Rolling friction assumes a single, 1 dimensional point of contact. This is not reality, but, it can approximate reality if proper judgement is used. The reality that most closely matches it is a railroad car (ie, metal wheel on a metal rail). No real text book would discuss rolling friction without noting its limitations.

In reality, tire companies and racers use friction coefficients much greater than 1 based on emperical studies.

--Outlaw.

what i think now is that nowadays racing tyres have so much difference between dynamict and static coeficients of friction that drive gripping is an advantage over sliding

but i recall mentioned times when sliding was an advantage

i can see why by dynamic friction increasing with speed

probably in this old components dinamic and static coeficients were close

Perhaps that is the problem with the parachutist, insufficient static coeficients of friction.

It is possible that could be improved with buttered toast.

Interesting?

So your saying you belive the coefficient of friction of tires has changed over your lifetime?

And that somehow your existence on this planet has affected the coefficient of friction of tires?

Hmmmmm

You may be onto something there?

Because looking at your picture, I think if you were to plot the number of hairs on your head for each year of your life

THAN TAKE THE INVERSE OF THAT GRAPH

And than plot the coefficient of friction of tires for each year of your life

I predict that they will be trending in the same direction!

At which point I think you could make the argument that your existence on this planet has in some way affected the coefficient of friction of tires over your life time!

Not sure about that but googling parachutes and motor vehicles I did find this:

http://anticipatethis.wordpress.com/...d-what-no-186/

http://anticipatethis.files.wordpres...hute.png?w=720

Warning do not try this at home.

Interestingly most discussions on parachutes discuss Lift not friction.

well, butter does help to reduce friction, in some circumstances :cool:

HAHah! I nearly did this. I can tell you he wouldn't be on the bike for long. I had an old helmit and the padding had died long ago, so there was a gap between me and the helmit. So open stretch of road, open the throttle, 130mph with my head down. The helmit slipped down a little slightly obscuring my view so I tilted my head back... It was like a giant was trying to pick me up by my head! It nearly ripped me off my bike by the chin strap... :-P

god almighty, is this insanity really still going?!

Guys don't you realise you're doing this man only a great deal of harm by indulging him? :confused:

but stern you said i was not crazy that i was just a weirdo

now you imply i am

maybe youre just acting with a convenient role according the circumstances?

I am not implying anything here, I just can't understand your attitude, if I were you I would be ashamed of talking physics, since you demonstrate your understanding is limited and based on wrong assumptions to say the least (the signs of a creative but lazy student). I mean, do you really like making a fool out of yourself? And don't say that you're a genius or that other people became famous because they questioned the reality as we know it: Albert Einstein was a genius because he had a thorough understanding of physics, not just because he was creative.