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Message from discussion Doubleplusgood - first impressions
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Andrew McKenna  
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 More options Feb 19 2007, 3:48 pm
Newsgroups: aus.motorcycles
From: Andrew McKenna <NOcmorSPAM3...@NObigpond.SPAMnet.au>
Date: Mon, 19 Feb 2007 04:48:14 GMT
Local: Mon, Feb 19 2007 3:48 pm
Subject: Re: Doubleplusgood - first impressions
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Iain Chalmers wrote:
>> Watch out for lightning strike!

>> --
>> Cheers

>> Andrew

>> (Make a lightning rod by gluing a blunt ferrous rod to the top of the
>> motorcycle helmet, attaching a 4 metre length of copper strap to the rod
>> with copper wire, and attaching a suitable boat anchor to the free end
>> of the strap to make sure it stays earthed - any Windows 98 computer
>> would do.)

> A _blunt_ rod? Have you been taking physics lessons from Hamish again?

> big

"     Calculations of the relative strengths of the electric fields
above similarly exposed sharp and blunt rods show that although the
fields, prior to any emissions, are much stronger at the tip of a sharp
rod, they decrease more rapidly with distance. As a result, at a few
centimeters above the tip of a 20-mm-diameter blunt rod, the strength of
the field is greater than that over an otherwise similar, sharper rod at
the same height. Since the field strength at the tip of a sharpened rod
tends to be limited by the easy formation of ions in the surrounding
air, the field strengths over blunt rods can be much stronger than those
at distances greater than 1 cm over sharper ones.
     The results of this study suggest that moderately blunt metal rods
(with tip height–to–tip radius of curvature ratios of about 680:1) are
better lightning strike receptors than are sharper rods or very blunt
ones. "

C. B. Moore, William Rison, James Mathis, and Graydon Aulich, "Lightning
Rod Improvement Studies". Journal of Applied Meteorology: Vol. 39, No.
5, pp. 593–609. Langmuir Laboratory for Atmospheric Research, New Mexico
Institute of Mining and Technology, Socorro, New Mexico. April 10, 1999.

Extracted from that authoritative source Wikipedia:
http://en.wikipedia.org/wiki/Lightning_rod

--
Cheers

Andrew


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