Torus je obrtna ploha koja se dobija kada se rotira kružnica u trodimenzionom prostoru oko osekoplanarne sakružnicom , a koja ne dodiruje krug.
Torus Ako osa rotacije ne dodiruje kružnicu ploha ima oblik prstena i naziva se prstenasti torus ili samo torus. U slučaju da je osa rotacije tangenta kružnice dobijena ploha se naziva rog torus kada za osu rotacije uzmemo tetivu kružnice rezultujuća ploha je vretenasti torus. Kao takvaploha torus ima "rupu". Ako označimo sa c radijus od centra "rupe" do centra torusa, a sa a radijus torusa dolazimo do njegove parametarskejednačine :
{ x = ( c + a c o s v ) c o s u y = ( c + a c o s v ) s i n u z = a s i n v {\displaystyle {\begin{cases}x=(c+acosv)cosu\\y=(c+acosv)sinu\\z=asinv\end{cases}}} u , v ∈ [ 0 , 2 π ) {\displaystyle u,v\in [0,2\pi )} [ 1] gdje suu {\displaystyle u} v {\displaystyle v}
c {\displaystyle c} a {\displaystyle a} c {\displaystyle c} a {\displaystyle a}
Implicitna jednačina uKartezijevim koordinatama je
( c − x 2 + y 2 ) 2 + z 2 = a 2 , {\displaystyle \left(c-{\sqrt {x^{2}+y^{2}}}\right)^{2}+z^{2}=a^{2},}
Površina torusa je
P = ( 2 π r ) ( 2 π R ) = 4 π 2 c a {\displaystyle P=\left(2\pi r\right)\left(2\pi R\right)=4\pi ^{2}ca} [ 2] [ 3]
a zapremina
V = ( π a 2 ) ( 2 π c ) = 2 π 2 c a 2 {\displaystyle V=\left(\pi a^{2}\right)\left(2\pi c\right)=2\pi ^{2}ca^{2}}
V = 2 π 2 R r 2 , {\displaystyle \ V=2\pi ^{2}Rr^{2},}
Dokaz S = S 1 − S 2 , {\displaystyle \ S=S_{1}-S_{2},}
S 1 = π ( R + a ) 2 , {\displaystyle \ S_{1}=\pi (R+a)^{2},}
S 2 = π ( R − a ) 2 {\displaystyle \ S_{2}=\pi (R-a)^{2}}
PremaPitagorinoj teoremi imamo
a = r 2 − z 2 {\displaystyle \ a={\sqrt {r^{2}-z^{2}}}}
S 1 = π ( R + r 2 − z 2 ) 2 {\displaystyle \ S_{1}=\pi (R+{\sqrt {r^{2}-z^{2}}})^{2}} S 2 = π ( R − r 2 − z 2 ) 2 {\displaystyle \ S_{2}=\pi (R-{\sqrt {r^{2}-z^{2}}})^{2}}
S = π ( R + r 2 − z 2 ) 2 − π ( R − r 2 − z 2 ) 2 {\displaystyle \ S=\pi (R+{\sqrt {r^{2}-z^{2}}})^{2}-\pi (R-{\sqrt {r^{2}-z^{2}}})^{2}}
S = π [ ( R + r 2 − z 2 ) 2 − ( R − r 2 − z 2 ) 2 ] {\displaystyle \ S=\pi [(R+{\sqrt {r^{2}-z^{2}}})^{2}-(R-{\sqrt {r^{2}-z^{2}}})^{2}]}
S = π ( R 2 + 2 R r 2 − z 2 + r 2 − z 2 − R 2 + 2 R r 2 − z 2 − r 2 + z 2 ) {\displaystyle \ S=\pi (R^{2}+2R{\sqrt {r^{2}-z^{2}}}+r^{2}-z^{2}-R^{2}+2R{\sqrt {r^{2}-z^{2}}}-r^{2}+z^{2})}
S = π ( 2 R r 2 − z 2 + 2 R r 2 − z 2 ) {\displaystyle \ S=\pi (2R{\sqrt {r^{2}-z^{2}}}+2R{\sqrt {r^{2}-z^{2}}})}
S = 4 π R r 2 − z 2 {\displaystyle \ S=4\pi R{\sqrt {r^{2}-z^{2}}}}
V = ∫ − r r S ( z ) d z {\displaystyle \ V=\int \limits _{-r}^{r}S(z)\,dz}
V = ∫ − r r 4 π R r 2 − z 2 d z {\displaystyle \ V=\int \limits _{-r}^{r}4\pi R{\sqrt {r^{2}-z^{2}}}\,dz}
V = 4 π R ∫ − r r r 2 − z 2 d z {\displaystyle \ V=4\pi R\int \limits _{-r}^{r}{\sqrt {r^{2}-z^{2}}}\,dz}
∫ − r r r 2 − z 2 d z {\displaystyle \ \int \limits _{-r}^{r}{\sqrt {r^{2}-z^{2}}}\,dz}
d u d z = d r 2 − z 2 d z {\displaystyle \ {du \over dz}={d{\sqrt {r^{2}-z^{2}}} \over dz}}
d r 2 − z 2 d z d ( r 2 − z 2 ) d ( r 2 − z 2 ) {\displaystyle {d{\sqrt {r^{2}-z^{2}}} \over dz}{d(r^{2}-z^{2}) \over d(r^{2}-z^{2})}}
d r 2 − z 2 d ( r 2 − z 2 ) d ( r 2 − z 2 ) d z {\displaystyle {d{\sqrt {r^{2}-z^{2}}} \over d(r^{2}-z^{2})}{d(r^{2}-z^{2}) \over dz}}
d u d z = 1 2 ( r 2 − z 2 ) ( d r 2 d z 2 − d z 2 d z ) = 1 2 ( r 2 − z 2 ) ( 0 − 2 z ) = − 2 z 2 ( r 2 − z 2 ) = − z ( r 2 − z 2 ) {\displaystyle \ {du \over dz}={1 \over 2(r^{2}-z^{2})}({dr^{2} \over dz^{2}}-{dz^{2} \over dz})={1 \over 2(r^{2}-z^{2})}(0-2z)={-2z \over 2(r^{2}-z^{2})}=-{z \over (r^{2}-z^{2})}}
d u = − z r 2 − z 2 d z {\displaystyle \ du=-{z \over r^{2}-z^{2}}dz}
∫ − r r r 2 − z 2 d z = z r 2 − z 2 | − r r − ∫ − r r − z 2 r 2 − z 2 d z {\displaystyle \ \int \limits _{-r}^{r}{\sqrt {r^{2}-z^{2}}}\,dz=z{\sqrt {r^{2}-z^{2}}}{\bigg |}_{-r}^{r}-\int \limits _{-r}^{r}-{z^{2} \over {\sqrt {r^{2}-z^{2}}}}dz}
∫ − r r r 2 − z 2 d z = z r 2 − z 2 | − r r − ∫ − r r − z 2 − r 2 + r 2 r 2 − z 2 d z {\displaystyle \ \int \limits _{-r}^{r}{\sqrt {r^{2}-z^{2}}}\,dz=z{\sqrt {r^{2}-z^{2}}}{\bigg |}_{-r}^{r}-\int \limits _{-r}^{r}{-z^{2}-r^{2}+r^{2} \over {\sqrt {r^{2}-z^{2}}}}dz}
∫ − r r r 2 − z 2 d z = z r 2 − z 2 | − r r − ∫ − r r r 2 − z 2 r 2 − z 2 d z + ∫ − r r r 2 r 2 − z 2 d z {\displaystyle \ \int \limits _{-r}^{r}{\sqrt {r^{2}-z^{2}}}\,dz=z{\sqrt {r^{2}-z^{2}}}{\bigg |}_{-r}^{r}-\int \limits _{-r}^{r}{r^{2}-z^{2} \over {\sqrt {r^{2}-z^{2}}}}dz+\int \limits _{-r}^{r}{r^{2} \over {\sqrt {r^{2}-z^{2}}}}dz}
∫ − r r r 2 − z 2 d z = z r 2 − z 2 | − r r − ∫ − r r r 2 − z 2 d z + r 2 ∫ − r r 1 r 2 − z 2 d z {\displaystyle \ \int \limits _{-r}^{r}{\sqrt {r^{2}-z^{2}}}\,dz=z{\sqrt {r^{2}-z^{2}}}{\bigg |}_{-r}^{r}-\int \limits _{-r}^{r}{\sqrt {r^{2}-z^{2}}}dz+r^{2}\int \limits _{-r}^{r}{1 \over {\sqrt {r^{2}-z^{2}}}}dz}
∫ − r r r 2 − z 2 d z + ∫ − r r r 2 − z 2 d z = z r 2 − z 2 | − r r + r 2 ∫ − r r 1 r 2 ( 1 − z 2 r 2 ) d z {\displaystyle \ \int \limits _{-r}^{r}{\sqrt {r^{2}-z^{2}}}\,dz+\int \limits _{-r}^{r}{\sqrt {r^{2}-z^{2}}}\,dz=z{\sqrt {r^{2}-z^{2}}}{\bigg |}_{-r}^{r}+r^{2}\int \limits _{-r}^{r}{1 \over {\sqrt {r^{2}(1-{z^{2} \over r^{2}})}}}dz}
2 ∫ − r r r 2 − z 2 d z = z r 2 − z 2 | − r r + r 2 ∫ − r r 1 ( 1 − ( z r ) 2 ) d ( z r ) {\displaystyle \ 2\int \limits _{-r}^{r}{\sqrt {r^{2}-z^{2}}}\,dz=z{\sqrt {r^{2}-z^{2}}}{\bigg |}_{-r}^{r}+r^{2}\int \limits _{-r}^{r}{1 \over {\sqrt {(1-({z \over r})^{2})}}}d({z \over r})}
∫ − r r r 2 − z 2 d z = z r 2 − z 2 + r 2 arcsin ( z r ) 2 | − r r {\displaystyle \ \int \limits _{-r}^{r}{\sqrt {r^{2}-z^{2}}}\,dz={z{\sqrt {r^{2}-z^{2}}}+r^{2}\arcsin({z \over r}) \over 2}{\bigg |}_{-r}^{r}}
∫ − r r r 2 − z 2 d z = r r 2 − r 2 + r 2 arcsin ( r r ) 2 − − r r 2 − ( − r ) 2 + r 2 arcsin ( ( − r ) r ) 2 {\displaystyle \ \int \limits _{-r}^{r}{\sqrt {r^{2}-z^{2}}}\,dz={r{\sqrt {r^{2}-r^{2}}}+r^{2}\arcsin({r \over r}) \over 2}-{-r{\sqrt {r^{2}-(-r)^{2}}}+r^{2}\arcsin({(-r) \over r}) \over 2}}
∫ − r r r 2 − z 2 d z = r 2 arcsin ( 1 ) − r 2 arcsin ( − 1 ) 2 {\displaystyle \ \int \limits _{-r}^{r}{\sqrt {r^{2}-z^{2}}}\,dz={r^{2}\arcsin({1})-r^{2}\arcsin({-1}) \over 2}}
∫ − r r r 2 − z 2 d z = r 2 2 ( π 2 − ( − π 2 ) ) {\displaystyle \ \int \limits _{-r}^{r}{\sqrt {r^{2}-z^{2}}}\,dz={r^{2} \over 2}({\pi \over 2}-(-{\pi \over 2}))}
∫ − r r r 2 − z 2 d z = r 2 π 2 {\displaystyle \ \int \limits _{-r}^{r}{\sqrt {r^{2}-z^{2}}}\,dz={r^{2}\pi \over 2}}
V = 4 π R ∫ − r r r 2 − z 2 d z → V = 4 π R r 2 π 2 {\displaystyle \ V=4\pi R\int \limits _{-r}^{r}{\sqrt {r^{2}-z^{2}}}\,dz\to V=4\pi R{r^{2}\pi \over 2}}
V = 2 π 2 R r 2 , {\displaystyle \ V=2\pi ^{2}Rr^{2},}
Parametarska jednačina prstenastog torusa je
{ x = ( c + a c o s v ) c o s u y = ( c + a c o s v ) s i n u z = a s i n v {\displaystyle {\begin{cases}x=(c+acosv)cosu\\y=(c+acosv)sinu\\z=asinv\end{cases}}}
zau , v ∈ [ 0 , 2 π ) {\displaystyle u,v\in [0,2\pi )} i a > c {\displaystyle ia>c}
Koficienti prve kvadratne forme su
E = ( c + a c o s v ) 2 {\displaystyle E=(c+acosv)^{2}} F = 0 {\displaystyle F=0} G = a 2 {\displaystyle G=a^{2}} dok za koeficiente druge kvadratne forme dobijamo
L = − ( c + a c o s v ) c o s v {\displaystyle L=-(c+acosv)cosv} M = 0 {\displaystyle M=0} N = − a {\displaystyle N=-a} Gausova i srednja kriva su date sa:
K G = c o s v a ( c + a c o s v ) {\displaystyle K_{G}={\frac {cosv}{a(c+acosv)}}}
K S = − c + 2 a c o s v 2 a ( c + a c o s v ) {\displaystyle K_{S}={\frac {-c+2acosv}{2a(c+acosv)}}}
Uzimajući u jednačini
{ x = ( c + a c o s v ) c o s u y = ( c + a c o s v ) s i n u z = a s i n v {\displaystyle {\begin{cases}x=(c+acosv)cosu\\y=(c+acosv)sinu\\z=asinv\end{cases}}}
da jec = a {\displaystyle c=a} [ 4]
{ x = a ( 1 + c o s v ) c o s u y = a ( 1 + c o s v ) s i n u z = a s i n v {\displaystyle {\begin{cases}x=a(1+cosv)cosu\\y=a(1+cosv)sinu\\z=asinv\end{cases}}}
Za koeficiente prve kvadratne forme dobijamo:
E = 4 a 2 c o s 4 ( 1 2 v ) {\displaystyle E=4a^{2}cos^{4}({\frac {1}{2}}v)} F = 0 {\displaystyle F=0} G = a 2 {\displaystyle G=a^{2}} dok su koeficienti druge kvadratne forme rog torusa:
L = − 2 a c o s 2 ( 1 2 ) c o s v {\displaystyle L=-2acos^{2}({\frac {1}{2}})cosv} M = 0 {\displaystyle M=0} N = − a {\displaystyle N=-a} Kod vretenastog torusa parametarska jednačina, formule za koeficiente prve i druge kvadratne forme i formule za izračunavanje srednje i Gausove krive su iste kao i kod prstenastog torusa, uz uslovc < a {\displaystyle c<a}
Rotacione površi i njihova vizuelizacija u programskom paketu Mathematica Niš, novembar 2013. [mrtav link
↑ „parametarska jednačina 06. juli 1995” . Arhivirano izoriginala na datum 2019-05-20. Pristupljeno 2016-05-01 . ↑ ring torus ↑ površina torusa ↑ Horn torus Niš novembar 2013 [mrtav link 
