Going from Spherical coordinates to Cartesian

In summary, the conversation discusses converting a point from spherical coordinates to Cartesian coordinates. The attempt at a solution is provided, but it is mentioned that there may be a difference in conventions for the meaning of the angles in spherical coordinates, depending on whether it is a mathematics or engineering class. The final answer is given as (-4.24264068712, -4.24264068712, 3.67381906147E-16).
  • #1
the7joker7
113
0

Homework Statement



Convert the point `(rho,theta,phi) = (6, (5pi)/4, pi/2)` to Cartesian coordinates. Give answers as positive values, either as expressions, or decimals to one decimal place.

The Attempt at a Solution



{x}=r*sintheta*cosphi
{y}=r*sintheta*sinphi
{z}=r*costheta

So

x = 6*sin(5pi/4)*cos(pi/2)
y = 6*sin(5pi/4)*sin(pi/2)
z = 6*cos(5pi/4)

x = 0
y = -4.242640687 (+2pi)
z = -4.242640687 (+2pi)

What did I do wrong?
 
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  • #2
Don't know. It looks reasonable so far. But you should be warned that mathematicians and physicists use different convention for the meaning of the angles in spherical coordinates. Are you sure you got the coordinate change from the same source as the problem? But I'm not sure what the (+2pi) is supposed to mean.
 
  • #3
Because my answer is negative, don't I add 2pi to get the correct positive answer, as is the law of angles in this format?

FTR, here's the right answer.

`[(-4.24264068712,-4.24264068712,3.67381906147E-16)]`
 
  • #4
the7joker7 said:
Because my answer is negative, don't I add 2pi to get the correct positive answer, as is the law of angles in this format?

FTR, here's the right answer.

`[(-4.24264068712,-4.24264068712,3.67381906147E-16)]`

Your answer is {x,y,z}. Those aren't angles. You can't add anything to them. Where did you get that 'answer'? I'm guessing because of the E-16 from some kind a 'calculator device'. Are you sure that is using the same conventions as the problem source?
 
  • #5
Yeah, it's an online homework system. WAMAP.
 
  • #6
Oh, great. I don't know what WAMAP means either. But from the -4.24264068712 and E-16 which should in any reasonable universe be written as '0', you weren't completely off.
 
  • #7
Is this an engineering class or a mathematics class?

The reason I ask is that engineers swap "[itex]\theta[/itex]" and "[itex]\phi[/itex]" from what mathematicians use. Is [itex]\phi[/itex] the "co-latitude" and [itex]\theta[/itex] the "longitude" or vice-versa?
 

1. What are spherical coordinates?

Spherical coordinates are a three-dimensional coordinate system that is commonly used in mathematics and physics to describe the position of a point in space. They consist of a radial distance from the origin, an angle measured from the positive z-axis, and an angle measured from the positive x-axis.

2. How do you convert from spherical coordinates to Cartesian coordinates?

To convert from spherical coordinates to Cartesian coordinates, you can use the following equations:
x = r sinθ cosφ
y = r sinθ sinφ
z = r cosθ
where r is the radial distance, θ is the angle measured from the positive z-axis, and φ is the angle measured from the positive x-axis.

3. What is the benefit of using spherical coordinates?

Spherical coordinates have several benefits, including simplifying calculations for objects with spherical symmetry and making it easier to describe the position of an object in space relative to a fixed point. They are also commonly used in fields such as astronomy and physics.

4. Can you convert from Cartesian coordinates to spherical coordinates?

Yes, you can convert from Cartesian coordinates to spherical coordinates using the following equations:
r = √(x² + y² + z²)
θ = tan⁻¹(y/x)
φ = cos⁻¹(z/√(x² + y² + z²))
where x, y, and z are the coordinates in the Cartesian system.

5. Are spherical coordinates used in real-world applications?

Yes, spherical coordinates are used in various real-world applications, such as navigation systems, satellite tracking, and geographic information systems. They are also commonly used in physics and engineering to describe the position of objects in space or to solve problems involving spherical symmetry.

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