rec.autos.simulators

Lets do a little experiment shall we? <G>......

Put your palm down on a table and push on it. It resists breaking
'traction', but when it starts to slide it slides quite easily.

Another example is to go move your couch or refrigerator. Once your get it
moving it requires less effort to keep it moving, once it stops it requires
considerably more force/energy to start it moving again. NOTE: This has very
little to do with momentum, so don't assume anything like that. Kinetic &
potential energies are an entirely seperate subject.

Got it? Sliding friction is always less that static friction.

Sliding friction can be beneficial to a racer in many ways tho. A great
illustration is a good Rally driver who slides the back end around in a
corner to achieve a higher/quicker angle of rotation in a situation where
apex speed & exit speed is less important than rotaional speed. They are
able to start accelerating before they would be able to if they had just
driven the corner 'at the edge of traction' like a typical road racer does.
The situation & of course many other variables dictate the proper technique
for a particular corner.

Being a good racer requires an excellent understanding of phsyics IMO.

"Never pat a burning dog~!!!"

In General you are correct.  Being I deal with everyday in Pneumatics
cylinders I had to design a cylinder that the static and dynamic frictions
were as close as possible.  It can be done, but requires some special
stuff.

For cars tho static and dynamic frictions will always be different values.

Dave

: Lets do a little experiment shall we? <G>......

: Put your palm down on a table and push on it. It resists breaking
: 'traction', but when it starts to slide it slides quite easily.

  Poor experiment - it is wholly subjective - maybe it slides quite
easily because you're not applying the same force?  How can you tell
"sliding easily" from "just sliding" (if I push my hand slowly enough it
seems to be "just sliding" to me).  If sliding friction is much less
and you apply "the same force" then your hand would continue to
accelerate - didn't notice mine doing that.  :-)

: Got it? Sliding friction is always less that static friction.

  I'm not sure if this general conclusion is correct.  Certainly I'm
willing to believe it is the case in racing situations and for a large
variety of cases it is correct.  I'm pretty sure, however, that we can
find substances where sliding friction is greater.  

  I posted an experiment about static/sliding friction on
rec.autos.sports.f1.moderated this week which you might still be able to
find describing an experiment using a ***ised mousemat a "pulley" and
a weight showing that, for a *** mousemat at least, sliding friction
actually is pretty similar to static friction.

  In brief: use paperclips and cotton to fasten the mousemat to a
weight - use a pulley or some kind of roller to hang the weight over the
side of the desk.  Load the mousemat with "downforce" (small weights)
until there is just enough weight to stop it sliding.  Give the mousemat
a shove.  If the mousemat accelerates off the desk then the sliding
friction was much less.  My experience was that the mousemat would slow
down and either continue to move very slowly or stop.  Meaning that, in
that case, the sliding friction wasn't much lower (if any) than the
static friction.

--
Richard G. Clegg     Only the mind is waving
Dept. of Mathematics (Network Control group) Uni. of York.

www: http://www.racesimcentral.net/

Yes, standing on the brakes is the natural reaction. Unfortunately, it often
leads to sliding straight into an oncoming truck, a moose, a tree or something
else that will certainly spoil your day. Generally, ppl panic brake (yup,
that's the term - panic being BAD while driving) when they find themselves
headed straight towards such an object. Thus, pumping the brakes and getting
just a little steering (I really don't think most ppl can do modulated
breaking efficiently in a crise situation) will be a better idea than locking
them up. Whether or not you get the speed down as much as you possibly can is
irrelevant when you don't hit...

I have tried pump braking for real several times and it works. I have also
tried locking up the brakes both when playing around and on a skid course
(mandatory in driver training here). You do stop, of course, but you will not
avoid any obstacles.

Add to that the fact that most cars have the largest crash zones towards the
front and most passenger safety devices are built to take up acceleration
towards the front. With pump braking, the car tends to maintain it's
direction. With locked brakes, it will spin like a top and chance will deside
which direction it will hit.

Add to THAT the natural reaction many people have when the car starts to spin.
They release the brake and the car goes off to the side it happens to be
pointing at that moment, again quite possibly hitting something or someone.
Allowing people to follow their natural instincts in an unnatural situation
(driving a car) isn't the thing I would do...

Oh yeah, and most ppl will not need this before the braking distance is way
too short anyway so they'd probably be better off steering around or into the
ditch in the first place.

I agree with my driving instructors here. Locking up probably is the worst
thing to do, short of stepping on the accelerator (as many ppl will do when
they panic and mash both feet down). Much better to have pump braking embedded
somewhere in the spinal cord of all drivers.

My $.02,
   /ft

P.S. I read somewhere that in most car crashes, the driver only hits the
brakes AFTER impact anyway...

/Chrille

/Chrille

I've heard real race car drivers are more often involved in traffic
accidents than non race car drivers. If it's true it could be because race
car drivers need more speed to get day to day driving interesting... Then
again if you see the day to day driving as some kind of endurance race where
the oldest driver alive is the winner, you might use your simulator
experience to your advantage. Follow traffic rythm, dont upset the other
drivers, be aware of anything that moves or could be moving soon. Then again
I could be very tired from working the whole week...

/Chrille

The reason a racing tire breakes the Newton laws is because at a certain
temperature interval it gets sticky. Place your hand on such a tire and you
will have trouble removing it - I shit you not :o) (loved that expression in
the movie "The Rock" :o)). So the larger contact area, the more glue effect.
The glue effect dont care one bit about what the pressure per area is.

/Chrille, and that's my principles, if you dont like them, I have others ;o)

A common problem is not to get into the pedal from the MOMENT braking is
needed. I usually find it safer in a semi-emergency to brake at the
threshold of adhesion from the moment I see the need to brake, and then tail
off the braking if the situation subsides.

Ryan

Sim racing is far more enjoyable when you take it seriously,  and it's
too easy not to take it seriously.  I think what's needed is a sim racing
"reality chair",  that has a spring loaded baseball bat that snaps around
and smacks you in the ribs when ever you***up. It would add a little
intensity to the driving.
--
Don Scurlock
Vancouver,B.C.

     /ft, funspoiler who swerves for mooses, children and not much else

(Yup, I once had the horrible experience of having a kid jump out from behind
a parked car... Luckily i was doing 30 km/h at the time and could brake/steer
around, but I did not feel like driving for weeks and months afterwards... And
you'll find me the slowest driver ever when there are parked cars or other
view obscuring objects along the road. Please try to out-slow me, everyone!)