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Static friction at its maximum in relation to the magnitude of the applied force?

  1. Jan 9, 2012 #1
    1. The problem statement, all variables and given/known data

    Which of the following statements are true about Fs, max in the equation mu=Fs, max/Fnormal?

    I. Fs, max is exerted perpendicular to the surfaces in contact.
    II. Fs, max represents the maximum value of the force of static friction.
    III. On a level surface, the magnitude of the Fs, max equals the magnitude of the applied force that starts the object moving.

    2. Relevant equations

    mu=Fs, max/Fnormal?

    3. The attempt at a solution

    Well, I know that Friction is parallel to the surface and opposite to the direction of the force on the object, so I is out of the picture, and II seems a bit obvious, so that's one true answer. I'm not understanding the third one, though. Help? I just need an explanation to III to know if it is true or false.
  2. jcsd
  3. Jan 9, 2012 #2
    The maximum static friction will be at the instant just before the object starts to move. For example, if
    [tex]F_{S, max}=12.000000000[/tex], then I would assume [tex]F=12.000000001[/tex] would be suffice to induce movement, which is essentially 12.
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