Re: [RQ-Rules] Whoops

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From: Stephen Posey (slposey@concentric.net)
Date: Tue 05 Feb 2002 - 19:31:53 EET

Peter Maranci wrote:
>
> Whoops, I forgot to say: voting on the Die-Roller's list is slightly
> counter-intuitive. "1" is worst and "5" is best. Go figure.
>
> Here's a RQ question, while I'm at it: has anyone done any sorts of
> calculations about the weights of metals? I made a magic item that's a
> metal tube about ten feet long with a four foot diameter, of unknown
> metal and thickness. I estimated its weight at 3,000 lbs, but now am
> wondering...that sounds sort of low.

<putting on my math teacher hat>
That rather depends on which metal it's made of. Here's how to figure
that:

1) Your item has a radius of 2 feet
2) Your item has a length of 10 feet
3) The formula for the volume of a cylinder is pi * (radius * radius) *
length

Therefore your item has a volume of
      pi * 2 * 2 * 10
  = pi * 40
 ~= 3.14 * 40
  = 125.6 cubic feet

Now, for example aluminum weighs about 170 lbs per cubic foot, so
assuming the cylinder is solid and of homogeneous construction it would
weigh about 5,024 pounds.

Aluminum is one of the lightest metals, so you're correct that 3,000 lbs
is very light for this construction (given the assumptions above).

Here's a few other common metals for comparison's sake:

Material Weight of Weight of cylinder
            material (lbs)
            (lbs/cu ft)
============================================
Brass 525 65,940
Copper 550 69,080
Gold 1,204 151,222
Lead 711 89,301
Silver 655 82,268
Steel 500 62,800
Zinc 446 56,017

Now if you want to figure a "tube" as you imply, you'd determine the
external volume and weight of the whole cylinder, then determine the
volume and weight of the internal cavity, then subtract.

So if the internal cavity is is one foot in radius its volume is
      pi * 1 * 1 * 10
 = pi * 10
   3.141 * 10
 = 31.41 cubic feet

Taking the steel weight above as a likely candidate for this, the
resulting tube would weigh:

  (125.6 cubic feet * 500 lbs/cu ft) - (31.41 cubic feet * 500 lbs/cu
ft)
 = 62800 - 15705
 = 47095 lbs

If the tube has "end pieces", these can be figured as short cylinders
and added to the total.

Enough math for today? ;-)
  
HTH

Stephen Posey
slposey@concentric.net

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