Bending moment formula?

  • Thread starter Amy54
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  • #1
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Homework Statement


what is the bending moment formula? is it related to the pure bending formula? what's that?


Homework Equations





The Attempt at a Solution


is the formula 1/p=M/EI?
 

Answers and Replies

  • #2
Defennder
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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.
 
  • #3
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i am finding the bending moment of a rectangular beam of plywood. the dimensions change due to altering the variables throughout the experiment.
 
  • #4
Defennder
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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.
 
  • #5
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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)...
 
  • #6
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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)...

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:
  • #7
stewartcs
Science Advisor
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Homework Statement


what is the bending moment formula? is it related to the pure bending formula? what's that?


Homework Equations





The Attempt at a Solution


is the formula 1/p=M/EI?

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
Science Advisor
Homework Helper
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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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