Physics 11 – Today the students worked through the formula for Universal Gravitation. The students felt pretty good about how gravity works, having covered it conceptually already. However, there were still a few surprises (mostly for me).
It became apparent to me that many students consider the re-ordering of variables in a formula as something that makes a new formula. For example, after rearranging the formula to solve for r, separation, I was asked several times if the students would be given this formula on the formula sheet.
The second big surprise was being asked if the N*m^2/kg^2 units for G were variables, and what numbers should be plugged into them.
The above two misconceptions will have to be something that I specifically address again the future.
BC Physics 180 
I see my students confused about units vs. variables. I’m curious what you will try and how students progress. I’m not sure I’ve ever done much to explicitly address it.
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I would consider using Peer Instruction to attack this misconception. However, if the large majority of the class gets the idea, peer instruction doesn’t work as well for those that need help.
I think an underlying reason for why students have a problem with mixing units and variables comes down to an overall problem when working with symbols. I’ve seen similar confusions and misconceptions when teaching math. It would be interesting to try and find out the brain science behind this topic. Why are some people much more comfortable working with symbols than others?
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