Re: Automobile tires and friction

[John Barrer <forcejb@YAHOO.COM>]

As the tires heat, they will soften (this is similar
to a glass transition in a non-crystalline polymer).
This probably makes things stickier. But since the
rubber phase of a tire is basically one giant
cross-linked "super molecule", no true melting of the
rubber occurs unless enough bonds are broken thereby
creating molecules which are free to move relative to
one another. John Barrere
--- Rick Tarara <rtarara@SAINTMARYS.EDU> wrote:
> Is this the case for the materials which are used in
> today's tires?
>
> How do skid marks get laid down?  Is the material
> just ripped off the tires?
> How does it then bind with the pavement?
>
> At the race track (drag racing) they lay down layer
> after layer of tire
> material in the burn outs.  Since this is often
> laying 'rubber' over
> 'rubber', how is this done mechanically if there is
> no 'melting' going on?
> [Shots of the track clearly show that the first 100
> m of the track has a
> considerable layer of 'black' material.  I can
> remember as a teenager how a
> friend of mine was so pleased that he got his '55
> Chevy to 'lay down some
> rubber' (on a back road somewhere).  I was never
> able to accomplish this
> with my '60 Nash Rambler ;-( ]
>
> If you watch the races, once the tires start to
> slip, they slip
> dramatically, and the drivers usually can't throttle
> down to regain
> traction.  This can probably be explained by the
> difference between static
> and kinetic friction, but it is so dramatic that it
> also suggests a change
> in the coefficient as well.  Maybe not!
>
> Rick
>
> ----- Original Message -----
> From: "John Barrer" <forcejb@YAHOO.COM>
> To: <PHYS-L@lists.nau.edu>
> Sent: Monday, February 25, 2002 12:05 PM
> Subject: Re: Automobile tires and friction
>
>
> > Tires do not melt when heated (moderately); rather
> > they soften. Vulcanized rubber is a cross-linked
> > structure that cannot "melt" unless some of the
> > cross-links (vulcanization sites) or other
> chemical
> > bonds are broken, so the prospect of a liquid
> rubber
> > layer seems pretty remote. John Barrere
> >
> >
> >
> >
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