1. Not finding help here? Sign up for a free 30min tutor trial with Chegg Tutors
    Dismiss Notice
Dismiss Notice
Join Physics Forums Today!
The friendliest, high quality science and math community on the planet! Everyone who loves science is here!

Torque Equilibrium question

  1. Dec 6, 2013 #1
    1. The problem statement, all variables and given/known data

    A uniform sphere of weight mg and radius r0 is tethered to a wall by a rope of length ℓ. The rope is tied to the wall a distance h above the contact point of the sphere, as shown in the figure.(Figure 1) The rope makes an angle θ with respect to the wall and is not in line with the ball's center. The coefficient of static friction between the wall and sphere is μ.

    To find: a) Frictional force in terms of r0, m, h, theta
    b) Suppose the sphere is on the verge of slipping. Derive an expression for coefficient of friction in terms of h and theta.


    2. Relevant equations
    Sum(Forces) = 0
    Sum(Torques) = 0


    3. The attempt at a solution
    From Sum(Forces) = 0:
    Ff = mg - TCosθ
    For torques:
    This is where I am confused:
    Considering torques with respect to the point of junction between the string and the wall:
    In counterclockwise: torque due to tension TLCosθ
    In clockwise: torque due to friction?

    I'm at a conceptual misunderstanding here!
     
  2. jcsd
  3. Dec 6, 2013 #2
    Where is Figure 1?
     
  4. Dec 6, 2013 #3
    Here it is:
     

    Attached Files:

  5. Dec 6, 2013 #4
    Because friction is applied at the junction, it cannot have any torque with respect to the junction. But there is another force at a distance from the junction, it is even shown in the figure.
     
  6. Dec 6, 2013 #5
    Alright, so that would be the torque due to the force of gravity. What I don't get is how I determine the reference point for calculating the torques. Right now I am using the rope-wall junction.
     
  7. Dec 6, 2013 #6
    It does not matter. Any point will do. Choose one that makes the calculations easiest.
     
Know someone interested in this topic? Share this thread via Reddit, Google+, Twitter, or Facebook

Have something to add?
Draft saved Draft deleted



Similar Discussions: Torque Equilibrium question
Loading...