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Re: [OM] [OT] helmet visors Was Re: framing

Subject: Re: [OM] [OT] helmet visors Was Re: framing
From: davidt@xxxxxxxxxxxxx (David Thatcher)
Date: Sat, 18 Aug 2001 01:35:28 +0930 (CST)
here goes, another one of those noisy argumentative Aussies... :)

very blunt steel dart. contact area maybe 0.1" across = 0.008 sq in. 
terminal spoggy (sorry, sparrow for the non Adelaideans!) 1 to 1-1/2 sq in.

steel dart: 576/.008 = 72,000 eu/sqin
spoggy:                 814 eu/sqin

I think this is the penetrative force used to test the lexan with the
dart. I guess it's the 'ouch, my neck' energy dump value that's a
problem here though!

It reminds me of a story related to me by a friend who hit a sheep on a
'bike at speed on a country road, he likened it to hitting a bag of
water... he managed to keep the 'bike on 2 wheels & stop!  

DavidT
Adelaide, South Australia  

> At 12:26 PM +0200 8/17/01, Jez.Cunningham@xxxxxxxxxx wrote:
> >compare this steel dart and the sparrow.  I kept to "imperial" units 
> >
> >My results are that dropping the 2lb steel dart from 8-10 feet gives 
> >  576  (what are the units?)
> >
> >For the sparrow, say 1 ounce, at terminal velocity of 110mph 
> >(terminal for the sparrow!) the energy comes out at 5162 energy 
> >units!
> >
> >ALMOST TEN TIMES WORSE THAN THE LAB TEST!
> >Sounds to me like you were lucky!  (Not so lucky for the sparrow)
> >Jez-the-ex-mathematician
> 
> I think this ain't right. I get about 161 fps, which squares to
> 26,028, divide by 32 for the difference in mass and you get about
> 814 energy units. If it had been a grackle, though...
> 
> paul   the ex-physicist

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