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Posted by Bobk207 on November 11, 2006, 4:01 pm
Mark wrote:
> > For all you engineers/techs out there..... I want to mold a couple of
> > concrete or quikrete balls about the size of a 8" or 10" cannon ball
> > depending on the finished weight.
> Well, let's see (fires up Excel...)
> The formula for the volume of a sphere is 4/3 pi * (radius)^3.
> That's about 268 cubic inches for the 8" sphere, and 524 cubic
> inches for the 10" sphere.
> I have seen weights for conrete listed from 2000lbs per cy
> to 4000lbs per cy. I think 2000 is too low; the local
> ready-mix plant claims 3000.
> Assuming that concrete has a nominal weight of 3000 lbs per
> cubic yard, your 8" and 10" cannonballs would weigh about
> 17 lbs and 34 lbs respectively.
> At 4000, your cannonballs would weigh 23 lbs and 45 lbs
> respectively.
> -Mark
I would agree with the 23 & 45 lb answers ........but your other
numbers seem a little low for normal weight concrete
"normal" weight concrete is about 140 to 150 pounds per ft^3 (3800 to
4000 lbs per cy)
Your local mix plant claims 3000 lbs per cy? That's down in the range
of lightweight concretes. Maybe they were talking about compressive
strengths
Are you sure you're not quoting compressive strengths (2000 to 4000
PSI) & the numbers just turn out close to density as well? The number
I always use for weight calcs is 150 (lbs/ft^3), that might be a touch
high but it's very close.
In any case the concrete balls will be ~23 & ~45 lbs
to determine weights of other sized balls
as Mark calc'd the volume
4/3 pi * radius ^3. (in^3) * 150 (lbs/ft^3) / 1728 (in^3/ft^3)
units cancel & you're left with lbs
be careful, don't blow yourself up
cheers
Bob
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> concrete or quikrete balls about the size of a 8" or 10" cannon ball
> depending on the finished weight. If I can get a concrete conversion
> weight formula that would be super too.....
> Also, is there any relatively cheap molding material that could be used
> that would HEAVIER?
> -Thanks for any help!
>