 Sphere Volume. - Printable Version +- HP Forums (https://www.hpmuseum.org/forum) +-- Forum: Not HP Calculators (/forum-7.html) +--- 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! 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