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+--- Forum: Not quite HP Calculators - but related (/forum-8.html)
+--- Thread: Sphere Volume. (/thread-5964.html)
Sphere Volume. - ggauny@live.fr - 03-31-2016 11:29 AM
Hi,
All of us know that Sphere Volume is calculate like this :
4/3(PI*R^3)
A short cut from Bill Kolb is : "240 'D-R' R^3 *",
But NASA (on his siteweb) say (PI*D^3)/6.
It is more easy and less steps, even I dont' see how go from first formulae to
NASA one ?
RE: Sphere Volume. - PANAMATIK - 03-31-2016 11:56 AM
(03-31-2016 11:29 AM)ggauny@live.fr Wrote: Hi,
All of us know that Sphere Volume is calculate like this :
4/3(PI*R^3)
A short cut from Bill Kolb is : "240 'D-R' R^3 *",
But NASA (on his siteweb) say (PI*D^3)/6.
It is more easy and less steps, even I dont' see how go from first formulae to
NASA one ?
PI * R * R * R * 8/6 =
PI * 2R * 2R * 2R * 1/6
Bernhard
RE: Sphere Volume. - jebem - 03-31-2016 11:58 AM
Hi, Gérard,
Well, I forgot almost mt math after so much brain damage caused by good life and drinks... .)
Let me try:
V = 4/3 * PI * R^3
Also, we know that D = 2 * R; then R = D/2
If we replace R for D/2 in the initial equation, we get:
V = 4/3 * PI * (D/2)^3
which can also be written as:
V = 4/3 * PI * D^3 / 2^3
Or:
V = 4/3 * PI * D^3 / 8
Or:
V = 4/(3 * 8) * PI * D^3
Or:
V = 4/24 * PI * D^3
Or:
V = 1/6 * PI * D^3
Or:
V = (PI * D^3)/6
RE: Sphere Volume. - Dieter - 03-31-2016 12:46 PM
(03-31-2016 11:29 AM)ggauny@live.fr Wrote: 4/3(PI*R^3)
(...)
But NASA (on his siteweb) say (PI*D^3)/6.
It is more easy and less steps, even I dont' see how go from first formulae to
NASA one ?
Take the first formula and replace R with D/2.
What do you get?
Dieter
RE: Sphere Volume. - ggauny@live.fr - 03-31-2016 02:23 PM
Of course I have see the answers, but me I find :
4/3(Pi*(D/2)^3)
8/6(3*Pi*(D/6)^3)
and if I divise all by 6 I obtain :
8(3*Pi*D^3)
so it is 24*Pi*D^3 and it is false !
desolation !
RE: Sphere Volume. - TASP - 03-31-2016 03:32 PM
when's the last time anyone had to fill a sphere with beer ??
(just askin',
)
RE: Sphere Volume. - ggauny@live.fr - 03-31-2016 04:17 PM
Of course I prefer drink the beer, it is less complicated then do theses calculs !
LOL.
RE: Sphere Volume. - jebem - 03-31-2016 04:34 PM
(03-31-2016 03:32 PM)TASP Wrote: when's the last time anyone had to fill a sphere with beer ??
(just askin',
You have just brought a lot of past memories to my mind, from my good old times spent in Ghent (Belgium) studying computer technologies and of course, drinking the famous Kwak beer.
Not a complete sphere, but still it was great fun drinking it!
![[Image: Kwak.jpg]](https://upload.wikimedia.org/wikipedia/commons/4/4e/Kwak.jpg)
RE: Sphere Volume. - TASP - 03-31-2016 05:21 PM
The sphere thing is interesting from a computational standpoint, but I'm damned if I can think of a practical application. We've ruled out beer, what else is there ??
RE: Sphere Volume. - ggauny@live.fr - 03-31-2016 06:55 PM
Yes, if we are not careful all the beer on the face, same with glass like a boot of cow-boy !
RE: Sphere Volume. - Dieter - 03-31-2016 07:20 PM
(03-31-2016 02:23 PM)ggauny@live.fr Wrote: Of course I have see the answers, but me I find :
4/3(Pi*(D/2)^3)
8/6(3*Pi*(D/6)^3)
and if I divise all by 6 I obtain :
8(3*Pi*D^3)
so it is 24*Pi*D^3 and it is false !
You obviously forgot some basic math rules.
First of all, forget the brackets (except around d/2). All values are faktors, so there is no need to set brackets.
Then, (a/b)^n = a^n / b^n.
So...
4/3 * pi * (d/2)^3
= 4/3 * pi * d^3 / 2^3
= 4/3 * pi * d^3 / 8
= 4/3/8 * pi * d^3
= 4/24 * pi * d^3
= pi * d^3 / 6
Dieter