Volume of Solid of Revolution (About the line y = x)

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Discussion Overview

The discussion centers around calculating the volume of a solid of revolution formed by the area between the line y = x and the parabola y = x^2 when rotated about the axis y = x. The scope includes mathematical reasoning and exploration of different approaches to solving the problem.

Discussion Character

  • Exploratory
  • Mathematical reasoning
  • Debate/contested

Main Points Raised

  • One participant presents the problem as interesting and original, seeking to calculate the volume of the solid of revolution.
  • Another participant references an earlier thread on a similar problem, suggesting that it may not be entirely new.
  • Some participants express agreement on the value of the problem while acknowledging the existence of prior discussions.
  • There is a question raised about the complexity of the problem if an arbitrary direction is chosen for rotation.
  • One participant suggests that the only tricky part involves using arc length ds instead of dx for the volume element.
  • Another participant proposes that rotating the coordinates to standard form may simplify the problem significantly.

Areas of Agreement / Disagreement

Participants generally agree that the problem is worth discussing, but there are differing opinions on its complexity and the best approach to solving it. The discussion remains unresolved regarding the most effective method for calculating the volume.

Contextual Notes

Participants mention the need for careful consideration of the volume element and coordinate transformations, but specific assumptions or definitions are not fully explored.

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TL;DR
Volume of Solid of revolution about unusual axis
I found this problem, which I thought was interesting and somewhat original:

Calculate the volume of the solid of revolution of the area between the line ##y = x## and the parabola ##y = x^2## from ##x = 0## to ##x = 1## when rotated about the axis ##y = x##.
 
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I agree just wanted to be helpful here. When I first looked at it, I didn’t know how to tackle it until I saw the older post.

How intractable is it if an arbitrary direction is chosen?
 
jedishrfu said:
I agree just wanted to be helpful here. When I first looked at it, I didn’t know how to tackle it until I saw the older post.

How intractable is it if an arbitrary direction is chosen?
It's not particularly hard.
 
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I think the only tricky part is that the thickness of the typical volume element needs to be ds rather than dx; i.e., an increment of arc length along the parabola.
 
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Not even that, because the secret to any problem involving a rotated geometric figure is to rotate the co-ordinates ##\mathbf{x}' = \mathsf{R}\mathbf{x}## so that you have it in standard form.
 
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