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234   Chapter Nine

            Example 9.1: Brushing Teeth
            If we use a toothbrush correctly, and our teeth get cleaned properly, then we call
            this brush action a normal useful action. We can illustrate this by the following
            functional analysis diagram:

                                       Brush
                           Toothbrush           Teeth
                                       mech.
            However, if we use the toothbrush too gently and do not brush long enough, or
            we use a worn toothbrush, then our teeth will not get enough cleaning. In this
            case, we can use the following functional analysis diagram:

                                       Brush
                           Toothbrush           Teeth
                                       mech.
            Clearly, this is a case of an insufficient useful action.
            If we use a very strong toothbrush and brush our teeth with much force and big
            strokes, then our gums will get hurt, and so will our teeth. We can use the
            following functional analysis diagram to describe this situation:

                                      Brush
                        Toothbrush                Teeth
                                        Wear

                                     Tear         Gums

            That is, the toothbrush delivers excessive brushing action to the teeth. The
            excessive toothbrush action is harmful since it tears the gums and makes them
            bleed. The teeth also may deliver a harmful action, by causing wearing of the
            toothbrush.

        Functional Modeling and Analysis Example
        Figure 9.2 is a schematic view of an overhead projector. Figure 9.3 shows a
        graph of the functional modeling and analysis diagram for the whole system.

        In this functional analysis graph, E stands for electric field and M stands for
        mechanical field. In this example, there are many chains of action; that is,
        an object can be another object’s subject. Then we have a sequence of
        subject-action-object-action chains. Each chain describes a complete
        function. We can identify the following functions:
          1. From electric power to image to screen, that is, the function of pro-
             jecting an image in the film onto the screen. We can think of this as the
             main basic function.
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