Dismiss Notice
Join Physics Forums Today!
The friendliest, high quality science and math community on the planet! Everyone who loves science is here!

Young's modulus of the material

  1. Oct 8, 2004 #1
    Hello again,
    I dont understand how to derive equations.
    C = YI / r

    Y = Young's modulus of the material
    r = radius of curvature of the neutral surface
    I = geometrical moment of inertia of the cross section of the beam
    C = bending moment

    I = wt^3 / 12

    I = moment of inertia
    w = width of rectangular beam
    t = thickness of rectangular beam

    Koenig's Apparatus
    theta = h / 2(d+2D)

    theta =angle of deflection
    d = distance between mirrors on rectangular beam
    D = distance between mirror(mirror which is closer to telescope) to scale
    h = difference between the reading of scale

    Thank you :D
    i'm not good wif deriving equations :(

    oh, and one more
    have a question asking me to arrange three beams in the order of their radius of curvature when Y, C and A are equal, the three beams are Round beam, Square beam, H-shaped beam.
    i just need to find equations for moment of inertia for these shapes?
  2. jcsd
  3. Oct 9, 2004 #2
    for arranging the order for three beams
    Round beam, i have I = A^2 / 12
    Square beam, i have I = A^2 / 12

    with equation C = YI / r
    Round beam will have r = YI / C = [Y*(A^2 / 12)] / C
    Square beam will have r = YI / C = [Y*(A^2 / 12)] / C

    but i dont know how to convert the H-shaped beam
    i found out, for H-shaped beam
    A = HB + hb
    I = (BH^3 + bh^3) / 12


    Attached Files:

    Last edited: Oct 9, 2004
  4. Oct 9, 2004 #3
    i've derived the other formulae
    but i'm still stuck on this one, Koenig's Aparatus formula
    here's a picture of it with the formula need to derive into

    theta = h / [2(d+2D)]

    Attached Files:

Share this great discussion with others via Reddit, Google+, Twitter, or Facebook