Physics: Preconceptions in Mechanics – Gravity

I’m attempting to use Preconceptions in Mechanics again this year. I started it last year but never finished the sequence.

I’m also using Frank Noschese’s sequence of Gravity, Normal, Friction, Tension, then Inertia. He has written a lot about the why’s and how’s of his sequence. I see its merits but also feel the suggested sequence the book has works equally well (starts with normal force).

Preconceptions in Mechanics (hereafter, PiM) relies heavily on demonstrations, class votes, and discourse to drive the lessons. The first vote is always the target scenario we want the students to understand and is, also, the most frequently misunderstood scenario. The book is then built in such a way to have students vote on more and more predictable scenarios and culminates back at the target (hopefully with better results)

NOTE: I am using Plickers to do the voting and am loving the results. It takes a bit longer but is better than the PollEverywhere method I used last year. If you do any type of in-class voting, I highly recommend Plickers, especially if your students do not have devices.

The first lesson in the unit in gravity deals with the causes of gravity. Before the break we learned how to calculate weight, but never where weight comes from. It analyzes four different scenarios: gravity is caused by earth’s magnetic field, gravity is caused by earth’s rotation, gravity is caused by earth’s atmosphere, and gravity is caused by earth’s mass.

The first time I read the book I almost laughed off the idea that my students would think gravity was caused by any of the first three factors, but after issuing the recommended pre-survey I found that each of the beliefs were not only represented but were more prevalent than the idea that mass causes gravity.

I followed the book pretty much to the letter with the exception of handing students a copy of planetary data and asking them to analyze it for each factor (Frank’s idea).

Since we are on 90-minute block schedule I was also able to start on Gravity 2 in the book which focuses on the idea of masslets and the equality of the gravitational interaction.

This lesson didn’t have a ton of excitement from students (Gravity 2 was better than Gravity 1). Since then I have done several others from the book (posts coming soon) and this one was by far my least favorite, the rest are actually quite enjoyable.


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