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Green's Theorem

In this topic:

    (1) State Green's theorem for imply connected regions.
    
    (2) Use Green's theorem to evaluate the line integral greens theorem _gr_1.gif] around the curve greens theorem _gr_2.gif] defined by the ellipse greens theorem _gr_3.gif] oriented counterclockwise.
    
    (3) Use Green's theorem to evaluate the line integral greens theorem _gr_4.gif] around the curve greens theorem _gr_5.gif] defined by the unit circle oriented clockwise.  
    
    (4) Use Green's theorem to evaluate the line integral greens theorem _gr_6.gif] around the curve greens theorem _gr_7.gif] defined by the square with vertices greens theorem _gr_8.gif] greens theorem _gr_9.gif] greens theorem _gr_10.gif] greens theorem _gr_11.gif] oriented counterclockwise.
    
    (5) Find the work done when an object moves in the force field greens theorem _gr_12.gif] once counterclockwise around the circular path greens theorem _gr_13.gif]
    
    (6) Find the work done when an object moves in the force field greens theorem _gr_14.gif] once counterclockwise around the circular path   greens theorem _gr_15.gif]
    

    Green's theorem elegantly yields another technique to evaluate a line integral of a vector field and is especially important when the vector field is not conservative. To do so, Green's theorem assumes that we have a simply connected region that is bounded by a positively oriented piecewise smooth Jordan curve. In this case, Green's theorem offers us a way to evaluate a line integral of a continuously differentiable vector field by computing a double integral involving the partials of the component functions of the vector field. It can be thought of as a generalization of the fundamental theorem of calculus for definite integrals because it gives us a way to evaluate a double integral using only the values of partial antiderivatives on the boundary of the domain of integration.
    Green's theorem for doubly connected regions and alternate forms of Green's theorem involving the curl and div of a vector field are also detailed.

Proposition (Green's Theorem) Let greens theorem _gr_16.gif] be a simply connected region with a piecewise smooth boundary curve greens theorem _gr_17.gif] oriented counterclockwise, greens theorem _gr_18.gif] be a continuously differentiable vector field on greens theorem _gr_19.gif] greens theorem _gr_20.gif] and greens theorem _gr_21.gif] be the tangential and normal components of greens theorem _gr_22.gif] respectively then

greens theorem _gr_23.gif]

and, in vector form,

greens theorem _gr_24.gif]

greens theorem _gr_25.gif]

Example (Green's Theorem) Use Green's theorem to evaluate the line integral greens theorem _gr_26.gif] around the curve greens theorem _gr_27.gif] defined by the ellipse greens theorem _gr_28.gif] oriented counterclockwise.  

    Solution.  Using polar coordinates we have,
    
greens theorem _gr_29.gif]

greens theorem _gr_30.gif]
greens theorem _gr_31.gif]

Example (Green's Theorem) Use Green's theorem to evaluate the line integral greens theorem _gr_32.gif] around the curve greens theorem _gr_33.gif] defined by the unit circle oriented clockwise.  

    Solution. Using polar coordinates we have,
    
greens theorem _gr_34.gif]

greens theorem _gr_35.gif]
greens theorem _gr_36.gif]

Example (Green's Theorem) Use Green's theorem to evaluate the line integral greens theorem _gr_37.gif] around the curve greens theorem _gr_38.gif] defined by the square with vertices greens theorem _gr_39.gif] greens theorem _gr_40.gif] greens theorem _gr_41.gif] greens theorem _gr_42.gif] oriented counterclockwise.

    Solution. We have,
    
greens theorem _gr_43.gif]
greens theorem _gr_44.gif]

Example (Green's Theorem) Find the work done when an object moves in the force field greens theorem _gr_45.gif] once counterclockwise around the circular path greens theorem _gr_46.gif]

    Solution.  We have,  

greens theorem _gr_47.gif]

greens theorem _gr_48.gif]

greens theorem _gr_49.gif]
greens theorem _gr_50.gif]

Example (Green's Theorem) Find the work done when an object moves in the force field greens theorem _gr_51.gif] once counterclockwise around the circular path   greens theorem _gr_52.gif]

    Solution.  We have,

greens theorem _gr_53.gif]

greens theorem _gr_54.gif]

greens theorem _gr_55.gif]

Cite this as:
Greens Theorem
Published by Library of Math -- Online math organized by subject into topics.
Written by Smith, David A.
http://www.libraryofmath.com/greens-theorem.html
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