Re: car tire friction & contact area

[Rick Tarara <rtarara@SAINTMARYS.EDU>]

As you will see from the responses, this can get pretty complicated with
nobody really knowing exactly the answers.  However....to keep it
simple--concentrate on the rear tires of a drag racer.

1)  Here the width is more about heat dissipation than friction because the
mu for a rubber, liquid rubber, and asphalt interface is really low!  In
fact,  watch what happens when they spin up the tires--they get higher and
more narrow!

2)  The 'burn out' intentionally melts some tire material over the area from
which the car starts.  Turns out that mu between 'rubber' and 'rubber' is
higher than between asphalt and rubber.

There will be more complete and complex answers--but the above is
approximately true (I think).

Rick

*********************************************************
Richard W. Tarara
Professor of Physics
Saint Mary's College
Notre Dame, Indiana
rtarara@saintmarys.edu
********************************************************
Free Physics Educational Software (Win & Mac)
NEW: International Energy Project
               energy management simulator
           SIMLAB-Pendulum lab simulation
www.saintmarys.edu/~rtarara/software.html
Energy 2100--class project
www.saintmarys.edu/~rtarara/ENERGY_PROJECT/ENERGY2100.htm
********************************************************


----- Original Message -----
From: "GJ Schade" <gjschade@HOTMAIL.COM>
To: <PHYS-L@lists.nau.edu>
Sent: Monday, April 19, 2004 1:17 PM
Subject: car tire friction & contact area


> I did an archive search on this topic and only found somewhat vague
answers,
> so let me try to get the discussion going again.
>
> We learn in my high school physics classes that the amount of area in
> contact between two surfaces does not affect the amount of sliding
friction
> between them.  Invariably, every year a student asks why are wider car
tires
> better at handling, etc.  I respond, somewhat vaguely, that the tire is
> rolling over the road with little or hopefully zero slippage, and
therefore
> it is a different phenomenon.  One student this year, showed me a car
> enthusiast listserv thread on the same topic.  One posting stated that Ff
=
> mu * Fn only applies experimentally if mu < 1 and rubber versus road has a
> mu > 1.  Is that really the case?  Does anyone have a high-school level
> explanation for wider car tires that I can pass on to my students?
>
> I copied and pasted the address for the car enthusiast listserv thread
> below.
>
> Greg Schade
> Physics/Chemistry Teacher
> Parkway West HS
> St. Louis, MO
http://www.team-integra.net/forum/display_topic_threads.asp?ForumID=10&TopicID=76204&SearchPagePosition=1&search=rubber+coefficient&searchMode=allwords&searchIn=Thread&forum=0&searchSort=dateDESC&ReturnPage=Search
> _________________________________________________________________
> Check out MSN PC Safety & Security to help ensure your PC is protected and
> safe. http://specials.msn.com/msn/security.asp