Re: Doucet effect....
>The increase in pressure differential due to growth
of
>the cavity exceeding the rate of air permeation into
>the cavity is still on the table.
>I'm believe changes in barometric pressure would may
>little difference because they are so small. Flying
>the pumpkin from sea level to 10,000 feet would have
a
>significant effect, however, if my theory holds
water.
The differential pressure from atmospheric sea level
to the inside of a pressurized aircraft is more than
from sea level to 10,000 ft. Ray Waterman , Bill
Bobier, who ever sent one to China and any others who
have shipped a pumpkin via Aircraft- did any of the
pumpkins split in flight ? I haven't heard of this
happening to any of them.
I don't think pumpkin skin is air permeable… but I
don't know. and i'm sure someone could run an
experiment and find this out. I tend to agree more
with Rocky. That the pumpkins produce their own air
as the grow- that is comes from the inside. I would
think that the stem would be more air permeable than
the skin. If the pressure differential were that big
of a factor then like I said before one would hear a
"whoosh" , even if it was small, when one cut into a
pumpkin. The smaller the cut the bigger the whoosh.
So if you pushed a small diameter metal rod all the
way through then pulled it out one would expect to
hear some sound. I hope someone tries this experiment
when they cut their pumpkin open. Personally I don't
think there will be any, that there is not pressure
differential between the inside and out side.
To expand on my previous post:
I think the major cause of dill rings and splits is
because of the weight of the pumpkin on the top of the
pumpkin that is transfered down to the sides and
bottom into an area where there is a defect. And
defects are caused naturally by rapid growth & other
factor and unnaturally factors- dents- scratches etc.
That this defect spot can't handle the load so the
pumpkin fails there. Shape is an important factor.
Generally pumpkins that are long have them and
pumpkins that are short don't. They usually happen
toward the blossom end where the pumpkin is thinner.
I think they just crack under their own weight because
of the longer unsupported span. Shorter pumpkins
don't have as much unsupported wall on top so they
don't get that added stress and don't dill. Taller
rounder pumpkins have more of a arch shape which is
structurally stronger. Kind of like a egg is hard to
break if you just push on the ends- because of it's
shape. But is a lot easier to break if you push on it
from the sides. I think another major contributing
factor is defect is the pumpkin walls. We all have
seen defect on the skin… hard or soft spots that
naturally occur… I think that there are defect inside
as well.. That is just the way they grow. Some of the
skin defect might go through to the inside also.
Anyway- these are structurally weak points in the
pumpkin - like knots in wood.
If you take a beam or plate in bending the top is in
compression and the bottom is in tension.
A 2x4 supported at each end with a weight in the
middle- is the classic example. If you have a 2x4
with a big knot right in the middle it will break at a
much lower weight than one that doesn't.
Most things including pumpkin have a higher strength
in compression- which mean in simple terms if you push
on them they are stronger than if you pull on them.
The top of a longer pumpkin is like the 2x4… The skin,
which is stronger anyway, is on top and is in
compression. The bottom of the top wall which is just
flesh, which is weaker, is in tension… so it fails
until the load is carried but the remaining stronger
skin. It would be like gluing a piece of stryofoam to
the bottom of our example 2x4 then putting weight on
it till the stryofoam cracked… but the wood didn't.
That's what I think dill rings are. I think most
splits are cause by defects either on the inside or
outside of both, due to rapid growth and that as the
weight of the pumpkin increases they just fail. Like
the 2x4 with the knot. And the key in failure is not
the over all force but the stress. Pound per square
inch. You can have a force of a million pounds but if
you spread it over a million square inches then the
stress in 1 PSI, (pound per square inch). But if you
take a million pounds and only spread in over 1 square
inch then the stress is a 1,000,000 PSI. It's why
nails are pointed and have a bigger flat head. Ever
try to pound in a nail backward ? the force is the
same in each case the stress is not. When you pound
in a nail the right way all that force is concentrated
at a small area on the tip of the nail - which is
enough to fail the wood locally and the nail drive in.
I really just gave a basic overview of simple
engineering principles. I could get more in depth if
people wanted .. but I don't want to ramble on and on.
So…don't even get me going... bending stress, shear
stress, thermal stress all combining at once.
Diana that I figure you already know a lot of what I
mentioned -but I want to try to explain it so others
could follow also. So don't think I was talking down
to you because I wasn't. I think the best way in this
game to have your name attached to something it so
grow a big one or have one which seeds grow big ones.
Also I never tried an electric blanket, just thought
of it. Where i grow it is not feasable. I think it
might also be hard to reglulate the temperature
throughout the day and night. And personally i don't
think it would make a difference. ... that it why i
shared it. I've got lots of other good ones that i'm
not sharing !!! :)
One last note that relates to the upside down posts:
if the stem wasn't a potential problem. i.e.- weak
spot. I think the ideal way to grow a pumpkin would
be on its stem. They would be stronger structurally
because the thicker shoulder part of the pumpkin is on
the bottom.
Gordon Tanner
Maple Valley WA
geek boeing airplane engineer
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