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Homework Help: Finding the Coefficient of Friction using Torque, and Forces

  1. Nov 17, 2013 #1

    A 4.0 m long bar is suppotred by a string as shown in Figure 10-61. What must be the coefficient of friction between the bar and the floor if the bar is on the verge of slipping

    Image: 3ebcd17e8b532329dde12bc2534a4a32.png


    τ = r*F*sinθ or τ = r*F, where the force is perpendicular to the radius. Summation of forces; assuming that it, and the summation of torque is equal to 0 (static equilibrium).


    I attempted the problem by figuring out that the component of the Force of Gravity perpendicular to the bar, was needed for torque, as well as the component of Tension in the string, again, perpendicular to the bar. I am having trouble finding that component of Tension.

    I also used summation of forces and figured out that in the y-direction, we had a normal force at the pivot point, the force of gravity acting on the centre of the bar, and the y-component of the tension force.

    Essentially, I found the x-component of tension, and that it would be the only other force, including friction at the pivot point, in the x-direction.

    The chosen pivot point was the point where the bar made contact with the ground.
  2. jcsd
  3. Nov 17, 2013 #2


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    Please post your working
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