My error. My comment applies to a "slide to stop" situation where the
wheels lock up. When a vehicle slides to a stop under the conditions
cited above, the weight is irrelevant.
Source? Google J. Stannard Baker, Professional Engineer, founder of
what was known as The Traffic Institute at Northwestern University.
He's basically the "father" of crash investigation.
As I recall, the downward force created by the weight of the vehicle
balances out the lighter weight of the second vehicle by increasing the
effectiveness (for want of a better word) of the coefficient of
friction. That's why you don't see the weight listed in that particular
Lotsa strange stuff happens when wheels lock up. Loss of control, cars
wind up bass ackwards.
Find yourself a vacant level, parking lot with a bit of rain to liven
things up. Drive in a straight line at 25 -30 m/h and without touching
the brake pedal, pull up hard on the parking brake (locking the rear
wheels) and tell us what you see. Hint: You'll find yourself looking
at where you've been rather than where you are headed<g>
On Friday, July 11, 2014 9:42:42 PM UTC-4, Unquestionably Confused wrote:
I see your point and agree that it makes sense that the more weight,
the greater the stopping friction should be. I still question whether
it will exactly cancel the effect of the increased momentum. For example,
I would wonder if when a tire is locked, skidding, getting super hot,
there isn't some limit beyond which additional downward force doesn't do
much good. I googled a bit to see if there was some actual real world
testing done, but I didn't find anything. I'm sure there must be some
testing out there that was done. Would be interesting to see.
The above approximate model presumes normal static friction force which
is proportional to normal force (weight). Since momentum/energy are
proportional to m also, they cancel under that assumption.
The problem is,
"In theory there is no difference between theory and practice. In
practice there is." -- Jan L. A. van de Snepscheut
It's an extremely limited theory for a very complex problem.
As for research there's actually quite a lot -- one of the more
interesting pieces I saw is at
On Fri, 11 Jul 2014 19:30:48 -0500, Unquestionably Confused wrote:
You know nothing about real life.
"Top Gear" did a demo of this. With just the driver, the car stopped as
Add 3 passengers who all weighed over 300 pounds, it took another 100 feet
Having been a professional truck driver, it takes much longer to stop a
loaded tuck. At 70mph and fully loaded, even longer.
My brother-in-law took one of those courses for a trucker's license. He
dropped out when he realized the class was a scam and that the graduates
were unfit to drive those big rigs. He said that the situation was quite
scary and that it's not safe on the highways with these drivers out there.
Luckily, we don't have those giant trucks in this state.
My brother-in-law is a nut for safety. He once was on a job site where
they were pouring concrete for a building. He told the foreman that they
were not waiting long enough between pours before going to the next
level up and that it was unsafe. As I recall, the wet weather messed up
the cure times. He quit because he was ignored. A short time later the
whole thing collapsed, killing a lot of people. Sometimes they show the
video of this on TV. That guy was always kind of a troublemaker but
sometimes that's not a bad thing.
That was the number we used as a baseline for training in ideal
conditions in a modern rig. The thing is how many times do you try to
leave yourself open braking room only to have 10- 4 wheelers drop into
the hole? I know I could never open a hole in most places with traffic,
So you do the next best thing, look for ways to slow down and try to
leave yourself a way out.
Oh that's funny.
You asked what the skirting on the side of trucks was for.
I answered after a 10 second google search.
You claimed it was illegal to carry a firearm in a commercial vehicle.
I proved otherwise.
Maybe you drove trucks, but it's obvious you were fired for
To reply via e-mail, remove The Obvious and .invalid from my e-mail address.
On Fri, 11 Jul 2014 12:33:01 -0700, Ann Marie Brest
I can't say how long it takes to stop without knowing the weight of
the truck, what kind of brakes, what pavement condition, etc. However,
if the driver, by operating an overloaded vehicle at too high a speed
with inadequate brakes, and following too closely to allow a safe
stopping distance can be considered to be driving carelessly - which
can easily be argued, it IS a criminal offence.
If someone died from his carelessnes it is arguably vehicular
manslaughter - or at the very least careless driving causing death. I
believe both of these (at least in Canada - don't know about
California) are criminal code violations.
I would not want to be in the driver's shoes trying to fight the
charge in court.
On 7/11/14 10:34 PM, firstname.lastname@example.org wrote:
The weight of the truck doesn't matter for the stopping distance.
No. In California, there's negligent operation, which is a violation of
the vehicle code and reckless driving, which is in the penal code.
No. In California, if you're committing an unlawful but non-felony act
while driving and you kill someone, then you may be charged with
vehicular manslaughter if you acted negligently. Ordinary negligence
will get you charged with a misdemeanor; gross negligence may get you
charged with a felony.
(If your unlawful act was a felony, you could be charged with felony
It's impossible to say whether your claim is true that a criminal
offense is "easily argued." The driver must have been negligent, i.e.,
he must have acted recklessly and either knew or should have known he
was doing so.
On Fri, 11 Jul 2014 19:30:48 -0500, Unquestionably Confused
Tell that to a proffessional truck driver. The difference in load,
brake swept area (number of brakes/tires) will both affect stopping
It takes just as much horsepower to accellerate a load from a stop to
60MPH up a hill in a given time or distance as it does to slow the
truck from 60MPH to a stop down the same hill. If you double the
weight, it will take a lot more time/distance or a lot more horsepower
to accellerate the load up the hill - and the same amount more
horsepower to stop the truck. That horsepower is absorbed by the
brakes when slowing the load, turning it all to heat. The more brakes,
the more friction area, and the better the heat dissipation, all else
being the same. The hotter the brakes get, the less braking force they
can exert due to thermal brake fade (a complete discussion topic on
Now the size and number of tires on those braked axles also makes a
difference, because if the brakes run out of friction before the
tires, the brakes limit the stopping distance. If the tires run out of
traction before the brakes, the tires slide. The coefficient of
friction of a hot tire sliding on asphalt is significantly different
than the coefficient of friction between a warm rolling tire of the
same size and the same asphalt. That is a large part of the reason for
antilock brakes. Tires braked at the limit of adhesion stop a LOT
faster (and with more control) than a sliding locked tire. This is
true of almost any road surface.
Now, If the truck has more than adequate brakes, and more than
adequate tire for the job, the difference in weight won't matter much.
If on the other hand the truck has adequate tires and brakes to handle
stopping 40 tons from 60MPH to a dead stop in 600 feet on a 6% grade,
he is NOT going to stop 60 tons in the same distance on the same
grade, just as it will not stop 40 tons in the same distance on a 12%
The question if it is criminal if he cannot get stopped hinges on
Was the truck loaded within it's GVW rating? If it was overloaded, the
driver is on thin ice.
Was the driver driving within the posted speed limit? If not, again,
he is on thin ice.
Was the truck in sound mechanical condition? If not both the driver
and owner are now in trouble.
Were the air brakes in adjustment, and was the brake check logged in
the log book? If not, again the driver is on thin ice.
If the question of whether a prudent driver would have approached that
hill at the speed he approached it -even if it was within the speed
limit is no, the driver is on thin ice.
It appears limitted driving experience was a major factor in the
accident. Unfamiliarity with the road may also have contributed - but
if any of the above questions get a "no" answer - - - - .
"Sometimes when you are on thin ice you end up in hot water".
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