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RE: Engineering 101 - Was:[ST] New Member



At 01:33 PM 2/5/2004 -0500, you wrote:
>On Thu, 5 Feb 2004, Rich Weyand wrote:
>
> > I think it is simply that the bikes slide on pavement better than
> > people do.  When you hit the pavement, you stick pretty good, as the
> > leather and denim at your contact points with the pavement have pretty
> > good friction.  The bike slides pretty easily once the rubber pieces
> > are off the road, sliding easily both on the pavement and on your
> > clothing, so the bike slows down less and slides right off of you.  
> > At least this is what happened with my low side a couple years back.
>
>To add my non-physics uneducated post, I'd have to guess that mass has
>more to do with why the bike keeps going further than your body does.  You
>may be onto something there with the cordura and kevlar hooking up a
>little though, but I can tell ya' first hand that denim doesn't provide
>any abrasion resistance and will be "gone" before it has a chance to slow
>you down any.  Additionally the pegs and bars digging into the
>pavement should help slow the bike alot making me think mass does have
>alot to do with the why the bike keeps going.  
>
>Physics majors?  Engineers? 

Mmm.  Perhaps I should have noted that I have BS and MS degrees in Physics and taught the college level Physics courses for engineers at Urbana.

When I separated from the ST in my low side, the bike went farther than I did, which is why I noted the friction difference.  While the mass of the bike is higher, giving it more momentum, the normal force on the surface also affects the frictional force.  These are both linear.  So I concluded that the bike had a lower coefficient of friction sliding along on its plastic than I did in heavy jeans and leather jacket.  While the 'sticking out bits' of the pegs, handlebars and may even subtract frictional force.

The basic result that the bike went farther than I did, though, addresses the friction issue on average.  When I hit, I stopped much faster, and the bike slid cleanly off of my leg.


Rich Weyand
1999 Sprint ST "NOT RED"


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