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I'm working on a sample problem and it asks on how steep of an incline can a car park? From what I learned the friction is in the opposite direction if there was motion in said friction-less environment. Is this the right way to think of friction?

In the case of the car; it would move down the hill and the friction would be up the hill. Why is the friction pointing down the incline and not up the incline?

enter image description here

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up vote 3 down vote accepted

You're right that friction points up the hill. What happens when you solve this is that you get a friction force that's negative. A negative force pointing down the hill is the same as a positive force pointing up the hill, so everything works out okay. It would have been more clear if the diagram author showed the friction vector pointing uphill to begin with, though.

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Thanks for the insight –  Nils R Feb 28 '13 at 8:29
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