# [Vwdiesel] mileage

Val Christian val at mongo.mongobird.com
Sat Nov 28 19:10:26 PST 2009

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> You're right, it's elementary. You completely forgot about inertia.
> The frictional force increase is directly in proportion to the
> increase in weight, but the inertia is also a direct proportion. The
> feather takes almost nothing to stop, while the heavy person takes a
> *lot* to stop. The equations for the distance that something will
> travel don't have weight in them, because it cancels out. (Well,
> actually mass, but since we're doing all of this on Earth, that's not
> an important distinction.)
>
> If you want to play this game some more I can go find equations to back it =
> up.
>

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.

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.

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.

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.

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