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c.majka@ns.sympatico.ca wrote:
> Hi Jean,
>
> Lots of small (and sometimes not so small) insects and arthropods make
> use of surface tension to move across water.
>
Hi All, Aug 25, 2007
To get some idea of magnitudes I estimated the weight, of a
hypothetical hairy arthropod, that could be supported by pure water at
15o C.
Using approximates of one dyne = 0.001 gram weight, surface tension
of water = 73 dynes/cm and eight legs which each press a brush of 20,
fine, hydrophobic, 0.1 mm-long hairs onto the water, the maximum weight
is about 234 mg; an easy number to remember [20 hairs x 0.1 mm x 2 (each
hair has 2 sides) x 8 legs x 0.1 cm/mm x 73 dynes/cm x 0.001 g
weight/dyne x 1000 mg/g =~ 234 mg].
Taking this one step further, it does not take much surfactant
(natural or artificial) to lower surface tension. So Water Striders and
sparse pond scum may indicate water that is relatively free of surfactants.
It would be interesting to see how much dishwater detergent per dm^2
it would take to sink a Water Strider in otherwise pure water {I would
guess about 0.1 mg].
Yours truly, Dave Webster, Kentville
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