Re: Friction Effects in Piping Systems

From: <Christopher>
Date: Tue Apr 22 2003 - 13:21:00 EDT

>In my opinion, the friction forces never disappears from the system. They
>are always present. Does this means that there is no friction when we are
>standing on our feet?

Think about standing vertically without moving there are no friction forces until there is an external force applied--then friction acts to resist the external force. It makes for a highly indeterminate situation--much more complicated than simply imagining what the normal force is and multiplying by a coefficient from a handbook.

The point I was trying to make is that in many cases frictional restraint can't be maintained because the normal force varies from time to time and so the frictional restraint is overcome. There are a lot of situations which absolutely require consideration of friction, but even those don't involve a precise calculation because precise calculation really isn't possible. The best example I know of is the bolted joint. Preloading a bolt isn't possible without friction--the nut would simply spin right off the threads and drop to the ground. But the best you can do is guess at the friction coefficient between the threads, and you tighten the fastener according to someone's best guess, knowing that even that guess will have an error of about 30% if you're using a torque wrench.

No one's saying always ignore friction--just think about what happens in the real world and make an intelligent judgement.

Christopher Wright P.E. |"They couldn't hit an elephant at <a href="/group/PipingDesign/post?postID=y5hyOS50On72QFMdRmdyjDk-fZIEC3aLsNjl-NdL5vbASJBmGv-YjLZqPvXoz5Z6WWrJn0I68GKlze9o">chrisw@skypoint.com</a> | this distance" (last words of Gen.

___________________________| John Sedgwick, Spotsylvania 1864)

<a href="http://www.skypoint.com/~chrisw">http://www.skypoint.com/~chrisw</a> Received on Tue Apr 22 13:21:00 2003