Calculus Animations,Graphics and Lecture Notes

Line Integrals

About Kelly Liakos
Calculus 1- Limits and Derivatives
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2 Poems

In Physics1 or Calculus 2 you were introduced to the idea of Work. (See the page on Work if you want a review)

If an object is moving in one-dimension under the influence of a force which is constant in both magnitude and direction then work is defined by Work = Force x Distance.

In Calculus2 you examined the situation when F was not constant in magnitude but was constant in direction. Motion was still in one dimension. This led to an integral formula for work.

However what happens if we have a vector field  F neither constant in magnitude nor direction and a curve in 2 or 3-space defined parametrically by r(t). How do we calculate the work done in this more general setting?

This leads us to the development of the Line Integral also known as the Contour Integral.

In the first download we develop the Line Integral and the following 6 animations illustrate the general situation.

We then present the solutions to the line integrals in the 6 animations followed by further examples.

Before beginning you may want to review the notes on vector fields.

Notes - Vector Fields

Notes - Development of the Line Integral

In the first 3 animations we use the vector field F = -y i + x j.

In the first animation the path is the unit square.

In the second animation the path starts at the origin, The particle moves along the parabola

y = x2 to the point (1,1) then moves back to the origin along  y = x.

In the third animation the path is a triangle with vertices at (0,0), (1,0), and (1/2,1/2).

In the animations 4 through 6 we change the vector field to F = y i + x j  but use the same paths as in the first 3.

Animation 1 - Unit Square

Animation 2 - Parabolic Path

Animation 3 - Triangular Path

Animation 4 - Unit Square

Animation 5 - Parabolic Path

Animation 6 - Triangular Path

Solutions to Animations 1-3

Solutions to Animations 4-6

In the previous examples we proceeded as if the parameterization of a particular curve was unimportant. The following download demonstrates that indeed this is the case.

In this download we also discuss what happens if we reverse the orientation along a given path.

Notes - Independence of Parameterization

Path Independence and Conservative Vector Fields

Green's Theorem

Show that if F is a force field with constant magnitude k pointing outward from the origin


then the work done as a particle travels along the smooth curve y = f(x) as x varies from a to b


is k ((b2 +f(b)2)1/2 - (a2 +f(a)2)1/2)

Solution to Radial Force Problem

A 3-D example using direct computation and Stoke's Thm

Another Example in 3-D with direct computation and Stoke's Theorem

For more examples involving Stokes Theorem  see the page on Flux Integrals

The Smart Bunny-A very short story by Kurt Vonnegut Jr.

©2008-2010 Kelly Liakos

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