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Who Says There Is No MA Angle On 9/11?

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    #61
    Originally posted by Da Pope View Post
    If your masses are assumed RIGID as you did in your high skool example, then you are assuming that they CANNOT DEFORM. An increase in internal energy IS A FORM OF DEFORMATION.
    Yes, intuitively we all understand that a rigid body cannot rebound in any classical sense. I'm requiring you to be more precise about the definition of "Rigid". What you really mean is that the rebound distance can not correspond to any real number. Classically, this is the same thing as saying the rebound distance is 0. This is naive, however, and leads directly to the contradiction "This object, which can not deform, is storing 25J is an internal vibratory (deformational) state." Remember that I am not the one that sets up physics problems like the one I mentioned; I am not the one telling students, collegues, or whoever that energy missing from the KE calculation is to be found in the (deformational) internal states of the object, while the object is rigid and can't deform. Physicists are. I did not invent the idea of rigid body inelastic collision, I just pointed out that there is a paradox implied, and asked you to take a stab at resolving it.

    The resolution of the paradox requires us to be precise about what we mean when we say "An object is perfectly 'rigid' when it can not deform in any way." So, let us say instead "An object is perfectly 'rigid' when, for every pair of points on or inside its perimeter, the distance between them remains constant with respect to time, where "remains constant" means 'does not differ by any real-number amount.'

    As I pointed out the question doesnt make any physical sense.
    Tell it to the people using rigid body inelastic collisions to model physical phenomena.

    On the one hand you say deformation cannot happen and then later (after it being pointed out in my earleir post) claim it does due to an increase in internal energy.
    That's right, it's an apparent paradox.

    Your intellectual Gong Sau was at best a badly poised high skool example used to teach a concept in a grossly oversimplified way.
    Yes the paradox is present in material taught to high school students. Does that mean I am one of them?

    Since you're more interested in claiming the question is stupid because there is an apparent paradox in play, than in attempting to resolve it, I'll do the work for you:

    If we think for a moment of highly (but not perfectly) 'rigid' objects as doing all of their deformational work in the form of a "ring" of certain pitch, for objects of differing 'rigidity' but identical mass, that ring will tell us the deformational energy resulting from a collision in terms of it's period/frequency/pitch. As the deformability (defined as the maximum difference two points on the object may display) of the colliding object becomes vanishingly small, so does the frequency of the "ring". An object with infinitesimal deformability is called (perfectly) rigid, and any "missing" energy will be found in the infinitesimal frequency (and amplitude) of its ring.

    Another way of stating this is that the slope of the stress-strain curve approaches infinity as deformability goes to zero.

    As they say, :owneddanc
    Last edited by Matt Phillips; 3/08/2010 12:43pm, .
    Now darkness comes; you don't know if the whales are coming. - Royce Gracie


    KosherKickboxer has t3h r34l chi sao

    In De Janerio, in blackest night,
    Luta Livre flees the fight,
    Behold Maeda's sacred tights;
    Beware my power... Blue Lantern's light!

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      #62
      Originally posted by Da Pope View Post
      So err you had sensors placed all over the Trades Centre's internal structure?
      I haven't done any measurements of the tower collapses. This is from the 35 brick break vid.

      You captured some data on the crack propagation through the structural supports of the buildings?
      See above.

      You had some manner of measuring the stress energy at critical structural points in the supporting structures induced by an commercial jet plane hitting it?
      This has been done by NIST and others, but it is irrelevant to breaking bricks.

      Or did you deduce all that data from a video camera?

      :shock:

      FTR, you're responding to this:
      Originally posted by War Wheel
      Update: I did an analysis of the audio track for the 35 brick break vid, and I can report that there is slight, but measurable acceleration.
      Your problem isn't that you're stupid, it's that you can't read.
      Now darkness comes; you don't know if the whales are coming. - Royce Gracie


      KosherKickboxer has t3h r34l chi sao

      In De Janerio, in blackest night,
      Luta Livre flees the fight,
      Behold Maeda's sacred tights;
      Beware my power... Blue Lantern's light!

      Comment


        #63
        Originally posted by War Wheel View Post
        Tell it to the people using rigid body inelastic collisions to model physical phenomena.
        You brought it up!

        The inelastic rigid body collision example is a teaching tool used as a stepping stone to more complex phenomena. Get a grip!

        Nobody who has studied the mechanics of materials in any depth would consider the example as anything but something you taught children.

        Originally posted by War Wheel View Post
        That's right, it's an apparent paradox.
        See above.

        To be honest you are not displaying any clear understanding of the basic principles behind structural mechanics. I am not saying you dont have them, just that so far it isnt apparent.

        Comment


          #64
          Originally posted by War Wheel View Post
          Your problem isn't that you're stupid, it's that you can't read.
          No I am stupid as well.

          Comment


            #65
            Originally posted by Da Pope View Post
            You brought it up!

            The inelastic rigid body collision example is a teaching tool used as a stepping stone to more complex phenomena. Get a grip!

            Nobody who has studied the mechanics of materials in any depth would consider the example as anything but something you taught children.
            There are many folks using RBIC(rigid body inelastic colision) models in Robotics, Computer Animation, Physical Simulation, pure Mathematics, etc. Just because something is taught to high school students does not mean it is lacking in application to real world research. Even the most complex proofs in Mathematics make some use of high school algebra.

            Here are a few papers recovered by putting 'rigid body inelastic collision' into the Google machine:

            AN IMPLICIT TIME-STEPPING SCHEME FOR RIGID BODY DYNAMICS WITH INELASTIC COLLISIONS AND COULOMB FRICTION (http://www3.interscience.wiley.com/j...16417/abstract)

            QUALITATIVE RIGID BODY MECHANICS
            (http://people.csail.mit.edu/hes/publ...ualitative.pdf)

            RIGID BODY SIMULATION USING IMPULSES
            (http://files.slembcke.net/misc/RigidBodies.pdf)


            Last time I checked, most researchers in Real Time Simulation were HS graduates.


            To be honest you are not displaying any clear understanding of the basic principles behind structural mechanics. I am not saying you dont have them, just that so far it isnt apparent.
            I have no background in structural mechanics at all. What I do is meet with a physicist once a week to check my understanding of the material I'm interested in, but I have not had any formal instruction in structural mechanics. I'm a computational biologist, damnit, not a brick layer!

            Do you have some specific response to my solution to the 'paradox'? Do you have any thoughts of your own on the matter, or are you content to just claim that there is no paradox because it will never come up outside the classroom?

            What you're not showing is analytical ability. I'm sure you have it, but you're not showing it.
            Last edited by Matt Phillips; 3/08/2010 1:36pm, .
            Now darkness comes; you don't know if the whales are coming. - Royce Gracie


            KosherKickboxer has t3h r34l chi sao

            In De Janerio, in blackest night,
            Luta Livre flees the fight,
            Behold Maeda's sacred tights;
            Beware my power... Blue Lantern's light!

            Comment


              #66
              Originally posted by War Wheel View Post
              Another way of stating this is that the slope of the stress-strain curve approaches infinity as deformability goes to zero.
              As I am furiously trying to avoid doing any work I will respond to this.

              Outside of your little inductive reality, science has discovered this truly amazing piece of empirical knowledge known as thermodynamics......

              :violent1:

              Comment


                #67
                Originally posted by Da Pope View Post
                science has discovered this truly amazing piece of empirical knowledge known as thermodynamics......
                I'm listening...

                :violent1:
                Lol!
                Now darkness comes; you don't know if the whales are coming. - Royce Gracie


                KosherKickboxer has t3h r34l chi sao

                In De Janerio, in blackest night,
                Luta Livre flees the fight,
                Behold Maeda's sacred tights;
                Beware my power... Blue Lantern's light!

                Comment


                  #68
                  OK I had a quick look at the rigid body papers. I take your point it is used outside of the high skool class room, but it is done so that they can simplify their models in order to not deal with the material properties of the mechanisms.

                  My solution to the paradox is that it doesnt actually exist. No such material has been discovered that displays perfect rigidity!

                  Comment


                    #69
                    Originally posted by Da Pope View Post
                    OK I had a quick look at the rigid body papers. I take your point it is used outside of the high skool class room, but it is done so that they can simplify their models in order to not deal with the material properties of the mechanisms.
                    Yes, that is the only reason I can think of for using them.

                    My solution to the paradox is that it doesnt actually exist. No such material has been discovered that displays perfect rigidity!
                    Yes, and the infintesimals used in the Calculus are infinitely larger than the Planck length. But that doesn't mean there is no application of Analysis to problems of motion.

                    The issue originally came up in a forum about Real Time Simulation. I never said it had a physical interpretation. How you resolve the paradox is important because it affects how you interpret your simulation results.
                    Now darkness comes; you don't know if the whales are coming. - Royce Gracie


                    KosherKickboxer has t3h r34l chi sao

                    In De Janerio, in blackest night,
                    Luta Livre flees the fight,
                    Behold Maeda's sacred tights;
                    Beware my power... Blue Lantern's light!

                    Comment


                      #70
                      This is causing me problems because I come from the materials side of things. Sure if you are dealing with mechanisms where the forces involved arent going to deform any part of your assembley then by all means treat your materials as rigid.

                      But if you are going to get into failure of structures and propagation of stress waves etc I just dont see why you would do such a thing. Failure of a material or how stress travels through a structure depends on the materials properties which will never be perfectly rigid. If they were then it wouldnt fail.

                      Comment


                        #71
                        Originally posted by Da Pope View Post
                        This is causing me problems because I come from the materials side of things.
                        I got that, and I'm glad to have someone with that background in the conversation.

                        Sure if you are dealing with mechanisms where the forces involved arent going to deform any part of your assembley then by all means treat your materials as rigid.

                        But if you are going to get into failure of structures and propagation of stress waves etc I just dont see why you would do such a thing.
                        Actually I only introduced the question so we would have a chance to spar. it has no relevance to the OP in the context I asked it.

                        Failure of a material or how stress travels through a structure depends on the materials properties which will never be perfectly rigid. If they were then it wouldnt fail.
                        Emphasis mine.

                        The components won't fail, but the structures made from them can.

                        YouTube- Blender physics test (building collapse)
                        YouTube- Testing Blender physics
                        Now darkness comes; you don't know if the whales are coming. - Royce Gracie


                        KosherKickboxer has t3h r34l chi sao

                        In De Janerio, in blackest night,
                        Luta Livre flees the fight,
                        Behold Maeda's sacred tights;
                        Beware my power... Blue Lantern's light!

                        Comment


                          #72
                          Haha Ok I'm with you.

                          The main difference between those examples and a building is that a building's "parts" are stuck together and come unstuck due to stress waves causing cracks (voids, discontinuities etc) in the materials that were at one time joined together.

                          It is the properties of these joins that will determine the failure ie the constitutive make up of the materials making and joining up the structure including the shape of the structure.
                          Last edited by Da Pope; 3/08/2010 3:12pm, .

                          Comment


                            #73
                            Originally posted by Da Pope View Post
                            Haha Ok I'm with you.

                            The main difference between those examples and a building is that a building's "parts" are stuck together and come unstuck due to stress waves causing cracks (voids, discontinuities etc) in the materials that were at one time joined together.
                            You got it.

                            So, getting back to the topic: It seems there is some small, but measurable acceleration in the brick breaking vids. I'll post the curve I derived from the audio data later tonight.
                            Now darkness comes; you don't know if the whales are coming. - Royce Gracie


                            KosherKickboxer has t3h r34l chi sao

                            In De Janerio, in blackest night,
                            Luta Livre flees the fight,
                            Behold Maeda's sacred tights;
                            Beware my power... Blue Lantern's light!

                            Comment


                              #74
                              Hold on the failure of a stack of tiles (bricks) is in no way comparable to the collapse of the WTC!

                              Comment


                                #75
                                YouTube- Hamster Wheel

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