Re: [ATM] Use of bearings in (static) mirror cells

["john sherman" <atm@mail.johnspics.com>]

Hi List,

>The fundamental difference between friction 
>and flexure is that the first dissipates 
>energy while the second stores energy, 

Hey, I like this explanation! Of course, it is the reason that a flexure joint pushes back when moved, and a normal cell doesn't. The dissipation of energy allows the mirror to sit in a normal cell the way "it wants to". 

>Stiction is not friction.

Right, stiction is a combination of forces. Ignoring the force required to overcome the inertia of the object(s), two objects tend to "stick" together from friction and Van der Walls forces. The electrical forces can be stronger in some situations, and seem to build over time (which friction does not), and have to be broken to create the relative motion. Also there are probably other reasons I don't know of. 

Does a flexure have stiction? I read that there are always Van der Walls intermolecular forces between molecules in proximity, whether they are part of a solid mass or two individual masses in contact. 

So I have trouble believing that these forces, combined with friction, don't cause stiction in a solid flexure joint. It should require a force to initiate movement of the joint from its optimum position. But then, that's just me.

John







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