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FW: ATM New measurements of Coef of friction
> -----Original Message-----
> From: Arjan te Marvelde (ELN)
> Sent: Thursday, February 21, 2002 2:10 PM
> To: 'rguinamard@infonie.fr'
> Subject: ATM New measurements of Coef of friction
>
>
> Hi Raphael,
>
> I like it that you question the prevailing common
> understanding of Teflon and Ebony star being the friction
> walhalla. There will be more material combinations possible
> and also specific situations that may do as well with them.
>
> Still i have questions about your measurements:
> -Q- You measure a dependency of kinetic COF from the applied
> load which does not comply with friction theory. Within
> limits the COF is a constant for a combination of materials,
> and should be independent of load. The friction force is
> proportional to the normal force on the surface, by the
> kinetic COF. Is there any chance that the ^0.17 is a
> measurement artifact?
> -Q- How can you measure a static COF that is smaller than the
> kinetic COF?
>
> And also some remarks:
> Applying friction theory, increasing the teflon surface above
> a certain threshold does not help to get a lower friction force.
> The hreshold is determined by the amount of deformation in
> the teflon. So the small pebbles in Ebony star in fact
> decrease the effective contact area, and may therefore
> increase the friction force because small dents are pushed in
> the teflon. Here maybe also the teflon thickness and
> underlying surface are important.
>
> Furthermore, since the friction force is proportional to the
> normal force on the plane of friction only, increasing the
> angle between teflon pads will increase friction.
>
> The force you experience when pushing the telescope equals
> the total friction force divided by the ratio of trunnion
> radius and pushing point radius. So the smaller your
> trunnion, the lower the experienced force. But of course,
> this force is also experienced by the various eyepieces and
> the wind...
>
>
> For limits of the friction model see:
> http://hyperphysics.phy-astr.gsu.edu/hbase/frict3.html#ass
> or for friction theory in general:
> http://hyperphysics.phy-astr.gsu.edu/hbase/frict.html#fri
>
> I hope that this all makes sense, and adds to understanding
> in general,
> ... Arjan te Marvelde
>