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From: kvj@rhi.hi.is (Kristjan Valur Jonsson)
Newsgroups: comp.sys.acorn
Subject: Re: Archimedes keyboard
Keywords: Keyboard, defunct
Message-ID: <2847@krafla.rhi.hi.is>
Date: 28 Feb 91 10:59:44 GMT
References: <1991Feb19.160812.20483@cns.umist.ac.uk> <2313@cybaswan.UUCP> <1991Feb21.143445.22959@fwi.uva.nl> <2835@krafla.rhi.hi.is> <2837@krafla.rhi.hi.is>
Organization: University of Iceland
Lines: 42

In <2837@krafla.rhi.hi.is> thsa@rhi.hi.is (Thorvaldur S Arnarson) writes:

>In article <2835@krafla.rhi.hi.is> kvj@rhi.hi.is (Kristjan Valur Jonsson) writes:
>[stuff deleted]

>|If you look at a state of the art mouse these days, they all seem to
>|have these new light types of balls.  I suspect that the reason is that
>|lighter balls have less inertia (can't remember the correct term for this
>|"axial inertia") and therefore better response.  You must be thinking about
>|an old Macintosh mouse.

>Utter nonsense!!!!!  How about the new Logitec mouse, thats fairly state
>of the art.  If the coupling between the ball and the direction sensing
>mechanism is frictionless the weight of the ball does not matter.  If there
>is friction (yes this is not a textbook on elementary physics!) the weight
>matters as increased weight decreases the 'sensing friction' vs 'friction 
>between ball and surface' ratio.
>Inertia???!  How fast does your hand/mouse change directions?

True, maximum axial acceleration of the ball without slipping is independend
of mass and inversely proportional with it's radius.
	Since the ball is resting on the table and not being forced down, all
internal friction will be proporional to the horisontal force applied, which
in turn is proportional to it's mass.  Of course, there is some constant
internal friction regardless of acceleration since the sensors/rollers are
spring loaded.  So, I must aggree that a heavier ball would increase the 
(surface fric.)/(internal fric.) ratio.   But why then has the trend in mouse
design been towards lighter balls?  Surely it would be easy enough to make
them heavy as rocks.  The Logitech mice connected here (vetrarholl) are as
new as they get but are of the same light type as Arc mice.

I hope someone knows (preferably mouse designers) :-0
                                                   ^ look, an indifferent
                                                     smiley!

>Best regards,
>  Thorvaldur S. Arnarson.
>-- 
>  Regards,
>  Thorvaldur S. Arnarson

Rgds, Kristjan