Chapter 14: Problem 5
Interpret the curl of a general rotation vector field.
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Chapter 14: Problem 5
Interpret the curl of a general rotation vector field.
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Prove Green's Second Identity for scalar-valued functions \(u\) and \(v\) defined on a region \(D\) : $$\iiint_{D}\left(u \nabla^{2} v-v \nabla^{2} u\right) d V=\iint_{S}(u \nabla v-v \nabla u) \cdot \mathbf{n} d S$$ (Hint: Reverse the roles of \(u\) and \(v\) in Green's First Identity.)
The area of a region \(R\) in the plane, whose boundary is the closed curve \(C,\) may be computed using line integrals with the formula $$\text { area of } R=\int_{C} x d y=-\int_{C} y d x$$ These ideas reappear later in the chapter. Let \(R=\\{(r, \theta): 0 \leq r \leq a, 0 \leq \theta \leq 2 \pi\\}\) be the disk of radius \(a\) centered at the origin and let \(C\) be the boundary of \(R\) oriented counterclockwise. Use the formula \(A=-\int_{C} y d x\) to verify that the area of the disk is \(\pi r^{2}.\)
Generalize Exercise 43 to show that the rotation field \(\mathbf{F}=\mathbf{a} \times \mathbf{r}\) circles the vector a in the counterclockwise direction looking along a from head to tail.
Explain why or why not Determine whether the following statements are true and give an explanation or counterexample. a. A paddle wheel with its axis in the direction \langle 0,1,-1\rangle would not spin when put in the vector field $$ \mathbf{F}=\langle 1,1,2\rangle \times\langle x, y, z\rangle $$ b. Stokes' Theorem relates the flux of a vector field \(\mathbf{F}\) across a surface to the values of \(\mathbf{F}\) on the boundary of the surface. c. A vector field of the form \(\mathbf{F}=\langle a+f(x), b+g(y)\) \(c+h(z)\rangle,\) where \(a, b,\) and \(c\) are constants, has zero circulation on a closed curve. d. If a vector field has zero circulation on all simple closed smooth curves \(C\) in a region \(D,\) then \(\mathbf{F}\) is conservative on \(D\)
Use the procedure in Exercise 57 to construct potential functions for the following fields. $$\mathbf{F}=\left\langle 2 x^{3}+x y^{2}, 2 y^{3}+x^{2} y\right\rangle$$
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