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From: gwyn@brl-tgr.ARPA (Doug Gwyn <gwyn>)
Newsgroups: net.physics
Subject: Re: Friction
Message-ID: <2347@brl-tgr.ARPA>
Date: Wed, 23-Oct-85 10:07:05 EDT
Article-I.D.: brl-tgr.2347
Posted: Wed Oct 23 10:07:05 1985
Date-Received: Fri, 25-Oct-85 06:59:45 EDT
References: <956@decwrl.UUCP>
Organization: Ballistic Research Lab
Lines: 21

> It is very much easier to turn the wheel (using the steering wheel) of 
> a moving car than that of a stationary car.  The surface area of tire 
> on the road does not change as it begins to rotate.  The difference in 
> ease of turning, then, is the difference between friction on 
> stationary object and friction on a moving object.  What is the 
> mathematical relation, in this case, between the two frictions?  Can 
> this relation be generalized for other objects?

Sure it can:  It is very much easier to bank a moving airplane than
a stationary one.  The surface area of the airplane does not change
as it begins to bank.  The difference in ease of banking, then, is
the difference between air friction on a stationary object and air
friction on a moving object.

;-)

I mean, if you're going to reason incorrectly about cars, why not
go all the way?

(Note that, unless a car is skidding or spinning its wheels, the
relative speed between the bottom of the tire and the road is 0.)