What is Line integrals: Definition and 130 Discussions

In mathematics, a line integral is an integral where the function to be integrated is evaluated along a curve. The terms path integral, curve integral, and curvilinear integral are also used; contour integral is used as well, although that is typically reserved for line integrals in the complex plane.
The function to be integrated may be a scalar field or a vector field. The value of the line integral is the sum of values of the field at all points on the curve, weighted by some scalar function on the curve (commonly arc length or, for a vector field, the scalar product of the vector field with a differential vector in the curve). This weighting distinguishes the line integral from simpler integrals defined on intervals. Many simple formulae in physics, such as the definition of work as



W
=

F



s



{\displaystyle W=\mathbf {F} \cdot \mathbf {s} }
, have natural continuous analogues in terms of line integrals, in this case




W
=



L



F

(

s

)

d

s




{\displaystyle \textstyle W=\int _{L}\mathbf {F} (\mathbf {s} )\cdot d\mathbf {s} }
, which computes the work done on an object moving through an electric or gravitational field F along a path



L


{\displaystyle L}
.

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  1. G

    Evaluating Line Integrals with Green's Theorem

    Homework Statement Let C be the boundary of the region bounded by the curves y=x^{2} and y=x. Assuming C is oriented counter clockwise, Use green's theorem to evaluate the following line integrals (a) \oint(6xy-y^2)dx and (b) \oint(6xy-y^2)dyHomework Equations The Attempt at a Solution...
  2. 1

    How bad is this statement regarding the Fundamental Theorem for Line Integrals?

    State the Fundamental Theorem: Let F be a vector field. If there exists a function f such that F = grad f, then \int_{C} F \cdot dr = f(Q) - f(P) where P and Q are endpoints of curve C. _________________________________ I didn't receive any credit for this answer. Admittedly...
  3. A

    Fundamental Theorem for Line Integrals

    Vector field F(bar)= <6x+2y,2x+5y> fx(x,y)= 6x+2y fy(x,y)= 2x+5y f(x,y)= 3x^2+2xy+g(y) fy(x,y)=2x+g'(y) 2x+g'(y)= 2x+5y g'(y)= 5y g(y)= 5/2*y^2 f(x,y)=3x^2+2xy+(5/2)y^2 Then find the \int F(bar)*dr(bar) along curve C t^2i+t^3j, 0<t<1 I'm stuck on finding the last part for the F(bar)...
  4. W

    Applications of Line integrals

    other than the physics (work) what are the applications of line integral? particularly does it have any use in finance or economics?
  5. A

    Line integrals and paths with the same endpoints

    Homework Statement Suppose that p and q are points in U, where U is an open, path-connected, simply connected subset of Rn and c1 and c2 are smooth curves in Rn with c1(0)=c2(0)=p, c1(1)=c2(1)=q. Let w be a 1-form on U. Prove that the line integral of w over c1 equals the line integral of w...
  6. B

    Confusion over line integrals, Green's Theoreom, Conservative fields

    Folks, 1) If we have \int F \cdot dr that is independent of the path, does that mean that the integral will always be 0? 2) For 2 dimensional problems when we evaluate line integrals directly and use Greens Theorem for every piece wise smooth closed curves C, arent we always calculating...
  7. B

    Line Integrals 2: Evaluate Triangle on Vertices (0,0), (3,3), (0,3)

    Homework Statement Evaluate this integral directly Homework Equations \int cos x sin y dx +sin x cos y dy on vertices (0,0), (3,3) and (0,3) for a triangle The Attempt at a Solution Does this have to evaluated parametrically using r(t)=(1-t)r_0+tr_1 for 0 \le t\le 1 or can I just...
  8. G

    Solving Non-Conservative Vector Field Line Integrals

    Hi, I'm studying calculus 3 and am currently learning about conservative vector fields. ============================= Fundamental Theorem for Line Integrals ============================= Let F be a a continuous vector field on an open connected region R in ℝ^{2} (or D in ℝ^{3}). There exists...
  9. W

    Conceptual Questions on Line Integrals

    So we have 4 things: -Scalar Line Integral -integral of f(c(t))||c'(t)||dt from b to a -length of C: integral on curve C of ||c'(t)||dt -Vector Line Integral -integral of F(c(t))●c'(t)dt from b to a -Scalar Surface Integral -surface integral: double integral of f(Φ(u,v))||n(u,v)||dudv on...
  10. S

    Line integrals and vector fields.

    Homework Statement There is a circle of equation x^2+y^2=1 and a vector field F (x; y) =< y + .5x, x + .3y >. Imagine the field zoomed in extremely close at (0,1), to the point where it looks like a constant field of <-1,.3>. Calculate the work from say (0,1) to (-.001, 1). The constant field...
  11. J

    Complex Analysis, Line Integrals and Cauchy Conceptually

    I am just trying to get the conceptual basics in my head. Can I think of things this way... If you are taking the integral of a function f(z) along a curve γ in a region A. If the curve is closed and f(z) is analytic on the entire curve as well as everywhere inside the curve, then the...
  12. W

    Understanding the Relationship Between Surface & Line Integrals

    hi experts as far I know the stokes theorem relates surface integral to line integral - but i am confuse how surface integral if represent area gets equal to length as represented by line integral.
  13. T

    Complex Analysis: Properties of Line Integrals

    Homework Statement Demonstrate that \int_{-\gamma} f(z)|dz|=\int_{\gamma} f(z)|dz| where \gamma is a piecewise smooth path and f is a function that is continuous on |\gamma|. Homework Equations The Attempt at a Solution This proof seems like it should be very simple, but I am...
  14. T

    Complex Analysis: Line Integrals

    Homework Statement I have a problem as follows: Let \gamma=\beta+[e^2\pi,1] where \beta is given by \beta(t)=e^{t+it} for 0\leq 2 \leq \pi. Evaluate \int_\gamma z^{-1} dz . Homework Equations The Attempt at a Solution I know that I need to parameterize the path and I have...
  15. J

    Warmup problem for line integrals of conservative force

    Homework Statement A sleeve of mass m is constrained to move without friction along the x-axis. The sleeve is connected to the point (0, 2) on the y-axis by a spring as shown in the diagram below. Assume that Hooke’s “Law” is a good approximation for the restoring force exerted by the...
  16. Y

    Line integrals distance elements

    in line integrals we always need a vector element of distance. I can't understand the difference between ds and dr. is ds for all kinds of paths (even curly ones) and dr only for straight lines, or theyre the same? I am confused, or maybe dr is just the magnitude of ds, and the vector here is...
  17. I

    Quick help with line integrals

    Homework Statement \int_{C}(x+yz)dx + 2xdy + xyzdz C goes from (1,0,1) to (2,3,1) and (2,3,1) to (2,5,2) The Attempt at a Solution For C going from (1,0,1) to (2,3,1) x=1+t, y=3t, z=1; 0\leq t \leq 1 x'(t)=1, y'(t)=3, z'(t)=0 \int^{1}_{0}(1+t+3t)*1dt + 2(1+t)*3dt + 0...
  18. T

    What is the potential function for a line integral with a vector field?

    Homework Statement I have to calculate the following line integral \int_{\gamma}y^{2}cos(xy^{2})dx + 2xycos(xy^{2})dy where \gamma is the path defined by the equations x(t) = t^{4} and y(t)=sin^{3}(\frac{t\pi}{2}) t between 0 and 1Homework Equations Now I know that the formula for calculating...
  19. M

    Fundamental Theorem of Line Integrals

    If someone could link me to a tutorial on how to put in functions into a post, I would appreciate it, thanks. I am going to be putting in screen shots. Homework Statement http://img864.imageshack.us/img864/1517/scr1305133657.png" http://img864.imageshack.us/img864/1517/scr1305133657.png...
  20. L

    Matlab question: line integrals, v-fields

    Homework Statement Evaluate the line integral yzdx+yzdy+ydz where C is the following semicircle The top half of y^2 + z^2 = 4 in the yz plane traveling from left to right. Homework Equations The Attempt at a Solution What I tried, but I know it's not right, and I'm just not sure...
  21. F

    Closed curves and Line Integrals

    Homework Statement Given \mathbf{F} = \nabla f\; where \;f(x,y) = sin(x-2y) Find a curve C that is not closed and satisfy the equation \int_C \mathbf{F}\cdot dr = 0The Attempt at a Solution \nabla f = \;<cos(x - 2y),-2cos(x-2y)> So to satisfy the dot product being 0 (I am hoping I can do...
  22. C

    Computing Line Integrals Related to Vector Field F in R2

    We are given a vector field: F=\frac{-y}{x^2+y^2} , \frac{x}{x^2+y^2} Then asked if F is conservative on R2 \ (0,0). I just solved the partial derivatives of each part of the vector field and they did indeed equal each other, but I don't under stand what the "\(0,0)" part means. We are then...
  23. L

    Solving Complex Line Integrals: Line Segment from 2 to 3+i Using Green's Theorem

    Homework Statement Compute the following line integral: \int_{\gamma} |z|^2 dz where \gamma(t) is the line segment from 2 to 3 + i Homework Equations Green's Theorem The Attempt at a Solution I originally started by saying that y = x - 2 and subing that into the equation "x^2 + y^2"...
  24. B

    Path integral and line integrals

    Homework Statement what is the difference between path integral and line integral? Homework Equations n/a The Attempt at a Solution is path integral over a scalar function and line integral is over vector function? I'm confused about this pls help me understand thanks...
  25. N

    The fundmental thereom of line integrals

    show that the line integral is indpendant of path and evaluate the integral on interval (0,1),(1,2) int c 1-ye^{-x}dx+e^{-x}dy can somone show me the procedure here looks like they just integrated 1-ye^(-x) on x to get 2/e I get a diffrent answer if I integrate e^(-x) on y same interval do I...
  26. B

    Line Integrals of piecewise curves to find mass of wire

    Homework Statement A wire lies along the piecewise linear curve extending from the point (4,3) to the point (6,15) to the point (12,15). If the density of the wire is given by (xy)=3xy+2y, use a line integral to find the mass of the wire. Homework Equations The Attempt at a Solution...
  27. J

    Conservative force fields and line integrals

    Conservative vector fields and line integrals Homework Statement A particle is subject to a force F defined by F\left( x,y \right)=\left(\begin{array}{c} y^{2} \\ 2xy \end{array}\right). The particle moves in a straight line C from (-1,2) to (1,3).[a] Calculate the work done by the force F as...
  28. T

    Question involving fundamental theorem of line integrals

    Homework Statement a) Use the fundamental theorem of line integrals to evaluate the line integral: ∫(2x/(x^2+y^2)^2)dx+(2y/(x^2+y^2)^2)dy (over C) Where C is the arc of the circle (x-4)^2+(y-5)^2=25 taken clockwise from (7,9) to (0,2). Explain why the fundamental theorem can be applied. b)...
  29. T

    Evaluating line integrals versus Green's Theorem

    Homework Statement Find the simple closed integral of (x+xy-y)(dx+dy) counterclockwise around the path of straight line segments from the origin to (0,1) to (1,0) to the origin... a)as a line integral b)using green's theorem Homework Equations Eq of line segment r(t)=(1-t)r0+tr1 Greens...
  30. J

    Conceptual question: Green's Theorem and Line Integrals

    Alright, I have a conceptual question regarding Green's Theorem that I'm hoping someone here can explain. We recently learned in my college class that, by Green's Theorem, if C is a positively-oriented, piecewise-smooth, simple closed curve in the plane and D is the region bounded by C, then the...
  31. J

    Evaluating Line Integrals Using Stokes' Theorem

    Homework Statement Evaluate the line integral I = (x2z + yzexy) dx + xzexy dy + exy dz where C is the arc of the ellipse r(t) = (cost,sint,2−sint) for 0 <= t <= PI. [Hint: Do not compute this integral directly. Find a suitable surface S such that C is a part of the boundary ∂S and use...
  32. H

    Center of Mass via Scalar Line Integrals

    Homework Statement A thin wire has the shape of the first quadrant part of the circle with center at the origin and radius a. If the density function is rho(x,y)=kxy, find the mass and center of mass of the wire. Homework Equations My parametric equation of the circle was x=a*cos(t) and...
  33. L

    Fundamental Theorem of Calculus and Line Integrals: Does it Apply?

    If I draw a random curve over a scalar field, then it is not generally true that the line integral of the scalar field over the curve equals the difference between the value of the antiderivatives of the scalar field at the beginning and finishing points of the curve, as one can clearly see by...
  34. F

    Parameterizing a curve (line integrals)

    Homework Statement I have a vector valued function that I need to integrate over a curve C (which I know how to do). I need to create a vector valued function r(t) for any position on the curve C (see the picture). r(t) is a defined area in the XY-plane and I'm pretty sure it needs a...
  35. R

    Line Integrals / Conservative Vector Fields

    Homework Statement F = < z^2/x, z^2/y, 2zlog(xy)> F = \nabla f, where f = z^2log(xy) Homework Equations Evaluate \int F \cdot ds for any path c from P = (1/2, 4, 2) to Q = (2, 3, 3) contained in the region x > 0, y > 0, z > 0 Why is it necessary to specify that the path lie in the...
  36. L

    I saw somewhere triple line integrals

    I saw somewhere triple line integrals, 3 integrals with a circle(the symbol) , may you tell me exactly what are called, to find & study them ?
  37. J

    Line Integrals: Gradient Field and Calculations for -2,0 to 2,0 Points

    Homework Statement F = (3x2 + 2y cos(xy))i + (2y + 2x cos(xy))j a - show that F is a gradient field b - calculate the integral of F dot dr where c includes the points -2,0 and 2,0 c - determine the value of the integral of F dot dr where c is any curve joining -2,0 and 2,0...
  38. D

    Solving Line Integrals: A Puzzling Problem

    Homework Statement \int _c{(x^2 + y + \sqrt{x})dx + (y - x^2 + \sin{y}) dy Homework Equations The Attempt at a Solution I'm not sure which theorem to use here. Do I use Green's or the Divergence? Even once I get past this I'm not sure that I can get started.
  39. B

    Parametrizing and Line integrals (of a line, parabola, curve.)

    Homework Statement In each part, evaluate the integral \int(3x+2y)dx+(2x-y)dy (A) The line segment from (0,0) to (1,1). (b) The parabolic arc y=x^2 (c) The curve y=sin(pi(x)/2) from (0,0) to (1,1) (D) The curve x=y^3 from (0,0) to (1,1). Homework Equations \int...
  40. J

    Finding the Line Integral of a Tangential Component with Parameterization

    Finding line integrals -- please help! Given F = y/(x^2 + y^2) i - x / (x^2 + y^2) j Find the line integral of the tangential component of F from (-1,0) to (0,1) to (1,1) to (1,0) (assuming F is NOT path independent). --- I tried parameterizing each of the three paths using the formula r(t)...
  41. I

    Why Does the Line Integral of a Square Path's Perimeter Equal Zero?

    When I take the line integral around a square shape path "C" as follows: From A to B to C to D to A C1 = A(0, 0) to B (4, 0) t i 0 <= t <= 4 C2 = B (4, 0) to C (4, 7) 4 i + (t - 4) j 4 <= t <= 11 C3 = C (4, 7) to D (0, 7) (15 - t) i + 7 j 11 <= t <= 15 C4 = D (0, 7)...
  42. V

    Should You Add dy to the Line Integral Expression?

    Homework Statement Hello, I'm writing a summary of all calculus I've learned during this term and now I'm on line integrals. I wrote this so far: http://img17.imageshack.us/img17/9776/algebrac.jpg But I have Sigma of x and y (a similar expression was in my lecture notes), but there is no dy...
  43. B

    Evaluating Line Integrals Along a Curve

    If a question says something like: "evaluate \int(x*z*y)dx - (x-y)dy + (x^3)dz from (1,0,0,) to (1,0,2pi) along the curve (x,y,z)=(cos(t),sin(t),t)" or something like that, this is just basically splitting up a line integral? In my example, it would be the same as: \intcos(t)*t*sin(t)) *...
  44. Saladsamurai

    How do I compute the 3 individual line integrals for a given vector field?

    Line Integrals (yayyy!) Homework Statement Okay, so I have already done it using the surface integral; now I need to compute the 3 individual line integrals. By definition, the integral (I will call it I since I am that creative) is given by: I=\oint v\cdot\, dl v=<xy, 2yz...
  45. H

    Calculate Line Integrals for Vector Field F on C1 and C2

    Homework Statement Calculate \intF dr if C = C1 + C2 where C1 is the line segment from P1(-1,pi,-1) to P2(0,0,0) and C2 is the line segment from P2(0,0,0) to P3(2,0,4) vectorF= yz i + (xz - e^(z)siny) j + (e^(z)cosy + xy) k The Attempt at a Solution Im having problems setting up the...
  46. N

    Calculating Line Integrals: Solving for Limits and Using Parametric Equations

    Evaluate the line integral \int y^(2) dx + xy dy from A(1,0) to B(-1,4) with C: x = 1-t, y = t^(2), 0≤t≤2 I used: Do I make the limits from 0 to 2? What do I do with the A(1,0) and B(-1,4)? Please help? Thanks.
  47. C

    Line Integrals Complex Numbers

    Hi, I am currently studying complex numbers and I am at the part we have to find line integrals over a simple closed curve gamma(t).. I know the definition, but when i read a problem I am n ot sure how to parameratize the curve. I was wondering if there are some tricks to this. Would...
  48. C

    Line Integrals Complex Numbers

    Hi, I am currently studying complex numbers and I am at the part we have to find line integrals over a simple closed curve gamma(t).. I know the definition, but when i read a problem I am n ot sure how to parameratize the curve. I was wondering if there are some tricks to this. Would...
  49. S

    Line Integrals (Complex Variables)

    Homework Statement i) Define a path \gamma whose image is the ellipse \frac{x^2}{a^2} + \frac{y^2}{b^2} = 1 traced counterclockwise. ii) Show that \int \frac{1}{z} dz = \int \frac{1}{z} dz for a suitable circle \beta (NOTE: THE FIRST INTEGRAL IS OVER THE ELLIPSE \gamma, THE SECOND ONE IS...
  50. B

    Integrals for Area and Line Length of Closed Loops with Unknown Shape

    Homework Statement I'm trying to set up a couple integrals. Suppose you have a closed loop and you want to find its area. You don't know what the shape of the loop is. All you know is that the length of the loop is L. The Attempt at a Solution These are my integrals. I just...
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