# RE: Footing sliding resistance - Friction

• To: <seaint(--nospam--at)seaint.org>
• Subject: RE: Footing sliding resistance - Friction
• From: "Eli Grassley" <elig(--nospam--at)psm-engineers.com>
• Date: Wed, 22 Jun 2005 10:17:24 -0700
```We are talking about the *static* friction of a rigid mass against a
surface.  Not the kinetic rolling resistance of a deformable object like a
tire. That's an entirely different process of forces going on.

Open up a freshman level physics textbook and look at the equation for
static friction... F = mu * W
That hasn't changed in well over 200 years.

~~ Eli ~~

-----Original Message-----
From: John Riley [mailto:jpriley485(--nospam--at)yahoo.com]
Sent: Wednesday, June 22, 2005 9:47 AM
To: seaint(--nospam--at)seaint.org
Subject: Footing sliding resistance - Friction

Hello Daryl:  I sometime read this list.  Need your
help in understanding your response below.  I think
the area has to do with the resistance also just as a
tire low in area (more surface area) will provide more
resistance that a pressures tire (car wt remain
the same).  What you think?
Tahir
--------------------

Static friction is not dependent on contact area.  For
soils classified as 1, 2, 3 and 4 in '97 UBC Table
18-I-A, friction is the resistance mechanism and it is
independent of the area.

For soils classified as 5 in the same table, cohesion
is the main resistence mechanism and it is dependent
on contact area.

That is my understanding.

John Riley

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