[Vwdiesel] mileage

Val Christian val at mongo.mongobird.com
Sat Nov 28 17:26:54 PST 2009

```Apparently the physics classes didn't work.

Assume that you have a human sized sheet of sandpaper.  Put a feather on
the sandpaper sheet and try to pull it.  No problem, just a little
resistance, as you scuff the finish on the wood floor.

Now on that human sized sheet of sandpaper, put the biggest, meanest
and heaviest person you can think of.  Now pull it.  Can't move it?

That's the physics part.

F(f) = uN, where N is the normal force.  Weight and N work together,
and the big guy on the sandpaper increases the N.  Therefore the
frictional force increases linearly with an increase on the weight
(hence the normal force).

Seriously, you took university physics in college, and engineering
courses?  Sorry I'm being hard, but it's pretty elementary.

>
> I still find it a little counter-intuitive, but in both my engineering
> and physics studies it's been drummed into us that the single real
> factor with stopping distance is the coefficient of friction at the
> point(s) of contact.
>
> Therefore only the two materials in contact, not the amount of weight
> on them, nor the amount of road contact area.
>
> I don't think it holds exactly, because of factors like heating of the
> tires and therefore changing the coefficient, but it should still stay
> relatively close to the same. (This is assuming that what they are
> teaching us is correct. I'm assuming so.)
>
> At the very least I think it is a little foolish to assume that a semi
> truck, or anything else for that matter, can't stop quickly. Sure,
> there are lots of vehicles that have low power and slow acceleration,
> but anything that locks up all of its brakes is going to be stopping
> pretty quick.
>
> Erik
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>

```