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# mudzm9 - Muddy Card Responses Lecture M9 Why do the bars...

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Muddy Card Responses Lecture M9 Why do the bars extend axially? Since the bars in a truss only carry axial forces and have a constitutive law d =FL/AE (i.e. Hooke's law) the extension of the bar must be aligned with the direction of the bar. In addition there is a rotation. How are the displacement diagrams useful? Are they just to visualize relative movements They not only allow one to quantify the relative movements, but also to quantify them as well. If you draw the displacement diagram accurately you can measure the displacements of it. Or use trigonometry to calculate the displacements. It might be easier to follow displacement diagrams if you drew it in class. It was a lot easier to understand when I just imagined deriving it. Good point. I think that this is one of those techniques that looks a bit intimidating, but is actually quite straightforward when you apply it. Is it necessary to draw the displacement diagram you made to solve for point displacements? Is it more helpful than confusing? Obviously I think that it is helpful otherwise I would not be doing it!. As mentioned above, if you actually try to work out a problem using it I think that you will find that it is not as bad as it looks. In the problem that we did in lecture today did AE =1 for all of the bars . Sort of, in the notes I normalized all the bar extensions by PL/AE – so that they were just numbers. I could have set AE= 1, but this would have been less physically realistic. I didn’t understand 100% how to draw a deflection diagram when starting up. The ?????? (illegible). We will do a little more on this in class today and there are a couple of homework problems to allow you to practice further. No mud. For the test next Friday are we going to cover block 1 only, or will we cover all the lectures up until the test. ? No just block 1 – i.e todays lecture, and the material covered in this week’s homeworks (i.e. to M10).

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## This note was uploaded on 02/20/2012 for the course AERO 16.02 taught by Professor Charlescoleman during the Winter '12 term at MIT.

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mudzm9 - Muddy Card Responses Lecture M9 Why do the bars...

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