when does friction in a car becomes positive? in a dry surface and i na wet surface and on ice.
You should know why this question doesn't make sense. What you call "positive" and "negative" are really arbitrary. It is in reference to the coordinate axis that YOU (or anyone else) set up. If the frictional force happens to be in the same direction as what you call "positive x-axis", for example, then it is positive!
Maybe, indirectly, the proper setting up of coordinate axis could be the source of your problem. I would recommend looking at one of the tutorials that we have on here to see if this is something you should understand first.
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