Comments on: Scheming with Schema… /blog_archive/2011/10/20/scheming-with-schema/ iteration, making, building, and coding in education Thu, 20 Oct 2011 10:44:51 +0000 hourly 1 https://wordpress.org/?v=5.7.6 By: Kelly O'Shea /blog_archive/2011/10/20/scheming-with-schema/#comment-21 Thu, 20 Oct 2011 10:44:51 +0000 http://evanweinberg.com/?p=118#comment-21 In reply to Evan Weinberg.

Yeah, the same issues come up for my students. They usually try to imagine what kind of force it must be. It is usually a tension force, so the object usually ends up being a rope. 🙂 But now you’re seeing the power of thinking with models! 🙂

]]> By: Evan Weinberg /blog_archive/2011/10/20/scheming-with-schema/#comment-20 Thu, 20 Oct 2011 10:34:28 +0000 http://evanweinberg.com/?p=118#comment-20 In reply to Kelly O’Shea.

Hi Kelly,

I completely agree – all the more reason why these random forces that ‘appear’ on problems from textbooks (and from my own old problem sets, unfortunately) don’t make sense. To really jive with the real idea that forces are interactions between objects, there must be another object involved when these forces appear. I’m not saying it won’t ever happen again on problems. I am just really energized by the fact that the students called me out on this inconsistency on Day 2 while it wasn’t even a discussion in my previous classes.

]]> By: Kelly O'Shea /blog_archive/2011/10/20/scheming-with-schema/#comment-19 Thu, 20 Oct 2011 10:27:09 +0000 http://evanweinberg.com/?p=118#comment-19 I don’t like the idea of a “source” for a force. It makes it sound like something can “have” force and then give it to something else. But really a force is an interaction between two objects. And the interaction isn’t singularly directional. Both objects experience the interaction (a 3rd law force pair being a single line on the system schema is particularly powerful when you get to that point… I do it at the end of balanced forces when they are already pros at making system schemas and FBDs).

These diagrams are also super useful when you do conservation laws. Just draw the dashed line around the entire system and easily see internal interactions vs external interactions.

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