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Friction problem

  1. Sep 25, 2005 #1
    The question is:

    A car is traveling at 50 mi/h on a horizontal highway. If the coefficient of static friction between road and tires on a rainy day is 0.10, what is the minimum distance in which the car will stop?

    I know how to solve it using static friction, but I don't understand why only static friction is needed in the problem, and kinetic friction does not apply.
     
  2. jcsd
  3. Sep 25, 2005 #2
    What is static friction? A force which prevents any relative motion until its threshold is reached. So in order to keep the friction between the road and your tires, you must maintain a minimum acceleration. And once you find this acceleration, you can find the minimum distance it will take to stop.
     
  4. Sep 25, 2005 #3
    so does that mean, when I press the breaks, there is only static friction between the tires and the road?
     
  5. Sep 25, 2005 #4

    Päällikkö

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    With (an ideal) ABS, I suppose, there's only static friction(?)
     
  6. Sep 25, 2005 #5

    Integral

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    That is correct, as long as your wheels are not skidding they maintain static friction with the road. Consider the difference between skidding and rolling.
     
  7. Sep 25, 2005 #6
    ohh, ok, I get it now. Thank you for the help
     
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