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orangeblue

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- I teach an introductory physics course. It's the first time the students have ever seen physics and they struggle a LOT at first. We start with Kinematics. To try and simplify things, I ALWAYS call up the positive direction, down negative, right positive, and left negative. The idea is to get them used to assigning a sign to direction. It usually works out fine - students mostly get it.
- In Dynamics, I start to have problems. Here's what I do:
- I define Fnet as the SUM of the forces
- For solving math problems, I've found that using Fnet = (bigger force) - (smaller force) works best for most scenarios. However I run into problems trying to explain why the subtraction sign is there when Fnet is a SUM.
- I tried to tell the students we're making the direction of the bigger force the positive direction, but they just got super confused and I had a hard time explaining it.