Re: Density of snow

[tsm1@domain.elided (Tom Mandera)]

>Density of snow * area of tire * 4 tires.
>
>Won't this just tell you the weight of the snow under all 4 tires?
>Brian Arnett

Man, I've caught some flak over this one, particularly on the Off-Road list!

Basically, the equation is similar to why a ship floats.  An Air Craft
Carrier (and your canoe) float because they weigh less than the water they
displace.  Your boat pushes "down" and "out" on the water, and the water it
pushes away (and thus up on it's own sides a bit) weighs a good deal.

If your boat floats, that water weighs MORE than the "space" taken up by
your boat.  Thus you stay on top.

A submarine purposely gains weight, which allows it to sink.. it weighs MROE
than the water it displaces (and, at some point, they usually set things up
so the sub weighs EXACTLY as much as the water displaced)

On snow, the problem is much more difficult to determine...

Snow isn't a liquid, though it isn't exactly a solid either.. it compresses
like a gas, until it becomes a solid (ice).  I don't believe, in most cases,
the snow on the sides of the "depression" "push" up on the object in the
depression, so we're left with just the "bottom" of the depression.

When you drive over the snow, you are displacing a certain amount of snow as
your tire sinks.  However, in snow, it's not quite "displacing" but usually
more like "compressing" until you make ICE (or hard pack snow) under the
tires, making things uncompressible.

The problem is to figure out what your "foot print" is, and then determine
how much weight that first inch of snow depth would support.. and then the
second inch, the third inch, etc.

The problem is the different snow-pack types, and that, as your truck sinks
farther down into the snow, it compresses the snow more, resulting in more
"strength".

At the same time, we need to take into consideration the fact that snow is
self-compressing.  As snow falls, it's own weight compresses it somewhat,
more so towards the bottom.

So, as we compress the snow downwards, we're also compressing into more
solid-like snow.. 

I guess the easiest way for me to figure this out is to just grab a 2x6,
weigh it, then place it on some snow and start adding weights.. 

Trying to calculate a number is getting WAY too complicated.. I must not 've
been thinking very well yesterday when this idea got started in my head..
(thinkin' too much about getting my Scout back!)

Once I figure out how much static weight the snow will support, we add in
another variable.. as your truck is MOVING, it "weighs" less.. it doesn't
stay in one place long enough to fully compress the snow.. ever "bounce"
very lightly over someone's foot / back while laying on the floor? (this was
one of those tricks my father used to do.. walk right over yer tummy, but
almost NO pressure).  Just take that and apply it to a truck rolling
smoothly over the snow.. just don't stop!

What an ugly mess I've started thinking about.. yikes!

*sigh* What have I started? ;)

-Tom Mandera, Helena MT
http://www.tmcom.com/~tsm1/scout
'72 and '77 Scout IIs