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Calculating frictional force given mass and coefficient?

  1. Jul 9, 2015 #1
    The mass of a steel block is 760.9 g, the static coefficient of friction is 0.15, how do i find the frictional force in newtons?
     
  2. jcsd
  3. Jul 9, 2015 #2

    anorlunda

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    The area of the block in contact with the surface needs to come into the picture.
     
  4. Jul 9, 2015 #3

    A.T.

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    You can't, from this information.
    How would that help?
     
  5. Jul 9, 2015 #4
    0.00032258 meters^2

     
  6. Jul 9, 2015 #5

    anorlunda

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    OK, and the unite of the coefficient 0.15 are what?
     
  7. Jul 9, 2015 #6
    I thought Coeff of friction was the ratio of Frictional force to force pushing the bodies together, it is scalar, right?
     
  8. Jul 9, 2015 #7

    anorlunda

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    I beg your pardon, you are correct.
     
  9. Jul 9, 2015 #8
    So multiply 0.15 by mass in kg?
     
  10. Jul 9, 2015 #9

    jbriggs444

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    The kilogram is not a unit of force. It is a unit of mass. Given an objects mass and the local acceleration of gravity, you can determine how much force is required to support it, however.
     
  11. Jul 9, 2015 #10
    Ok, I got 7.45 for the force required to support it, and 0.15 x 7.45 is 1.118 Newtons. Look good?
     
  12. Jul 9, 2015 #11

    jbriggs444

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    Yes. 0.15 times 7.45 Newtons is 1.118 Newtons.
     
  13. Jul 10, 2015 #12

    A.T.

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    Note that this is not the actual static friction, just the maximal value it can reach given a normal force of 7.45N.
     
  14. Jul 11, 2015 #13
    Usually, F=mu*Wt frictional force equals some constant (coefficient of friction) times normal (perpendicular) force. Although there are differences between sliding friction and static friction, their correlation is close to 1. That doesn't mean they are equal.
     
  15. Jul 11, 2015 #14
    Sliding friction can often be approximated by F=mu*N. You know mu, you know N (normal force). Sliding friction is almost constant for slow sliding (<<<<<<<<<<c).
     
  16. Jul 13, 2015 #15
    max static friction calculated as 1.118 newtons is correct provided there is no vertical acceleration of the surface, and it is perfectly horizontal.
     
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