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vector directions



I am having trouble getting my "regular" (i.e. non "gifted and talented") physics students to understand how to determine the direction of a vector. We have defined direction as the angle measured counter-clockwise from the +x-axis to the vector. Specifically, they have trouble when one or both (we are working in 2D) of the components of the vector are negative in which case simply taking arctan (y/x) does not yield the proper angle.

I have shown them how to construct a triangle from the vector components and the vector and then to use the angle to find the direction (i.e. add to 180 degrees or subtract from 360 etc). Does anyone have success with something different?

Thanks

Justin Parke
Oakland Mills High School
Columbia, MD