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Homework Help: Finding friction coefficient, car unbanked curve.

  1. Oct 15, 2015 #1
    1. The problem statement, all variables and given/known data
    What is the minimum coefficient of friction needed between the tires and the ground so you make the turn safely?

    Car= 1394.7kg
    Radius of turn = 40m
    Velocity = 20m/s

    2. Relevant equations
    Fnet = MAc (Ac = centripetal Acceleration) = Force of friction
    Force of Friction (Ff) = Mu(Fn) of Mu(mg)
    MAc = (MV^2)/r

    3. The attempt at a solution
    (MV^2)/r = Mu(Mg) mass cancels out and i solve for mu ==> mu = (V^2/rg)

    mu = 20^2 / (40*9.8)= 1.02

    If that is correct is it possible for the friction coefficient to be more than 1?
  2. jcsd
  3. Oct 15, 2015 #2


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    Homework Helper

    Yes, it can be between the tyre and the asphalt.
  4. Oct 15, 2015 #3
    So since the Friction coefficient is more than 1... that just means it is stronger than the normal force? but is that the minimum?
  5. Oct 15, 2015 #4


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    Homework Helper

    What is minimum? The maximum of the static friction is μmg. Now μ is slightly greater than one. Imagine the tyre is sticky, you put some glue on it. In that case the "force of friction", the contact force between the tyre and asphalt can be quite big.You can find μ-s greater than 1 in this table. http://www.engineeringtoolbox.com/friction-coefficients-d_778.html
    μ>1 means that you need greater force to pull the body on the horizontal force than to lift it vertically.
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