- #1
kliker
- 104
- 0
I can't really understand something in spherical and cylinder coordinates
let me start with polar coordinates first
if we have for example x^2 + y^2 = 4 this is a circle with center (0,0) and radius 2
in polar coordinates x and y will be
x = rcosφ
y = rsinφ
0<=r<=2
0<=φ<=2π
here φ is from 0 to 2π but sometimes i see in problems they take φ to be from -π/2 to π/2
for example in a circle like this where you want to find the area
[PLAIN]http://img576.imageshack.us/img576/333/87706111.jpg
why we have to take here r from -π/2 to π/2? I mean, the definition says from 0 to 2π right?
this is my first question about polar coordinates
let's go to spherical
let's say we have this sphere x^2 + y^2 + z^2 = 1
x = rsinθcosφ
y = rsinθsinφ
z = rsinθ
0<=r<=1
now sometimes i see this kind of definition about θ and φ
-π/2<=θ<=π/2
0<=φ<=2π
or this
-π<=θ<=π
0<=φ<=π
how can i know which one to take in different kind of problems? also i can't understand the difference between the both, aren't they the same thing? and why don't we have θ in polar coordinates?
in cylinder we have the same definitions with polar coordinates except one thing, we have z too
i would appreciate any explanation provided, i can't find anything online, and our teacher didnt explain these stuff at all
thanks in advance
let me start with polar coordinates first
if we have for example x^2 + y^2 = 4 this is a circle with center (0,0) and radius 2
in polar coordinates x and y will be
x = rcosφ
y = rsinφ
0<=r<=2
0<=φ<=2π
here φ is from 0 to 2π but sometimes i see in problems they take φ to be from -π/2 to π/2
for example in a circle like this where you want to find the area
[PLAIN]http://img576.imageshack.us/img576/333/87706111.jpg
why we have to take here r from -π/2 to π/2? I mean, the definition says from 0 to 2π right?
this is my first question about polar coordinates
let's go to spherical
let's say we have this sphere x^2 + y^2 + z^2 = 1
x = rsinθcosφ
y = rsinθsinφ
z = rsinθ
0<=r<=1
now sometimes i see this kind of definition about θ and φ
-π/2<=θ<=π/2
0<=φ<=2π
or this
-π<=θ<=π
0<=φ<=π
how can i know which one to take in different kind of problems? also i can't understand the difference between the both, aren't they the same thing? and why don't we have θ in polar coordinates?
in cylinder we have the same definitions with polar coordinates except one thing, we have z too
i would appreciate any explanation provided, i can't find anything online, and our teacher didnt explain these stuff at all
thanks in advance
Last edited by a moderator: