 3rd laws, or whether they hide behind formulas and memorized rules to get answers. In this quiz, there’s really no place to hide, and it showed that my students have some real weaknesses (as I’ve blogged about before, when it comes to distinguishing whether a par of forces are equal because of N3 or N1). At the same time, many of my students did a masterful job of explaining, step by step, why the reading on the scale changes, which shows that they really are learning to use physics to break apart complex situations into smaller interactions between objects.

Since I’m out on paternity leave, I couldn’t go over this quiz in detail with my kids, so I typed up the following explanation. Note: Keynote for mac really is one of the quickest and easiest ways to make accurate FBDs, since it automatically measures angles and lengths of arrows as you draw them.

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Also, in case you are interested, here’s one set of sample student responses for you to see what my student work looks like on this assessment. One of the things I’m also trying to do (thought it isn’t so obvious in this set of assessments) is offer praise and suggestions on how to build habits that allow you to tackle more difficult problems (clearly labeling forces, explaining your reasoning, making diagrams large enough to be useful). I find being positive in giving written feedback to be one of my biggest challenges.

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