Chapter 9: Problem 7
Determine whether the vector field \(\mathbf{F}\) is conservative. If it is, find a potential function for it. If not, explain why not. \(\mathbf{F}(x, y, z)=(x+y z, y+x z, z+x y)\)
Short Answer
Expert verified
The field is conservative; its potential function is \( f(x, y, z) = \frac{x^2}{2} + \frac{y^2}{2} + \frac{z^2}{2} + xyz \).
Step by step solution
01
Check the Curl of the Vector Field
A vector field \( \mathbf{F} \) is conservative if its curl is zero everywhere in the domain. The curl of a vector field \( \mathbf{F}(x, y, z) = (F_1, F_2, F_3) \) is given by:\[ abla \times \mathbf{F} = \left( \frac{\partial F_3}{\partial y} - \frac{\partial F_2}{\partial z}, \frac{\partial F_1}{\partial z} - \frac{\partial F_3}{\partial x}, \frac{\partial F_2}{\partial x} - \frac{\partial F_1}{\partial y} \right) \]Substitute \( F_1 = x + yz, \; F_2 = y + xz, \; F_3 = z + xy \):- \( \frac{\partial F_3}{\partial y} = x \),- \( \frac{\partial F_2}{\partial z} = x \),- \( \frac{\partial F_1}{\partial z} = y \),- \( \frac{\partial F_3}{\partial x} = y \),- \( \frac{\partial F_2}{\partial x} = z \),- \( \frac{\partial F_1}{\partial y} = z \).Thus, \( abla \times \mathbf{F} = (x - x, y - y, z - z) = (0, 0, 0) \).\(\mathbf{F}\) is conservative.
02
Determine the Potential Function
Since \(\mathbf{F}\) is conservative, it has a potential function \( f(x, y, z) \) such that \( abla f = \mathbf{F} \).To find \( f \), integrate the components of \( \mathbf{F} \):1. Integrate \( F_1 = x + yz \) with respect to \( x \): \[ f(x, y, z) = \int (x + yz) \; dx = \frac{x^2}{2} + xyz + g(y, z) \]2. Integrate \( F_2 = y + xz \) with respect to \( y \): \[ f(x, y, z) = \int (y + xz) \; dy = \frac{y^2}{2} + xyz + h(x, z) \]3. Integrate \( F_3 = z + xy \) with respect to \( z \): \[ f(x, y, z) = \int (z + xy) \; dz = \frac{z^2}{2} + xyz + p(x, y) \]Combine these partial results:\[ f(x, y, z) = \frac{x^2}{2} + \frac{y^2}{2} + \frac{z^2}{2} + xyz + C \]where \(C\) is a constant, which can be eliminated in a gradient operation as it does not affect the vector field.
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Key Concepts
These are the key concepts you need to understand to accurately answer the question.
Potential Function
A potential function is a scalar function whose gradient yields a given vector field. In simpler terms, if you have a conservative vector field, you can "uncover" a potential function that essentially "produces" that field by taking its gradient.
A vector field is considered conservative if there exists a potential function, denoted here as \( f(x, y, z) \). For a vector field \(\mathbf{F}\) expressed in terms of its components \( (F_1, F_2, F_3) \), finding this potential function involves these steps:
A vector field is considered conservative if there exists a potential function, denoted here as \( f(x, y, z) \). For a vector field \(\mathbf{F}\) expressed in terms of its components \( (F_1, F_2, F_3) \), finding this potential function involves these steps:
- Identify components of \(\mathbf{F}\)
- Integrate each component with respect to its respective variable
- Combine results, ensuring it forms one consistent function including undetermined functions of the other variables
Curl of a Vector Field
The curl of a vector field helps in determining whether a field is conservative. Mathematically, curl measures the rotational effect at any point within the field.
The curl of a vector field \( \mathbf{F} = (F_1, F_2, F_3) \) is calculated using the formula:
\[abla \times \mathbf{F} = \left( \frac{\partial F_3}{\partial y} - \frac{\partial F_2}{\partial z}, \frac{\partial F_1}{\partial z} - \frac{\partial F_3}{\partial x}, \frac{\partial F_2}{\partial x} - \frac{\partial F_1}{\partial y} \right)\]If the curl is zero throughout its entire domain, the field is conservative, implying the presence of a potential function. The vector field \(\mathbf{F}(x, y, z) = (x + yz, y + xz, z + xy)\) was checked as follows:
The curl of a vector field \( \mathbf{F} = (F_1, F_2, F_3) \) is calculated using the formula:
\[abla \times \mathbf{F} = \left( \frac{\partial F_3}{\partial y} - \frac{\partial F_2}{\partial z}, \frac{\partial F_1}{\partial z} - \frac{\partial F_3}{\partial x}, \frac{\partial F_2}{\partial x} - \frac{\partial F_1}{\partial y} \right)\]If the curl is zero throughout its entire domain, the field is conservative, implying the presence of a potential function. The vector field \(\mathbf{F}(x, y, z) = (x + yz, y + xz, z + xy)\) was checked as follows:
- \( \frac{\partial F_3}{\partial y} = x \) and \( \frac{\partial F_2}{\partial z} = x \)
- \( \frac{\partial F_1}{\partial z} = y \) and \( \frac{\partial F_3}{\partial x} = y \)
- \( \frac{\partial F_2}{\partial x} = z \) and \( \frac{\partial F_1}{\partial y} = z \)
Integration of Vector Components
Integration of vector components is key in determining the potential function of a conservative vector field. Each component of the vector field \( (F_1, F_2, F_3) \) needs to be integrated separately.
For the vector field \( \mathbf{F}(x, y, z) = (x + yz, y + xz, z + xy) \), the integration is performed as follows:
For the vector field \( \mathbf{F}(x, y, z) = (x + yz, y + xz, z + xy) \), the integration is performed as follows:
- Integrate \( F_1 = x + yz \) with respect to \( x \) results in: \[ f(x, y, z) = \int (x + yz) \, dx = \frac{x^2}{2} + xyz + g(y, z) \]
- Integrate \( F_2 = y + xz \) with respect to \( y \) results in: \[ f(x, y, z) = \int (y + xz) \, dy = \frac{y^2}{2} + xyz + h(x, z) \]
- Integrate \( F_3 = z + xy \) with respect to \( z \) results in: \[ f(x, y, z) = \int (z + xy) \, dz = \frac{z^2}{2} + xyz + p(x, y) \]