I haven’t posted in a few days, so this is going to be a long one, covering three whole days of exciting BFPM work!

After finishing our main balanced forces practice sheet, I introduced the “sum of forces equation” notation. My hope is that students will work the kinks out of using it during the BFPM unit, and then the UFPM unit will be a cinch.

At the end of Tuesday’s class, we looked at a really simple example from the PhET Force Basics simulation (http://bit.ly/phetforce), involving three people in a tug of war. We’re given Fmedium on cart and F large on cart, but we don’t know Fsmall on cart. Finding the value is easy peasy for students, but it’s an opportunity to practice this new approach. The takeaways here are a) this equation is handy for finding values we don’t know, and b) we NEED to set a positive direction before the positive and negative signs have any meaning.

Then, we spend a day working on a practice sheet based around five lab stations, two of which are shown here. There’s also a falling coffee filters problem, a problem with an object supported from above and below, and a problem involving a collision between a bowling ball and bowling pin. For each, student have real stuff to play with and observe. They can use force meters to, for example, figure out that the water has to be pushing upwards on a block when it’s submerged, or make careful observations to see that the interaction that speeds up the bowling pin slows down the ball.

The two scales pushing upward plus the Earth pulling downward sum to 0N, as long as you’re not bouncing around.

The force exerted by the water on the cork balances the force exerted by the Earth exactly, but isn’t great enough to balance the force exerted by the Earth on the brass object.

Then, on the following day, we whiteboard the examples (with mistakes!), to get a solid idea of how to use this stuff. It goes a little quickly, and I wonder if it’d be better to spend even more time on the whiteboarding here, but it’s unquestionably awesome.

Students have the stuff with them when they’re presenting, so they can use it to illustrate their points. Simply having things to use as visual aids can contribute significantly to engagement while whiteboarding, especially if some of the audience didn’t get to play with that stuff.

##bfpm ##physicsfirst ##whiteboarding ##representations