[Phys-L] Re: Stopping Distance

[clement at HAL-PC.ORG (John Clement)]

Of course in the simple elementary physics model, the force depends only on
the normal force and mu.  Further, the force should be static friction with
the road so the number of wheels braking should not matter until you reach
the skidding point, at which time it certainly does matter.

But, this does not take into account the point at which the material either
road or tire begins to give way and break down.  There is also the
possibility that the mu is different for truck tires because they must be
fairly durable.

There is another possibility that truck brakes may not be able to produce
enough force.

Incidentally I have been told that motorcycles have a much shorter stopping
distance than cars, so similar factors may be at work here.  Does anyone
have any firm data on this?

There is also the factor of tire tread which also should not matter in the
simple physics model, but Consumer Reports details how stopping distance
varies with tread wear.  I don't think that anyone on this list has yet
explained this latter factor.

John M. Clement

> At 7:00 AM -0500 10/31/05, Eugene Mosca wrote:
> > In yesterday's Parade magazine there was a statement that large
> > trucks require more distance to stop than do light trucks and cars,
> > as much as 50% percent more distance.  Does anyone know the
> > explanation as to why this is?
> >
> > Gene
>
> I imagine that not all forty two wheels may nothave brakes, so the
> share of mass carried by those un-braked wheels doesn't count in the
> friction formula.
> --
>
>
>
> Clarence Bennett
> Oakland University Physics
> Rochester, Michigan
> 248 370 3418
> 248 377 4048