How to Work a Physics Problem in Four Easy Steps

Here’s the first class lecture from my former teaching days in a nutshell.  I’d grade on four things (hold up fingers) roughly equally, be they homework or test problems, and I’d tell the students to break the work down the same way.

1. Identify the equations from the text that seem relevant to the question.  What we were just talking about in class should give a big hint.
2. Start setting up the problem.  Identify what in the equations from Step 1 are given, what is being asked for, what the missing pieces may be.  Maybe sketch out the physical situation, but at least set up a coordinate system.  Go get more or different equations if there are loose ends, spare pieces, or missing parts.  Underlining the symbols in the equations for given information in green, the target unknown in red, and stuff to be gotten from other equations in blue can really help with this step.
3. Do the math.  Not with a calculator, solve for the answer analytically, pencil-and-paper style, keeping everything in symbols.  You want to end up with the variable you’re solving for neatly isolated so that you can plug in numbers and have an answer pop out.
4. Plug in the numbers and check your answer.  Is the value reasonable?  Or are you predicting that it will take 3600 seconds for a coyote to to fall off a 20 meter high cliff?  Take a moment to explain your cross-checking on the answer.

1-2-3-4, easy for the students to lay out, easy for me to grade.  I’d give an example here, but I’m too tired to sort out math symbols on blogspot right now.  “Left as an exercise for the student” as the saying goes.  Naturally, this is 1-2-3-4 is only a beginner’s technique.  Too frequently in the course of research, just coming up with the equations for Step 1 is the real problem.