Day 132: Equilibrium Forces

Wednesday, 19 March 2014


An example of a basic equilibrium problem from my class.

Between questions on homework and classwork, we’ve slowed down on the friction lab so that we might dive back into equilibrium. Kids have a quiz on equilibrium Thursday or Friday this week.

So, when I teach about net force and equilibriants, I take a common-sense approach rather than teaching kids the “steps” to solve. First thing I have them do is draw a picture and identify the quadrant their result will appear in. For instance, if two forces pull on a crate, one toward 90° and the other toward 180° and I ask for the direction of the equilibriant force, kids should realize it’ll be in the 4th quadrant (therefore the answer is between 270° and 360°).

Here’s a student solution that’s typical of the kids getting these problems wrong:


While some kids understand the intuitive part of these problems others want to memorize some algorithm. I’m refusing to give it to them which is frustrating all of us to no end. I’m beginning to feel like I need to give some incentive for a good diagram to force the algorithm-memorizers into using good habits.

I almost forgot! Wednesday was also the opening of the STEAM art show on campus. Here, a Lower School reporter interviews two of my robotics kids about their entry into the show (the robot behind them).



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