## Day 96 – Universal Gravitation Physics 11 – And then there was the dreaded Universal Gravitation….  Why dreaded?  Despite my best efforts, students have a lot difficulties manipulating this equation. So many variables, so few numbers.  I generally find that students have a pretty fuzzy idea of algebraic manipulation.  They know some rules to follow (“if you have 4x, divide both sides by 4 to get rid of the 4”), but are pretty unclear on the mathematical underpinnings.  I looked at my son’s Math 9 textbook and I could see why this is the case.  I *think* that it would help to develop some understandings like: “the variable term will have a coefficient in front of it. Use the associative property to separate the coefficient and the variable, then multiple the term by the reciprocal of the coefficient so that the coefficient is 1.”

Other people may see the above as being too prescriptive or wordy, or not easily understood by students.  However, if a few of these steps are deliberately practiced, I would hope that the methodology would become clear and make sense.

## Day 74: Universal Gravitation 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.