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Force in a static member

  1. Sep 6, 2010 #1
    If I have a beam tilted at an angle with a weight hagning off of one end and it is fixed on the other (see attachment), my teacher says that I need to resolve the force to find the force in the beam. However, it does not make sense to me that the force in the beam increases as the angle decreases. At an angle of 1 degree the beam has a very large internal force that "goes away" once the angle becomes zero. The way I am determining the force in the beam is: since the weight creates a force in the y-direction the force in the beam is the weight divided by the sine of the angle. This just doesn't sense. What am I missing?

    Attached Files:

  2. jcsd
  3. Sep 6, 2010 #2
    Your post seems a trifle muddled.

    You say that you are calculating a force that equals a constant divided by the sine of an angle.
    Yet you also express suprise that the calculation grows yields an increasing result as the angle decreases.

    Since the sine is always less than 1 and decreases with decreasing angle why is this suprising?

    I am not sure how you are modelling your beam.
    Have you considered any other load imposed on the beam as a result of the geometry, in particular have you considered moment equilibrium?
  4. Sep 6, 2010 #3
    I understand that there will be a moment applied to this beam due to the weight hanging off the end.

    It seems counterintuitive that the compression in the beam increases as the angle decreases. I know what the math shows; it just doesn't seem correct that at a 90 degree angle the compression would be 100 lbs (assume the weight is 100 lbs), but at an agle of 1 degree the compression would be 5729.8 lbs. 100 divided by sine of 1 degree. Am I truly solving for the compression in the member correctly? The compression increases by 57 times the original? In my mind the compression of the beam should decrease as the angle approaches 0.
  5. Sep 6, 2010 #4
    Draw a free body diagram for the tip of the beam, decomposing W and check where is theta.
    Last edited: Sep 6, 2010
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