Cone Frustum Lateral Area⚠ unverified
Geometry / Solid · Lateral area of a conical frustum
Parameters
| Input | Symbol | Unit | Default | Description |
|---|---|---|---|---|
| r1 | R | m | 3 | Larger radius |
| r2 | r | m | 2 | Smaller radius |
| l | l | m | 5 | Slant height |
| Output | Symbol | Unit | Description |
|---|---|---|---|
| A | A | m^2 | Lateral area |
The science & history
Understanding the Parameters
- R (m) — Larger radius.
- r (m) — Smaller radius.
- l (m) — Slant height.
- Output A (m^2) — Lateral area.
How to Calculate
- Enter Larger radius as
r1(default 3 m). Use the unit menu when you need a different unit. - Enter Smaller radius as
r2(default 2 m). Use the unit menu when you need a different unit. - Enter Slant height as
l(default 5 m). Use the unit menu when you need a different unit. - Click Calculate. The card evaluates $A = \pi(R+r)l$ and shows the result in the declared output unit; Result in (when present) converts that number.
The Science: A Rigorous Derivation (Approaching a Proof)
Solid Euclidean geometry extends the plane metric to $\mathbb{R}^3$. Volume is the unique translation-invariant measure assigning $1$ to the unit cube; Cavalieri's principle (if two solids have equal cross-sectional area at every height, they have equal volume) gives the pyramid and cone factor $\tfrac13$ from the prism. Surface area is the $2$-dimensional Hausdorff measure of the boundary. A sphere is the unique surface of constant curvature; its volume and area are the classical isoperimetric extrema.
Dimensional check. The declared output unit is m^2; ToolBox evaluates the
formula in SI (radians internally for every trigonometric call) and python-calc converts to
the unit on the card.
History and Development
- Euclid, Elements Books XI–XIII. Parallelepipeds, pyramids, and the five regular solids.
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Archimedes, On the Sphere and Cylinder. $V = \tfrac43\pi r^3$ and $A = 4\pi r^2$, of which he was so proud that a sphere-in-cylinder was placed on his tomb. He also treated spheroids, conoids, and the frustum.
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Eudoxus / method of exhaustion. The $\tfrac13$ pyramid factor predates Euclid; Archimedes makes the limiting argument rigorous.
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Kepler, Cavalieri, 17th century. Infinitesimal arguments that become calculus; the ellipsoid $V = \tfrac43\pi abc$ is the affine image of a sphere (linear maps scale volume by $\det$).
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Modern vector calculus. Divergence theorem: the volume formulae are $\tfrac13\int\mathbf{r}\cdot d\mathbf{S}$ over the boundary.
Related Concepts: Cube Volume, Box Volume, Prism Volume, Pyramid Volume, Cone Volume, Cylinder Volume, Sphere Volume, Hemisphere Volume