Physics Stack Exchange is a question and answer site for active researchers, academics and students of physics. Join them; it only takes a minute:

Sign up
Here's how it works:
  1. Anybody can ask a question
  2. Anybody can answer
  3. The best answers are voted up and rise to the top

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

share|cite|improve this question
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.

share|cite|improve this answer
Thanks for the insight – Nils_e Feb 28 '13 at 8:29

Your Answer


By posting your answer, you agree to the privacy policy and terms of service.

Not the answer you're looking for? Browse other questions tagged or ask your own question.