Bending moment formula?

  1. 1. The problem statement, all variables and given/known data
    what is the bending moment formula? is it related to the pure bending formula? what's that?


    2. Relevant equations



    3. The attempt at a solution
    is the formula 1/p=M/EI?
     
  2. jcsd
  3. Defennder

    Defennder 2,616
    Homework Helper

    There's a particular physical setup associated with the bending moment of a small section dx of a beam under gravity. The formula would depend on how you setup and balance the forces and torque on that section. Perhaps if you describe it, the homework helpers here could help you figure it out.
     
  4. i am finding the bending moment of a rectangular beam of plywood. the dimensions change due to altering the variables throughout the experiment.
     
  5. Defennder

    Defennder 2,616
    Homework Helper

    Yes, but how do they change? You have to be more explicit here, otherwise I don't think anyone can help. Try posting the question from the textbook or notes.
     
  6. its not a question it is a part of a physics assignment of beam deflection.. i am trying to show for the formula (force x length^3)/(4 x young’s modulus x breadth x thickness^3) was derived. i know it was done through integration and the combining of the bending moment formula and the Torque formula (T=fr)...
     
  7. Suppose we have the situation in the picture.

    1.PNG

    We get:

    [tex] EIv_{xx} = -FL+Fx [/tex]

    or after two integrations:

    [tex] EIv(x) =F \frac{(x-L)^3}{6} +C_1x +C_2 [/tex]

    From this point on I leave it to you....
     
    Last edited: Jun 18, 2008
  8. stewartcs

    stewartcs 2,279
    Science Advisor

    Start with the Euler-Bernoulli Beam equation, and specifiy your boundary and loading conditions.

    http://en.wikipedia.org/wiki/Euler-Bernoulli_beam_equation

    CS
     
  9. nvn

    nvn 2,124
    Science Advisor
    Homework Helper

    Amy54 wrote: "What is the bending moment formula?"

    d(theta)/dx = M(x)/(E*I), where theta = beam rotation, and M(x) = moment as a function of x.

    Amy54 wrote: "Is it related to the pure bending formula? What's that? Is the formula 1/rho = M/(E*I)?"

    Nice work, Amy54. Yes, that is the pure bending formula. For small theta, d(theta)/dx = 1/rho.
     
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