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## Re: [TowerTalk] Friction (was Mast Clamps)

 To: "Art Boyars" , Re: [TowerTalk] Friction (was Mast Clamps) "K8RI on Tower talk" Fri, 3 Mar 2006 19:18:59 -0500
 ``` > 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 just dug out my old Calc based physics book trying to find the names and formulas. When it comes to sliding somehting it is a two stage problem as it takes more force to start the movement than it does to continue the movement. Of course you can use calculus . It's amazing. I don't think I could now answer enough of those problems to even pass the course and I have a math minor. I never had to use any of the math since I graduated. > > 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. Just think of it as a lathe with a very wide cutting bit. > > 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! And if you are working with DC. One of our exercises was to calculate the average speed of the free electrons in a conductor of a given size for a given current. I couldn't do a derivative or intergral today if my life depended on it. Roger Halstead (K8RI and ARRL 40 year Life Member) N833R - World's oldest Debonair CD-2 www.rogerhalstead.com > > Back to my towerless lurking. > > 73, Art K3KU > _______________________________________________ > > > > _______________________________________________ > TowerTalk mailing list > TowerTalk@contesting.com > http://lists.contesting.com/mailman/listinfo/towertalk > _______________________________________________ _______________________________________________ TowerTalk mailing list TowerTalk@contesting.com http://lists.contesting.com/mailman/listinfo/towertalk ```
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