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Finding potential functions Determine whether the following vector fields are conservative on the specified region. If so, determine a potential function. Let \(R^{*}\) and \(D^{*}\) be open regions of \(\mathbb{R}^{2}\) and \(\mathbb{R}^{3}\), respectively, that do not include the origin. $$\quad \mathbf{F}=\left\langle x^{3}-x y, \frac{x^{2}}{2}+y\right\rangle \text { on } \mathbb{R}^{2}$$

Short Answer

Expert verified
If so, find its potential function. Answer: No, the vector field is not conservative in \(\mathbb{R}^2\), as its curl is non-zero. Therefore, there is no potential function associated with this vector field.

Step by step solution

01

Calculate the curl of the vector field

To find out whether the given vector field \(\mathbf{F}=\left\langle x^{3}-x y, \frac{x^{2}}{2}+y\right\rangle\) is conservative, we will compute the curl of the vector field in two dimensions. The curl in \(\mathbb{R}^2\) is defined as: $$\nabla \times \mathbf{F} = \frac{\partial F_2}{\partial x} - \frac{\partial F_1}{\partial y}$$ where \(F_1\) is the first component of the vector field and \(F_2\) is the second component.
02

Determine if the vector field is conservative

Now we can compute the curl of the given vector field: $$\nabla \times \mathbf{F} = \frac{\partial}{\partial x}\left(\frac{x^2}{2} + y\right) - \frac{\partial}{\partial y}(x^3 - xy)$$ Calculate the partial derivatives: $$\frac{\partial}{\partial x}\left(\frac{x^2}{2} + y\right) = x$$ $$\frac{\partial}{\partial y}(x^3 - xy) = -x$$ Therefore, the curl of the vector field is: $$\nabla \times \mathbf{F} = x - (-x) = 2x$$ The curl is not zero, which means the given vector field \(\mathbf{F}\) is not conservative on \(\mathbb{R}^2\). As a result, we cannot find a potential function for this vector field.

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Key Concepts

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

Potential Functions
In vector calculus, potential functions play a crucial role in understanding vector fields. A potential function is essentially a scalar function whose gradient is equal to a given vector field. When a vector field is conservative, it has a potential function. This means that there exists a function \( \phi(x, y) \) such that \( abla \phi = \mathbf{F} \). If a vector field has no curl (i.e., the curl is zero), it tends to be conservative and thus admits a potential function.
To find a potential function, you integrate the components of the vector field. However, if the curl is not zero, as in the example given, a potential function does not exist.
This is because the vector field is not conservative. Determining the existence of potential functions helps in simplifying complex vector field problems and aids in solving physical problems like calculating work done by a force field.
Curl in Mathematics
The curl is a fundamental concept in vector calculus that measures the rotation or swirling strength of a vector field. For a vector field \( \mathbf{F} \) in two dimensions, the curl is computed as:\[ abla \times \mathbf{F} = \frac{\partial F_2}{\partial x} - \frac{\partial F_1}{\partial y} \]
In essence, the curl checks if a field is rotating around a point.
  • If the curl is zero everywhere, the vector field is likely conservative.
  • For our exercise, the curl calculated was \( 2x \), thus indicating non-conservativeness since it's not zero.
    This tells us that the field doesn't maintain a constant curl, implying no single potential function for the entire region.
Understanding curl is vital because it indicates the conservativeness of a field, which is crucial for determining other properties like potential functions.
Partial Derivatives
Partial derivatives are derivatives of multivariable functions taken with respect to one variable, keeping others constant. They are essential in vector calculus for analyzing vector fields.
  • When working with vector fields, partial derivatives allow us to find the rate of change of a field component along one direction.
  • In our context, we used partial derivatives to compute the curl of the vector field:
    • \( \frac{\partial F_2}{\partial x} \): Changed along the \( x \)-direction.
    • \( \frac{\partial F_1}{\partial y} \): Changed along the \( y \)-direction.
By determining these derivatives, we identify rotational characteristics of the field. Hence, grasping partial derivatives helps you decode complex behaviors in multivariate scenarios effectively.
Vector Calculus
Vector calculus is a branch of mathematics focused on vector fields and operations like divergence, gradient, and curl. It combines calculus and linear algebra principles to study spatial phenomena:
1. **Gradient**: Converts a scalar function into a vector field.
2. **Divergence**: Measures a vector field's tendency to originate from or converge at a point.
3. **Curl**: Determines the rotation of the vector field, as we calculated earlier.
The example exercise dealt with determining if a vector field is conservative, a typical application of vector calculus.
Understanding vector calculus concepts helps solve diverse physical and geometric problems by analyzing variations and distributions within vector fields, making it a powerful tool in mathematical analysis.

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Most popular questions from this chapter

Prove the following identities. Assume \(\varphi\) is a differentiable scalar- valued function and \(\mathbf{F}\) and \(\mathbf{G}\) are differentiable vector fields, all defined on a region of \(\mathbb{R}^{3}\). $$\nabla \cdot(\mathbf{F} \times \mathbf{G})=\mathbf{G} \cdot(\nabla \times \mathbf{F})-\mathbf{F} \cdot(\nabla \times \mathbf{G})$$

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