What is negative velocity and negative direction of the velocity?
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2$\begingroup$ If you rotate the coordinate direction along a positive velocity by $\pi$ radians you have in this new coordinate system a negative velocity. What is a positive and a negative velocity depends on one's choice of coordinates. $\endgroup$– Lawrence B. CrowellCommented May 29, 2016 at 13:40
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1 Answer
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It's just a mathematical artifact. If you define north as "plus in the x direction" then a car driving south will have a negative velocity. You could equally well define south as "plus in the x direction" and then a car driving north will have negative velocity. Or you can define velocity from the car's point of view, in which case driving forwards is positive velocity and driving in reverse is negative. It's purely down to how you set up your mathematical model of reality, it has no special bearing on reality - for example, no matter what happens, your car isn't going to make fuel just because it has "negative velocity".
