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| The '''surface area''' of a solid object is the total area of the object's faces and curved surfaces. The mathematical definition of surface area in the presence of curved surfaces is considerably more involved than the definition of [[arc length]] of one-dimensional curves, or of the surface area for [[polyhedra]] (i.e., objects with flat polygonal [[Face (geometry)|faces]]), for which the surface area is the sum of the areas of its faces. Smooth surfaces, such as a [[sphere]], are assigned surface area using their representation as [[parametric surface]]s. This definition of surface area is based on methods of [[infinitesimal]] [[calculus]] and involves [[partial derivative]]s and [[double integration]].
| | == アウト彼女、 == |
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| A general definition of surface area was sought by [[Henri Lebesgue]] and [[Hermann Minkowski]] at the turn of the twentieth century. Their work led to the development of [[geometric measure theory]], which studies various notions of surface area for irregular objects of any dimension. An important example is the [[Minkowski content]] of a surface.
| | 真顔で。<br><br>は劉ユーミンもつれたくない [http://www.dmwai.com/webalizer/kate-spade-5.html ケイトスペード バッグ アウトレット] 'この哀れな人生、お金が。ていない、それを忘れて忘れて」。<br><br>'私はちょうど転送されていませんでした。'古い魏誠実な本格的 [http://www.dmwai.com/webalizer/kate-spade-13.html ケイトスペード バッグ ショルダー]。<br>「ターン？ '<br>劉ユーミン怒っアップ [http://www.dmwai.com/webalizer/kate-spade-13.html ケイトスペード 人気バッグ]。<br><br>'私は'誰が戻って劉ユーミンを流れる電流のように聞こえること、墜落し、彼は突然地面に凍結した。<br><br>「詐欺」劉ユーミンは即座に反応する [http://www.dmwai.com/webalizer/kate-spade-8.html マザーズバッグ ケイトスペード]。<br>アウト彼女、<br>後半、銃声とは異なり、完全に完全に完全に [http://www.dmwai.com/webalizer/kate-spade-6.html ケイトスペード マザーズバッグ]......でも、無限の武器でQiqiの梁、空へ6穏やかなホワイトカラーの服モーメントリフトの後に遮断土が、それはより強力な銃ですすべてのファンを持つ、劉ユーミンモーメント鼻づまりの口の目ランツィ咳を埋め、白で囲まれて充填した。<br>粉末銃、火、ピンクのシェルカバレッジ内の1つの4平方メートル、即座にギャングの戦いを一掃するために十数ヘアスプレー、1咳絞り出し中<br>、ちょうどタンク小麦粉から登るように少数のマウスの、劉ユーミンは遠くから最近、2つのラウンド |
| | | 相关的主题文章： |
| ==
| | <ul> |
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| While the areas of many simple surfaces have been known since antiquity, a rigorous mathematical ''definition'' of area requires a great deal of care.
| | <li>[http://www.collinsmuseum.com/cgi-bin/ibook/ibook.cgi http://www.collinsmuseum.com/cgi-bin/ibook/ibook.cgi]</li> |
| This should provide a function
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| | | <li>[http://www.bjhforum.co.uk/woolly/guestbook.cgi http://www.bjhforum.co.uk/woolly/guestbook.cgi]</li> |
| : <math> S \mapsto A(S) </math>
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| | | <li>[http://ftkx17.com/plus/feedback.php?aid=327 http://ftkx17.com/plus/feedback.php?aid=327]</li> |
| which assigns a positive [[real number]] to a certain class of [[surface]]s that satisfies several natural requirements. The most fundamental property of the surface area is its '''additivity''': ''the area of the whole is the sum of the areas of the parts''. More rigorously, if a surface ''S'' is a union of finitely many pieces ''S''<sub>1</sub>, …, ''S''<sub>''r''</sub> which do not overlap except at their boundaries, then
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| : <math> A(S) = A(S_1) + \cdots + A(S_r). </math>
| | </ul> |
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| Surface areas of flat polygonal shapes must agree with their geometrically defined [[area]]. Since surface area is a geometric notion, areas of [[congruence (geometry)|congruent]] surfaces must be the same and the area must depend only on the shape of the surface, but not on its position and orientation in space. This means that surface area is invariant under the [[Euclidean group|group of Euclidean motions]]. These properties uniquely characterize surface area for a wide class of geometric surfaces called ''piecewise smooth''. Such surfaces consist of finitely many pieces that can be represented in the [[parametric surface|parametric form]]
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| : <math> S_D: \vec{r}=\vec{r}(u,v), \quad (u,v)\in D </math>
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| with a [[continuously differentiable]] function <math>\vec{r}.</math> The area of an individual piece is defined by the formula
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| : <math> A(S_D) = \iint_D\left |\vec{r}_u\times\vec{r}_v\right | \, du \, dv. </math>
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| Thus the area of ''S''<sub>''D''</sub> is obtained by integrating the length of the normal vector <math>\vec{r}_u\times\vec{r}_v</math> to the surface over the appropriate region ''D'' in the parametric ''uv'' plane. The area of the whole surface is then obtained by adding together the areas of the pieces, using additivity of surface area. The main formula can be specialized to different classes of surfaces, giving, in particular, formulas for areas of graphs ''z'' = ''f''(''x'',''y'') and [[surface of revolution|surfaces of revolution]].
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| One of the subtleties of surface area, as compared to [[arc length]] of curves, is that surface area cannot be defined simply as the limit of areas of polyhedral shapes approximating a given smooth surface. It was demonstrated by [[Hermann Schwarz]] that already for the cylinder, different choices of approximating flat surfaces can lead to different limiting values of the area (Known as [[Schwarz's paradox]].)
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| <ref name=sch1>http://www.math.usma.edu/people/Rickey/hm/CalcNotes/schwarz-paradox.pdf</ref>
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| .<ref name=sch2>http://mathdl.maa.org/images/upload_library/22/Polya/00494925.di020678.02p0385w.pdf</ref>
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| Various approaches to a general definition of surface area were developed in the late nineteenth and the early twentieth century by [[Henri Lebesgue]] and [[Hermann Minkowski]]. While for piecewise smooth surfaces there is a unique natural notion of surface area, if a surface is very irregular, or rough, then it may not be possible to assign an area to it at all. A typical example is given by a surface with spikes spread throughout in a dense fashion. Many surfaces of this type occur in the study of [[fractal]]s. Extensions of the notion of area which partially fulfill its function and may be defined even for very badly irregular surfaces are studied in [[geometric measure theory]]. A specific example of such an extension is the [[Minkowski content]] of the surface.
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| == Common formulas ==
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| {| class="wikitable"
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| |+ Surface areas of common solids
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| |-
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| !Shape
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| !Equation
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| !Variables
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| |-
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| |[[Cube]]
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| |<math> 6s^2 \, </math>
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| |''s'' = side length
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| |-
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| |[[Rectangular prism]]
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| |<math> 2(\ell w + \ell h + wh) \, </math>
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| |''ℓ'' = length, ''w'' = width, ''h'' = height
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| |-
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| |[[Triangular prism]]
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| |<math> bh + l(a + b + c) </math>
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| |''b'' = base length of triangle, ''h'' = height of triangle, ''l'' = distance between triangles, ''a'', ''b'', ''c'' = sides of triangle
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| |-
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| |All [[Prism (geometry)|Prisms]]
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| |<math> 2B + Ph \, </math>
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| |''B'' = the area of one base, ''P'' = the perimeter of one base, ''h'' = height
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| |-
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| |[[Sphere]]
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| |<math> 4\pi r^2 = \pi d^2\, </math>
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| |''r'' = radius of sphere, ''d'' = diameter
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| |-
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| |[[Spherical lune]]
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| |<math> 2r^2\theta \, </math>
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| |''r'' = radius of sphere, ''θ'' = [[dihedral angle]]
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| |-
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| |[[Torus]]
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| |<math> (2\pi r)(2\pi R) = 4\pi^2 Rr</math>
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| |''r'' = minor radius, ''R'' = major radius
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| |-
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| |Closed [[Cylinder (geometry)|cylinder]]
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| |<math> 2\pi r^2 + 2\pi rh = 2\pi r(r+h) \, </math>
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| |''r'' = radius of the circular base, ''h'' = height of the cylinder
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| |-
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| |Lateral surface area of a [[cone (geometry)|cone]]
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| |<math> \pi r \left(\sqrt{r^2+h^2}\right) = \pi rs \, </math>
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| |<math> s = \sqrt{r^2+h^2} </math><br>
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| ''s'' = slant height of the cone,<br>
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| ''r'' = radius of the circular base,<br>
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| ''h'' = height of the cone
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| |-
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| |Full surface area of a cone
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| |<math> \pi r \left(r + \sqrt{r^2+h^2}\right) = \pi r(r + s) \, </math>
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| | ''s'' = slant height of the cone,<br>
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| ''r'' = radius of the circular base,<br>
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| ''h'' = height of the cone
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| |-
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| |[[Pyramid (geometry)|Pyramid]]
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| |<math>B + \frac{PL}{2}</math>
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| |''B'' = area of base, ''P'' = perimeter of base, ''L'' = slant height
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| |-
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| |[[Square pyramid]]
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| |<math> b^2 + 2bs </math>
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| |''b'' = base length, ''s'' = slant height
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| |}
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| ===Ratio of surface areas of a sphere and cylinder of the same Radius and Height===
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| [[Image:Inscribed cone sphere cylinder.svg|thumb|300px|A cone, sphere and cylinder of radius ''r'' and height ''h''.]]
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| The below given formulas can be used to show that the surface area of a [[sphere]] and [[cylinder (geometry)|cylinder]] of the same radius and height are in the ratio '''2 : 3''', as follows.
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| Let the radius be ''r'' and the height be ''h'' (which is 2''r'' for the sphere).
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| <math>\begin{array}{rlll} | |
| \text{Sphere surface area} & = 4 \pi r^2 & & = (2 \pi r^2) \times 2 \\
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| \text{Cylinder surface area} & = 2 \pi r (h + r) & = 2 \pi r (2r + r) & = (2 \pi r^2) \times 3
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| \end{array}</math>
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| The discovery of this ratio is credited to [[Archimedes]].<ref>{{cite web |first=Chris |last=Rorres|url = http://www.math.nyu.edu/~crorres/Archimedes/Tomb/Cicero.html|title = Tomb of Archimedes: Sources|publisher = Courant Institute of Mathematical Sciences|accessdate = 2007-01-02}}</ref>
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| == In chemistry ==
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| {{see also|Accessible surface area}}
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| Surface area is important in [[chemical kinetics]]. Increasing the surface area of a substance generally increases the [[reaction rate|rate]] of a [[chemical reaction]]. For example, [[iron]] in a fine powder will [[combustion|combust]], while in solid blocks it is stable enough to use in structures. For different applications a minimal or maximal surface area may be desired.
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| == In biology ==
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| {{see also|Surface-area-to-volume ratio}}
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| [[Image:Mitochondrion 186.jpg|right|thumb|The inner membrane of the [[mitochondrion]] has a large surface area due to infoldings, allowing higher rates of [[cellular respiration]] (electron [[micrograph]]).]]
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| The surface area of an organism is important in several considerations, such as regulation of body temperature and [[digestion]]. Animals use their [[teeth]] to grind food down into smaller particles, increasing the surface area available for digestion. The epithelial tissue lining the digestive tract contains [[microvilli]], greatly increasing the area available for absorption. [[Elephant]]s have large [[ear]]s, allowing them to regulate their own body temperature. In other instances, animals will need to minimize surface area; for example, people will fold their arms over their chest when cold to minimize heat loss.
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| The [[surface area to volume ratio]] (SA:V) of a [[cell (biology)|cell]] imposes upper limits on size, as the volume increases much faster than does the surface area, thus limiting the rate at which substances diffuse from the interior across the [[cell membrane]] to interstitial spaces or to other cells. Indeed, representing a cell as an idealized [[sphere]] of radius ''r'', the volume and surface area are, respectively, ''V'' = 4/3 π ''r''<sup>3</sup>; ''SA'' = 4 π ''r''<sup>2</sup>. The resulting surface area to volume ratio is therefore 3/''r''. Thus, if a cell has a radius of 1 μm, the SA:V ratio is 3; whereas if the radius of the cell is instead 10 μm, then the SA:V ratio becomes 0.3. With a cell radius of 100, SA:V ratio is 0.03. Thus, the surface area falls off steeply with increasing volume.
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| == References ==
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| <references />
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| * {{eom|title=Area|id=A/a013180|author=Yu.D. Burago, V.A. Zalgaller, L.D. Kudryavtsev}}
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| ==External links==
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| *[http://blog.thinkwell.com/2010/07/6th-grade-math-surface-area.html Surface Area Video] at Thinkwell
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| [[Category:Area]]
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| [[es:Área de superficies]]
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| [[pl:Pole powierzchni]]
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| [[sv:Area]]
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