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Find curl \((\operatorname{curl} \mathbf{F})=\nabla \times(\nabla \times \mathbf{F})\). \(\mathbf{F}(x, y, z)=x y z \mathbf{i}+y \mathbf{j}+z \mathbf{k}\)

Short Answer

Expert verified
\(\operatorname{curl} \mathbf{F}=0\mathbf{i}-\mathbf{j}+xz\mathbf{k}\)

Step by step solution

01

Define the vector field

Given the vector field \( \mathbf{F}(x, y, z)=x y z \mathbf{i}+y \mathbf{j}+z \mathbf{k}\), the components of the vector field are \(F_1 = xyz, F_2 = y, F_3 = z\).
02

Form the cross product matrix with the Del operator

The curl of a vector field is given by the cross product of the Del operator \( (\partial_x, \partial_y, \partial_z) \) with the vector field. This can be written as determinants of a 3x3 matrix, |\[i, j, k],[\partial_x, \partial_y, \partial_z],[xyz, y, z]\]|.
03

Calculate the determinant

The determinant of the above matrix gives the curl of \(\mathbf{F}\). Using cofactoring, we get \[\operatorname{curl} \mathbf{F}=(\partial_y(z)-\partial_z(y))\mathbf{i}-(\partial_x(z)-\partial_z(xyz))\mathbf{j}+(\partial_x(y)-\partial_y(xyz))\mathbf{k}\].
04

Evaluate the partial derivatives

Substituting the values of the partial derivatives, gives \[\operatorname{curl} \mathbf{F}=0\mathbf{i}-\mathbf{j}+xz\mathbf{k}\].

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Key Concepts

These are the key concepts you need to understand to accurately answer the question.

Cross Product
Understanding the cross product is fundamental when dealing with the curl of a vector field. The cross product, also known as the vector product, is a binary operation on two vectors in three-dimensional space. It results in a third vector which is perpendicular to the plane containing the original vectors. The magnitude of this vector is proportional to the area of the parallelogram formed by the initial vectors.

The cross product of vectors \textbf{A} and \textbf{B} is denoted as \textbf{A} \times \textbf{B}. The formula for the cross product is defined as:\[\textbf{A} \times \textbf{B} = (A_yB_z - A_zB_y)\textbf{i} + (A_zB_x - A_xB_z)\textbf{j} + (A_xB_y - A_yB_x)\textbf{k}\]where \textbf{i}, \textbf{j}, and \textbf{k} are the unit vectors along the x, y, and z axes, respectively. In terms of curl, which involves the cross product of the Del operator with a vector field, the result expresses the rotation tendency at a point in the vector field.
Del Operator
Often represented by the nabla symbol (\( abla \)), the Del operator is a vector differential operator used extensively in vector calculus. Specifically, the Del operator is defined as:\[abla = \frac{\partial}{\partial x}\textbf{i} + \frac{\partial}{\partial y}\textbf{j} + \frac{\partial}{\partial z}\textbf{k}\]The operator combines the partial derivative operations with respect to each spatial dimension into a vector form. This compact notation allows for the expression of various types of differentiation including gradient, divergence, and curl of a vector field.

Application to Curl

The curl of a vector field, in this case, is expressed as the cross product of the Del operator with the given vector field, symbolically represented as \( abla \times \mathbf{F} \). The computation involves taking the symbolic cross product resulting in a determinant that, once resolved, yields the curl.
Partial Derivatives
Partial derivatives play a critical role in describing the rate at which a function changes as each variable is varied independently, while treating other variables as constants. When computing the curl of a vector field, we examine the rate of change of the field components with respect to each corresponding axis.To find the curl, as seen in the exercise, it is necessary to evaluate the partial derivatives of the vector field's components. For example, the partial derivative of a component function \( f(x, y, z) \) with respect to \( x \) is denoted by \( \frac{\partial f}{\partial x} \). In physical terms, these derivatives help to detect the presence of rotational effects within a vector field, which is important for understanding fluid dynamics and electromagnetic fields among other applications.
Vector Field
A vector field is a mathematical construct which assigns a vector to every point in a subset of space. These vectors can represent a variety of physical quantities, such as velocity, force, or electric or magnetic fields. A vector field in three dimensions is typically written as \( \mathbf{F}(x, y, z) = F_x\textbf{i} + F_y\textbf{j} + F_z\textbf{k} \), where \( F_x, F_y, \) and \( F_z \) are the component functions that depend on the coordinates \( x, y, \) and \( z \).

Visualization and Physical Interpretation

Visualizing a vector field can be done by sketching the vectors at a selection of points in the space, typically resulting in a flow-like pattern. These patterns can convey information about the behavior of a physical system, such as the flow of fluids or the intensity and direction of forces. The curl operation we discuss in this context helps to understand rotational or swirling motions within a vector field, enabling deeper insight into the dynamics of the system it represents.

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Most popular questions from this chapter

Moment of Inertia, find \(I_{z}\) for the given lamina with uniform density of 1. Use a computer algebra system to verify your results. \(x^{2}+y^{2}=a^{2}, \quad 0 \leq z \leq h\)

The motion of a liquid in a cylindrical container of radius 1 is described by the velocity field \(\mathbf{F}(x, y, z)\). Find $$\int_{S} \int(\operatorname{curl} \mathbf{F}) \cdot \mathbf{N} d S$$ where \(S\) is the upper surface of the cylindrical container. \(\mathbf{F}(x, y, z)=-z \mathbf{i}+y \mathbf{k}\)

(a) Use a computer algebra system to graph the vector-valued function \(\mathbf{r}(u, v)=(4-v \sin u) \cos (2 u) \mathbf{i}+(4-v \sin u) \sin (2 u) \mathbf{j}+\) \(v \cos u \mathbf{k}, \quad 0 \leq u \leq \pi, \quad-1 \leq v \leq 1 .\) This surface is called a Möbius strip. (b) Explain why this surface is not orientable. (c) Use a computer algebra system to graph the space curve represented by \(\mathbf{r}(u, 0)\). Identify the curve. (d) Construct a Möbius strip by cutting a strip of paper, making a single twist, and pasting the ends together. (e) Cut the Möbius strip along the space curve graphed in part (c), and describe the result.

Find the area of the surface over the given region. Use a computer algebra system to verify your results. $$ \begin{aligned} &\text { The part of the paraboloid } \mathbf{r}(u, v)=4 u \cos v \mathbf{i}+4 u \sin v \mathbf{j}+\\\ &u^{2} \mathbf{k} \text { , where } 0 \leq u \leq 2 \text { and } 0 \leq v \leq 2 \pi \end{aligned} $$

Möbius Strip The surface shown in the figure is called a Möbius Strip and can be represented by the parametric equations \(x=\left(a+u \cos \frac{v}{2}\right) \cos v, y=\left(a+u \cos \frac{v}{2}\right) \sin v, z=u \sin \frac{v}{2}\) where \(-1 \leq u \leq 1,0 \leq v \leq 2 \pi\), and \(a=3 .\) Try to graph other Möbius strips for different values of \(a\) using a computer algebra system.

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