Multivariable Calculus · 免费预览

保守场与势函数

路径无关性作为保守场的定义性特征,线积分基本定理,以及从梯度场中恢复势函数。

1. The class of fields where paths stop mattering

The class of fields where paths stop mattering

2. A worked potential computation

A worked potential computation

3. Recovering the potential

Recovering the potential

4. Why gradients deserve the name

Why gradients deserve the name

5. The fundamental theorem application

Using V=x2+y2V = x^2 + y^2, what is the work of ∇V\nabla V from (1,0)(1, 0) to (0,1)(0, 1) along any path?

6. Rebuilding a potential

For F=(2xy, x2)\mathbf{F} = (2x y,\ x^2), integrating the first component in xx gives V=x2y+g(y)V = x^2 y + g(y). What comes next?

7. The failure that proves non-conservativeness

Rebuilding a potential for (−y,x)(-y, x) leaves ∂y(−xy+g(y))=−x+g′(y)\partial_y(-xy + g(y)) = -x + g'(y) against the needed xx. What does this prove?

8. Potential of a separated field

For F=(2x, 2y)\mathbf{F} = (2x,\ 2y), give the potential VV with zero constant, in the form a^2+b^2.

9. Work as a potential difference

A field has potential V=sin⁡(xy)V = \sin(xy), and work is computed from (1,0)(1, 0) to (1,π/2)(1, \pi/2). Give the work, as a plain number.

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