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Re: Friction

Having driven on ice and snow, particularly in northern Minnesota, for
the last 40 years and having only recently purchased a vehicle with a
four wheel anti lock braking system I can testify from personal
experience and deliberate testing that the ABS systems do both-they allow
one to maintain greater control and they stop one faster (under all but
some very special conditions).

The faster stops are due to the fact that static friction is greater than
sliding friction. The greater control is because under conditions of static
friction the front tires experience a greater lateral force than frontal
force (an awkward expression of my own invention which is best
explained with a diagram but my mail system is not capable of such) while
they are still rolling. Thus the driver can control the
direction of the frictional force on the auto by turning the wheels.
When the wheels are locked and sliding the frictional force is simply in
the direction opposite to the motion of the tires relatively independant
of which way they are turned.

(After re-reading the above paragraph I am not sure I got my point
across. I do maintain though that faster stops and greater control are
gained with ABS.)

Jim Riley, Department of Physics
Drury College, Springfield MO 65802
e-mail: jriley@lib.drury.edu
(417) 873-7233

On Mon, 15 Jul 1996, Paul Camp wrote:





As I understand it, antilock brakes are not intended to make you stop
sooner. In fact, I believe the reverse is true. The point is so that
you can maintain control of your car. You would like, whenever you do
stop, to do so at a location of your choosing and not simply because
you hit something a great deal larger than you.

Paul J. Camp "The Beauty of the Universe
Assistant Professor of Physics consists not only of unity
Coastal Carolina University in variety but also of
Conway, SC 29526 variety in unity.
pjcamp@csd1.coastal.edu --Umberto Eco
pjcamp@worldnet.att.org The Name of the Rose
(803)349-2227
fax: (803)349-2926