Chapter 14: Problem 3
How do you graph the vector field \(\mathbf{F}=\langle f(x, y), g(x, y)\rangle ?\)
Chapter 14: Problem 3
How do you graph the vector field \(\mathbf{F}=\langle f(x, y), g(x, y)\rangle ?\)
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Get started for freeFor what vectors \(\mathbf{n}\) is \((\operatorname{curl} \mathbf{F}) \cdot \mathbf{n}=0\) when \(\mathbf{F}=\langle y,-2 z,-x\rangle ?\)
Use Stokes' Theorem to write the circulation form of Green's Theorem in the \(y z\) -plane.
Write Gauss' Formula of Exercise 48 in two dimensions- -that is, where \(\mathbf{F}=\langle f, g\rangle, D\) is a plane region \(R\) and \(C\) is the boundary of \(R .\) Show that the result is Green's Formula: $$\iint_{R} u\left(f_{x}+g_{y}\right) d A=\oint u(\mathbf{F} \cdot \mathbf{n}) d s-\iint_{R}\left(f u_{x}+g u_{y}\right) d A$$ Show that with \(u=1,\) one form of Green's Theorem appears. Which form of Green's Theorem is it?
Suppose an object with mass \(m\) moves in a region \(R\) in a conservative force field given by \(\mathbf{F}=-\nabla \varphi\) where \(\varphi\) is a potential function in a region \(R .\) The motion of the object is governed by Newton's Second Law of Motion, \(\mathbf{F}=m \mathbf{a}\) where a is the acceleration. Suppose the object moves from point \(A\) to point \(B\) in \(R\). a. Show that the equation of motion is \(m \frac{d \mathbf{v}}{d t}=-\nabla \varphi\) b. Show that \(\frac{d \mathbf{v}}{d t} \cdot \mathbf{v}=\frac{1}{2} \frac{d}{d t}(\mathbf{v} \cdot \mathbf{v})\) c. Take the dot product of both sides of the equation in part (a) with \(\mathbf{v}(t)=\mathbf{r}^{\prime}(t)\) and integrate along a curve between \(A\) and \(B\). Use part (b) and the fact that \(\mathbf{F}\) is conservative to show that the total energy (kinetic plus potential) \(\frac{1}{2} m|\mathbf{v}|^{2}+\varphi\) is the same at \(A\) and \(B\). Conclude that because \(A\) and \(B\) are arbitrary, energy is conserved in \(R\)
Consider the radial field \(\mathbf{F}=\mathbf{r} /|\mathbf{r}|^{p}\) where \(\mathbf{r}=\langle x, y, z\rangle\) and \(p\) is a real number. Let \(S\) be the sphere of radius \(a\) centered at the origin. Show that the outward flux of \(\mathbf{F}\) across the sphere is \(4 \pi / a^{p-3} .\) It is instructive to do the calculation using both an explicit and parametric description of the sphere.
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