Sometimes the same procedure shows up in two different contexts. This is especially common in the fields of math and science, as science employs in real-world application many of the techniques we learn in their abstract form in math class. For some reason, the principle as shown in a high-school science class is often much harder for students to understand than it was in the math class. (My personal theory is that science teachers are applying the concept in a way that changes how they explain how it works, and they probably have not collaborated with the student's math teacher to ensure they're reinforcing the same terminology.) Last week one of my students ran into this phenomenon in her own work; a concept from last year's math class showed up in her physics class. To help her understand it, we went back to the original math concept and talked about proportions. The science homework she was struggling with was the old chestnut about unit conversions; rows and rows of fractions... read more