Volume between sphere and outside cylinder.

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SUMMARY

The discussion focuses on calculating the volume bounded by the sphere defined by the equation x² + y² + z² = 4 and the exterior of the cylinder described by x² + y² = 2x. Participants suggest using cylindrical coordinates for integration, specifically the limits ∫(θ=0,2π)dθ∫(r=1,2)dr∫(z=0,sqrt(4-r²)). They emphasize the importance of accurately determining the limits for z, r, and θ, particularly where the sphere intersects the cylinder. The final volume removed by the cylinder is approximately 9.644, leaving a volume of 23.85 in the sphere.

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  • Cylindrical coordinates and their application in volume integration
  • Understanding of the equations of spheres and cylinders
  • Knowledge of integration techniques in multiple dimensions
  • Familiarity with Cartesian and polar coordinate transformations
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  • #31
In cylindrical, you have z, r, theta. What will be your integration order?
As a check on the answer, numerically I get about 9.66 for the volume removed by the cylinder, leaving 23.85 in the sphere. Sound right? Still working on the analytic result using Cartesian.
 
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  • #32
haruspex said:
In cylindrical, you have z, r, theta. What will be your integration order?
As a check on the answer, numerically I get about 9.66 for the volume removed by the cylinder, leaving 23.85 in the sphere. Sound right? Still working on the analytic result using Cartesian.

I get 9.644049708034451 for the volume removed. So that sounds about right. I integrated dz first, dr second and dtheta third. peripatein had the right general idea in the first post, except that the r factor in the measure was left out, the z limits are wrong, the r limits are wrong and the theta limits are also wrong. It just needs to be fixed. But seriously, if you are still working on the result in Cartesian, I'd give it up unless it's become an obsession. It's HARD to do that way. It's not THAT much of a challenge in cylindrical.
 
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  • #33
Dick said:
I get 9.644049708034451 for the volume removed. So that sounds about right. I integrated dz first, dr second and dtheta third. peripatein had the right general idea in the first post, except that the r factor in the measure was left out, the z limits are wrong, the r limits are wrong and the theta limits are also wrong. It just needs to be fixed. But seriously, if you are still working on the result in Cartesian, I'd give it up unless it's become an obsession. It's HARD to do that way. It's not THAT much of a challenge in cylindrical.
I came to the same conclusion :biggrin:. In the end, I did it with a single integration. In the z plane, the area to be removed is the intersection of two circles. That turns into the sum of two sectors minus the sum of two triangles, so I could write those straight down. Final result is the removal of 16π/3-64/9, leaving 16π/3+64/9. Neatest way to express it is that it leaves 16/9 in the hemisphere it lies in.
 

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