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Re: Capilary tubes.



To change 0.29 to 29 meters (the top of a tree) one must
assume that r=0.5 microns. What evidence do we have for
the existence long tubes of such radii? My guess is that the
"tubes" are not so thin and that they work in tandem, one
after another. Is this correct?
Ludwik Kowalski


In other words the traditional model (the capillary tube
analogy) is not valid here. It is valid for a sponge, or
a tissue paper, but not for a plant. Right?
Ludwik Kowalski

I think so, but I have no practical expertise in this area. It may be that
short plants use capillary action alone.

Here are some references from Life's Matrix by Philip Ball that probably
discuss this in more detail.

1. The Machinery of Life by D. S. Goodsell.
2. Our Molecular Nature by D. S. Goodsell.
3, "Sustained and significant negative water pressure in xylem," W. T.
Pockman et al., Nature volume 378, pp. 715-716 (1995).

I might point out 3 other issues concerning capillary tubes:
1. The subject line in this series is misspelled. The correct spelling is
capillary.
2. Hewitt's Conceptual Physics book (8th edition, p. 228) states,
"Capillary action is essential for plant growth. It brings water to the
roots of plants and carries sap and nourishment to high branches of trees."
So it may lead to the misleading conclusion that water is carried to the
tops of trees by capillary action alone.
3. Capillary action is partially responsible for liquid phase sintering of
materials. According to Introduction to Ceramics by Kingery et at., "for
submicron particle sizes, capillaries with diameters in the range of 0.1
to 1 micron develop pressures in the range of 175 to 1750 psi for silicate
liquids and in the range of 975 to 9750 psi for a metal such as liquid
cobalt."


Dr. Lawrence D. Woolf; Phone: (858)-455-4475; www.sci-ed-ga.org
General Atomics; 3550 General Atomics Court; San Diego CA 92121-1194