Sunday, April 3, 2011

One Situation: Multiple Force Models

I like this picture. And one reason I like it is because it reminds me that there is no correct way to a model a situation using a free-body diagram. Here are four free-body diagrams.

While the models becomes more sophisticated; I don't think any of these models is correct or incorrect. Depending on its purpose, sometimes the simplest model is the best one. All of this makes me wonder what dis-service we do to students when we over-emphasize the correctness of a free-body diagram and under-emphasize the fact that we are building and refining models. As we come to notice and become concerned about more nuanced features of a situation, we may (or may not) choose to attend to those features.


  1. Brian, this is absolutely awesome! I wonder what students would actually do with (or to?) this problem, especially after we have kept hammering them with the "simple" free body diagrams in intro physics...

  2. Yeah, I think it could be interesting to see what students do, especially if you were to explicitly ask them to draw more than one free-body diagram to model the situation. They would probably need some practice, and might go better in groups, but I think it could go well if done right.