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Which types of elasticity are involved?

  1. Nov 17, 2009 #1
    1. The problem statement, all variables and given/known data

    A pole projects horizontally from the front wall of a shop. A 6.1-kg sign hangs from the pole at a point 2.2 m from the wall.

    (a) What is the torque due to this sign calculated about the print where the pole meets the wall?
    (b) If the pole is not to fall off, there must be another torque exerted to balance it. What exerts this torque?
    (c) Discuss whether compression, tension, and/or shear play a role in part (b).

    2. Relevant equations


    3. The attempt at a solution

    I'm stuck on (c).

    For part (b) I got that one end of the wall (the one farther from the sign) exerts a downward force and the other end (closer one) exerts an upward force.

    So for (c), I believe shearing is involved. But according to the answer, all three types (tension, compression, and shear stress) are present. I'm not sure why this is true. Does it have to do with the two ends of the wall exerting forces of different magnitudes? According the book, shearing occurs when the opposite ends are under forces of same magnitude.
  2. jcsd
  3. Nov 17, 2009 #2


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    Yes, and when the equal and opposite forces are separated, you get shear and a bending moment. A bending moment produces tensile and compressive stresses on the top and bottom of the pole.
  4. Nov 24, 2009 #3
    Thanks for the reply.

    Is it correct to say that shearing takes place only in the wall while compression and tension take place in the whole pole because the whole thing is being bent?
  5. Nov 24, 2009 #4


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    No, shear isn't limited to the wall connection. Draw a shear & bending moment diagram if you want to confirm this.
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