Re: Car acceleration

[Herb Schulz <herbs@INTERACCESS.COM>]

>  > Howdy,
> >  If you think in terms of how the tire deforms as IT pushes BACKWARD
> >  ON THE ROAD  you will see that, indeed, the static friction force
> >  THE ROAD applies ON the TIRE is in the FORWARD DIRECTION.
> >
> >  Good Luck, > Herb Schulz  (herbs@interaccess.com)
>
> Herb Schulz
> I think that you are confusing STATIC friction with
> MOVING friction here. STATIC friction occurs only when the
> car's velocity is zero. In such conditions the friction
> force direction cannot always be determined until after
> a horizontal force is applied to the car. Static friction
> is a kinda hindsight calculation that can be fully measured
> only when it is no longer being applied.
>
> Herb Gottlieb from New York City
> (Where most of our physics textbooks ignore static friction)

Howdy,

No, static friction occurs when there is no RELATIVE motion between
the two surfaces in contact.  Under ordinary circumstances the tire
patch that is in contact with the ground is not sliding over the
ground.  The component of the velocity of the patch parallel to the
road surface as it approaches the ground quickly approaches zero.

Good Luck,
--
Herb Schulz
(herbs@interaccess.com)