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Moment-beam under bending momen?

  1. Sep 9, 2005 #1
    A beam is under bending. Let us take a small part of a beam with length x. It has end A and end B. At end A the bending moment is M1 & shear force is S1 and at end B the bending moment is M2 & shear force is S2.
    Let me take the moment equilibrium for this element about B.

    M2-S2-M1+S1=0.

    I need clarity in adding M1 in the above equation. Actually M1 acts with A as the centre. But why this is included while taking moment about B.
     
  2. jcsd
  3. Sep 9, 2005 #2

    Astronuc

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    Staff: Mentor

    M is a moment or torque, which is not a force, but the effect of a force applied at some moment arm.

    M has units of F-d (force - distance, e.g. N-m or ft-lbm).

    In a static beam situation, the sum of the forces must = 0, and the sum of the moments = 0.

    Here is a good reference on beam mechanics (statics) -
    http://physics.uwstout.edu/StatStr/statics/Beams/beam41.htm#Topic%204.1%20Shear%20Forces%20I [Broken]

    and

    http://physics.uwstout.edu/StatStr/statics/ [Broken]
     
    Last edited by a moderator: Apr 21, 2017 at 7:36 PM
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