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[TowerTalk] Friction (was Mast Clamps)

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Subject: [TowerTalk] Friction (was Mast Clamps)
From: "Art Boyars" <>
Date: Fri, 03 Mar 2006 17:13:52 -0500
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In the long and useful thread about mast clamps that slip under torque, several 
contributors have discussed the friction between the clamps and the mast.  I'll 
point out that the linear relationship for friction force F=mu*N is only a 
model (an approximation) that works pretty well in most cases -- but not in all 
cases.  Indeed, we commonly hear about "static friction" and "sliding 
friction", because the simple linear model neededd a little modification.  I've 
heard some Mech E's mention "sticktion" (sp?), and it sounded like they meant 
something other than static friction.

I recall reading about race cars that cornered so well because they achieved 
mu>1, which was said to violate the linear model.

And, for sure, if the mast clamps have those groovy little cuts to dig into the 
mast, the "friction" is not going to be linear with the clamping force.

We use linear models lots of places because: a) they are accurate enough; b) we 
can handle the math.

And if you'll indulge me, here's a parallel example from the Real World 
(electricity).  Perhaps you have seen Ohm's Law in "point form": is J=sigma*E.  
(It's the same thing as I = (1/R)*(V):  current density = conductivity*Electric 
field.)  Well, in actuality (as I read somewhere many years ago), this Law is 
not true for all materials.  It does holdsfor a broad class of conducting 
materials, and they are called ... Ohmic conductors!

Back to my towerless lurking.

73, Art K3KU

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