Hi Heathen
Just to jump in here.
I'm a structural/stress engineer and deal with this kind of problem regularly.
For clarity (and correct me if I'm wrong here Taz)
The triangle at point A represents a "Simple Support" [edit: a simple support allows rotation but not translation] and the circle at point B represent a support that allows a horizontal translation and prevents vertical translation [edit: and allows rotation].
Indeed, and this is part of
your "common knowledge" even though not everyone knows it or understands your explanation ...
This is part of the "technical language" of structural/stress engineering, where the symbols used represent whole phrases and contexts that someone not educated as an engineer do not know and have no way of knowing.
For instance, I can open my 4th edition
Steel Manual (1967) to page 2-122 and look at diagram #9 and see this very problem, along with the formulas for stresses and deflections. (if you don't have the same edition, the page and diagram number are likely different, but the diagram will be the same).
We also know that these diagrams are
idealized renditions of common problems (hence the triangle pin and roller at the ends) and that assist in finding reasonable solutions.
Message 39: He has perfectly shown how people with little or no knowledge of the subject at hand still feel they can wade in and point out what they see to be deficiencies in the diagram and therefore dismiss the question as nonsense.
When in fact to someone who knows the subject matter, the diagram is clear, consise and as has been shown in this thread, makes the point that Taz wanted to make quite well.
Indeed. This is why learning the technical "language" of a field is critical if you are going to discuss it intelligently.
Enjoy.