SOLIDS OF REVOLUTION SOLVER
Disk, Washer & Cylindrical Shell Methods
Calculus & 3D Integration
3D Solid Volume Analysis
Recommended Method
Disk / Washer
Calculated Volume ($V$)
20.1062
Exact Volume Multiplier ($\pi$-notation)
6.4000 π
Step-by-Step Integral Derivation
Volume of Solids of Revolution: Disk, Washer & Cylindrical Shell Methods
Calculating the volume of a solid of revolution involves rotating a two-dimensional region bounded by functions around a specified line (the axis of revolution) in three-dimensional space. Selecting between the Disk, Washer, and Cylindrical Shell methods depends on the axis orientation and the variable of integration.
1. Summary of Rotational Methods
| Method | Axis of Revolution | Slice Geometry | Integral Formula |
|---|---|---|---|
| Disk Method | Parallel to slice axis ($y = c$) | Solid circular cross-section | $$V = \pi \int_{a}^{b} [R(x)]^2 \, dx$$ |
| Washer Method | Parallel to slice axis ($y = c$) | Circular cross-section with hole | $$V = \pi \int_{a}^{b} \left( [R(x)]^2 - [r(x)]^2 \right) \, dx$$ |
| Cylindrical Shell Method | Perpendicular to slice axis ($x = c$) | Thin concentric cylindrical shell | $$V = 2\pi \int_{a}^{b} r(x) h(x) \, dx$$ |
2. Choosing Between Washer and Shell Methods
- Washer Method (dx): Best when rotating around horizontal lines ($y = c$) and function curves are naturally given as $y = f(x)$. Slices are perpendicular to the axis of rotation.
- Cylindrical Shell Method (dx): Ideal when rotating around vertical lines ($x = c$) without needing to invert $y = f(x)$ into $x = f^{-1}(y)$. Slices are parallel to the axis of rotation.
Frequently Asked Questions
What happens when the axis of rotation is shifted?
When rotating around $y = c$ or $x = c$ instead of the coordinate axes ($y = 0$ or $x = 0$), adjust the radius expressions accordingly: $R(x) = |f(x) - c|$ or $r(x) = |x - c|$.
Can a volume generated by revolution be negative?
No. Absolute values or squared radius terms ensure $R(x) \ge r(x) \ge 0$, rendering volume results non-negative.
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