# [Vwdiesel] mileage

Erik Lane eriklane at gmail.com
Sat Nov 28 23:20:46 PST 2009

```> Go ahead with the equations, because we will get a more precise understanding.
> Your effort here would be welcome by most of us, myself included.

This page has a good overview of equations, and is in agreement with
what I have learned.
http://www.csgnetwork.com/stopdistcalc.html

>
> Your comment referred to friction, so I only commented on that.
> That is why I did not discuss intertia, or kinetic energy or other
> concepts.

If you'll look once again at what I said, I specifically talked about
stopping distance and then mentioned the coefficient of friction in
that context.

>
> Speaking of friction...u(k) (kinetic friction) and u(s) (static friction)
> have different cooefficents.  That difference is sometimes called stiction.
> First the static friction must be overcome (getting the big guy on the
> sandpaper moving) and then the kinetic friction must be overcome
> (keeping the sandpaper moving with the big guy on it).  This is typically
> covered in first year college physics, and the first year university
> physics that engineering students take.

Yes, the two are different, but it's not that one has to be overcome
and then the other. The kinetic coefficient of friction is less than
the static coefficient, so once you've overcome the static friction
you already have more than enough force to overcome the kinetic.
That's the reason for ABS - they try to keep right at the edge of the
maximum static friction without breaking free. This provides more
stopping power than when the tires and skidding and you only have
kinetic friction.

>
> The problem of why a lightly loaded truck takes a longer distance to
> stop than a medium loaded truck is an interesting exercise. But it is
> a more complex problem than simple statics.

If you know actual details of that, with equations or other proof, I'd
be interested to hear. So far in my studies, which only involves
second year work, we have both statics and dynamics and they're in
agreement on this.

Thanks,
Erik
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