Calculating Volume with Integration: 4/3(pi)r^3

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    Integration Volume
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Discussion Overview

The discussion revolves around the calculation of the volume of a sphere using integration techniques. Participants explore different methods, interpretations, and formulas related to the volume and surface area of geometric shapes, particularly focusing on the expression 4/3(pi)r^3.

Discussion Character

  • Exploratory
  • Technical explanation
  • Conceptual clarification
  • Debate/contested
  • Mathematical reasoning

Main Points Raised

  • One participant notes that integrating 2(pi)r yields (pi)r^2, and further integration leads to 1/3(pi)r^3, questioning how to arrive at 4/3(pi)r^3.
  • Another suggests differentiating the volume expression to find a suitable interpretation of the result.
  • A participant argues that disks are not the infinitesimal shells that contribute to the volume of a solid sphere.
  • There is a proposal to use half of the area formula and the disk method for rotation to potentially derive 4/3(pi)r^3, although the participant expresses uncertainty due to being busy.
  • One participant mentions a different technique involving adding up the shells of surface area of a sphere.
  • Another expresses confusion about using the surface area formula for a sphere and contemplates integrating from 0 to r, while also questioning the significance of 1/3(pi)r^3 and whether it relates to the volume of a cylinder.
  • A later reply points out that the surface area of a sphere is 4(pi)r^2.

Areas of Agreement / Disagreement

Participants do not reach a consensus on the methods for calculating the volume of a sphere, and multiple competing views remain regarding the appropriate techniques and interpretations.

Contextual Notes

Some participants express uncertainty about the formulas and methods discussed, and there are unresolved questions about the relationships between the volume of different geometric shapes.

Silverious
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If I intergrate 2(pi)r I get (pi)r^2

If I integrate that I get 1/3 (pi)r^3, which is close to the volume of a sphere. But where do I get a 4/3(pi)r^3 ?
 
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Differentiate the volume expression, and find a suitable interpretation of the result.
 
Last edited:
beacause disks are not the infinitesimal shells that add up to a solid sphere
 
Would it work if I used half of the area forumula, and used the disk method to rotate it about an axis? Should that give me 4/3(pi)r^3?

I would find out for myself but I'm a little busy.

Thanks for the replies.
 
that's a different technique: add up the shells of surface area of a sphere
 
OKay I'm starting to understand.

So I use the surface area formula(for a sphere). Integrate from 0 to r? :rolleyes:

Edit: Oh my god. I feel so stupid...

You see, I didn't know the formula for the surface area of a sphere. ...

Oh well. Anyways, uum. So then, what is 1/3(pi)r^3? Without looking it up, making a wild guess...is it the volume of a cylinder?

Edit2: I really need to stop thinking... I have no clue what I'm talking about. So is 1/3(pi)r^3 just nonsense?

Edit3: Interesting that a cone's volume is 1/3(pi)r^2 h. Good I have much time to think about it.
 
Last edited:
the surface area of a sphere is 4(pi)r^2
 

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