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## Main Question or Discussion Point

what is meant by the term 'surface term'?

thank you

thank you

- Thread starter Ratzinger
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what is meant by the term 'surface term'?

thank you

thank you

HallsofIvy

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I thought it is a household (mathematical) term, because I remember the author used it without further explaining.

Have to note that my math and physics skills are not too advanced, can deal with upper undergraduate physics texts, but have hard times with more. (Especially when they throw in terms and equations from out of nowhere.)

lurflurf

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Usually a surface term is a term that results from integration over the boundry of some region. Them a bulk or volume term results from integrating over the region. Surface and boundry terms are related by stokes theorem and by conservation laws. A common example is a surface term equal to the flux of some quantity through the boundry of a surface equals the rate of change in the amount of the quantity inside the surface. It might help to think of the 1-D situation

[tex]\frac{d}{dt}\int_{a(t)}^{b(t)} f(x,t) dt=\int_{a(t)}^{b(t)} \frac{\partial}{\partial t}f(x,t)dx+f(x,t)\frac{\partial x}{\partial t}\displaystyle{|_{x=a(t)}^{x=b(t)}}[/tex]

So in 1-D integrals are bulk terms and differences are surface terms. Often in applications the bulk terms are integrals over 3-D regions and surface terms are integrals over 2-D boundries of 3-D regions.

[tex]\frac{d}{dt}\int_{a(t)}^{b(t)} f(x,t) dt=\int_{a(t)}^{b(t)} \frac{\partial}{\partial t}f(x,t)dx+f(x,t)\frac{\partial x}{\partial t}\displaystyle{|_{x=a(t)}^{x=b(t)}}[/tex]

So in 1-D integrals are bulk terms and differences are surface terms. Often in applications the bulk terms are integrals over 3-D regions and surface terms are integrals over 2-D boundries of 3-D regions.

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thanks lurflurf...why aren't you science adviser or homework helper yet?

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∫

in which case the first term on the right is called the "surface term".

EnumaElish

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This is off the subject, but -- PBRMEASAP, how did you make the math notation without tex?

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right click on the eq and view source.

EnumaElish

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Does that mean I need to type character string &-#-8-7-4-7 (without the dashes) to make the ∫ sign?

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without the spaces gives ∫

I haven't figured out how to make the superscript go directly over the subscript. You can also make greek letters:

& alpha ;

& beta ;

& gamma ;

gives

α, β, γ, etc.

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