Re: [ATM] Basic mirror support question...

["Jerry Reddell" <jerry.p.reddell63@sbcglobal.net>]

I agree.

The fact that only three points are needed to define a plane does not mean
that only three points can or will be in the plane....Many can be in the
same plane and many points on two objects with surfaces in the same plane
can be touching.

>From a practical standpoint, there is enough flexibility / compressibility
in real materials  that essentially all points will be touching.

Jerry P. Reddell

-----Original Message-----
Of Arjan te Marvelde

> Basically it surprises most people that two plan
> surfaces no matter how smooth will only touch at three
> places.  From math we know that three points define a
> plane.  The two plans will define a third plane where
> they touch.  They will touch at the mutual high points
> on their surfaces.

This is not generally true, there maybe four points. Consider a chair on a
bumby floor: it will rest on three legs. But by rotating the chair, while
keeping those three legs in contact, ultimately the fourth will touch as
well.
OK, it's a metastable situation, not likely to be maintained in reality, but
stil...

Also if one of the surfaces is slightly cylindrical, it will be
kinematically defined with four supports.

Cheers,
Arjan te Marvelde

_______________________________________________
ATM mailing list http://www.atmlist.net/


_______________________________________________
ATM mailing list http://www.atmlist.net/