From: carl@montebello.ecom.unimelb.EDU.AU (Carl Brewer)
Subject: Re: When you're wrong, you're wrong. (was Re: ABS ???????)
Summary: Minor nitpicking
Organization: Dept. Engineering Computer Resources, Melbourne Uni.
Date: Mon, 9 Nov 1992 22:51:33 GMT

In article <1992Nov9.185354.1@economics.adelaide.edu.au> ecrjbruce@economics.adelaide.edu.au writes:
>                              
>Not only have I read my info in 2 texts, it's backed up by a group of friends.
>That may not mean much to you except that one is doing a PhD in Physics, 
>another in Maths Sciences, the third in Engineering and the fourth is a 
>qualified engineer who goes racing.  The other sources I referred to are a CAMS
>(confederation of Aust. Motorsport) handbook for drivers and my lecture
>material from an advanced driving course I did about 2 years ago.

hmmm, you trust CAMS to be accurate?   :)

>
>> 
>> Well I don't know what kind of physics they teach in Oz.
>> 
>> You also insist that dynamic friction occurs when the wheel is rolling freely. 
>> (dynamically I guess!) 
>
>Thats what I have been told.  Thats what is in various handbooks.  As for being
>read in texts that refers to the fact that dynamic friction takes much greater
>force to break traction than static.

simple physics lesson "FRICTION":

static friction is defined as the force resisting sliding motion between
two surfaces that are in contact and not sliding against each other.  eg:
your car tyres when the car is staionary, and the wheels are stationary, or
when the car is moving, and the wheels are moving and there is no slipping.

Dynamic Friction is defined as the force resisting sliding motion between
two surfaces that are *not* stationary reletave to each other, eg:
your tyres when the car is stationary, and the wheels are spinning, or when
the car is moving, and the wheels are locked.

static friction is *always* greater than dynamic friction

hoiwever, a misunderstanding can occur when refering to brakes,
because as long as the wheels are turning, the brakes will be in
dynamioc friction, not static.  The only time the brake pads/rotors/drums
are in static friction is when the wheels are locked.

I hope this helps calm things down a little


>You claim that I fail to understand basics yet you claim that the greatest
>advantage ABS has is on dry tarmac - which is precisely ABS has it's LEAST
>advantage over a human driver.  ABS excels in difficult conditions, the gap is
>much closer in good conditions.  To me that's a basic principle of ABS.  Of
>course you no doubt think I am wrong again.

ABS excels in wet bitumen, but in really adverse contidtions (snow, ice,
gravel) ABS is much worse than humans.  (nitpick, but hey ..  :) )
 
>Well as I have said, from the way I see it the evidence is stacked against your
>argument.  You may disagree (that's your right after all) but I have
>several opinions and several sources which disagree with you.  On probability I
>would say that suggests I am more likely to be correct.  Again I say to you,
>show me where I am wrong and provide substantial evidence to prove it.  I have
>my opinions and have checked them reasonably well (I can't be bothered to get
>more opinions to be honest) but if you can show me exactly how I am wrong then
>let me know.

seems to me like a misunderstanding, more than anything else.

>Sure you can have both at the same time - in PRACTICE.  Read what I sent to you
>about rally turns etc.  Maybe you didn't interpret it quite properly.

ohh, what's this about rallies?  :)

>>
>Maybe we had better define slip, that may be the root of all the hassles.  As
>for human drivers being able to maintain perfect human braking and 10% slip etc
>then tell that to Gerhard Berger.  I was sitting at the end of the main
>straight and he didn't seem to do it 100% of the time.  Situations like that
>are where ABS (or EBS - see my post to you about susension being an important
>parameter) come in really handy, they save your tyres from damage (flatspots)
>and give you a greater margin of error with regard to control etc.
>
>** Are you defining slip as the slip between pads and rotor??  If so we may 
>have a cause of the problem here, we talk about slip as being between the tyre
>and the surface.  If you are working on the former defn than it would explain
>much. Sorry I didn't mention it earlier it only just occurred to me that we may
>have had problems with definitions of this sort **

ahha, the crux of the problem rears its head at last :)


-- 
 Annal  Natrach, Usthvah Spethed,         carl@ecr.mu.oz.au (IRC: Bleve)
 Dochoel Dienve                           carl@munagin.ee.mu.oz.au
					  carl@montebello.ecom.unimelb.EDU.AU
 Merlin, where are you?  Call your dragon, to weave a mist...