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B Force and friction

  1. May 21, 2016 #1
    We know that force * coeff. of friction = m * g. . It does not make sense. Pls read details. This is when force is applied perpendicular to the direction of friction. But suppose we say that m = 10 kg, g = 10 m/s2, coeff. of friction is 0.1. Then by formula it says that force required to keep the object against the wall will be 1000 N. How does this make sense? I mean the force required to lift the object without any support is just m*g = 100 N. Pls explain this so that it makes intuitive sense......
     
  2. jcsd
  3. May 21, 2016 #2

    Simon Bridge

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    Of course it doesn't, it is nonsense.

    This is not correct ... the usual equation is ##F=\mu N## where "N" is the magnitude of the contact force between the surfaces.
    Where that is a horizontal flat surface, ##N=mg## ... which is to say it's the weight of the object.

    Oh you mean that you are applying the normal force?

    If you want friction to hold a box against it's weight, on a wall that slippery, then sure ... you will need a lot of force... especially if you are only applying the force horizontally.

    Please see:
    http://hyperphysics.phy-astr.gsu.edu/hbase/frict.html
    http://www.engineeringtoolbox.com/friction-coefficients-d_778.html
     
    Last edited: May 21, 2016
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