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
around the curve
defined by the ellipse
oriented counterclockwise. (3) Use Green's theorem to evaluate the line integral
around the curve
defined by the unit circle oriented clockwise. (4) Use Green's theorem to evaluate the line integral
around the curve
defined by the square with vertices
oriented counterclockwise. (5) Find the work done when an object moves in the force field
once counterclockwise around the circular path
![greens theorem _gr_13.gif]](pages/greens-theorem/Images/greens-theorem_gr_13.gif) (6) Find the work done when an object moves in the force field
once counterclockwise around the circular path
![greens theorem _gr_15.gif]](pages/greens-theorem/Images/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
be a simply connected region with a piecewise smooth boundary curve
oriented counterclockwise,
be a continuously differentiable vector field on
and
be the tangential and normal components of
respectively then
![greens theorem _gr_23.gif]](pages/greens-theorem/Images/greens-theorem_gr_23.gif)
and, in vector form,
![greens theorem _gr_24.gif]](pages/greens-theorem/Images/greens-theorem_gr_24.gif)
Example (Green's Theorem) Use Green's theorem to evaluate the line integral
around the curve
defined by the ellipse
oriented counterclockwise.
Solution. Using polar coordinates we have,
![greens theorem _gr_29.gif]](pages/greens-theorem/Images/greens-theorem_gr_29.gif)
![greens theorem _gr_30.gif]](pages/greens-theorem/Images/greens-theorem_gr_30.gif)
![greens theorem _gr_31.gif]](pages/greens-theorem/Images/greens-theorem_gr_31.gif)
Example (Green's Theorem) Use Green's theorem to evaluate the line integral
around the curve
defined by the unit circle oriented clockwise.
Solution. Using polar coordinates we have,
![greens theorem _gr_34.gif]](pages/greens-theorem/Images/greens-theorem_gr_34.gif)
![greens theorem _gr_35.gif]](pages/greens-theorem/Images/greens-theorem_gr_35.gif)
![greens theorem _gr_36.gif]](pages/greens-theorem/Images/greens-theorem_gr_36.gif)
Example (Green's Theorem) Use Green's theorem to evaluate the line integral
around the curve
defined by the square with vertices
oriented counterclockwise.
Solution. We have,
![greens theorem _gr_43.gif]](pages/greens-theorem/Images/greens-theorem_gr_43.gif)
![greens theorem _gr_44.gif]](pages/greens-theorem/Images/greens-theorem_gr_44.gif)
Example (Green's Theorem) Find the work done when an object moves in the force field
once counterclockwise around the circular path
![greens theorem _gr_46.gif]](pages/greens-theorem/Images/greens-theorem_gr_46.gif)
Solution. We have,
![greens theorem _gr_47.gif]](pages/greens-theorem/Images/greens-theorem_gr_47.gif)
![greens theorem _gr_48.gif]](pages/greens-theorem/Images/greens-theorem_gr_48.gif)
![greens theorem _gr_49.gif]](pages/greens-theorem/Images/greens-theorem_gr_49.gif)
![greens theorem _gr_50.gif]](pages/greens-theorem/Images/greens-theorem_gr_50.gif)
Example (Green's Theorem) Find the work done when an object moves in the force field
once counterclockwise around the circular path
![greens theorem _gr_52.gif]](pages/greens-theorem/Images/greens-theorem_gr_52.gif)
Solution. We have,
![greens theorem _gr_53.gif]](pages/greens-theorem/Images/greens-theorem_gr_53.gif)
![greens theorem _gr_54.gif]](pages/greens-theorem/Images/greens-theorem_gr_54.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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