Line integral Definition and 404 Threads

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. Y

    Finding work done by object along circular helix: Line Integral

    Homework Statement An object weighing 1.2 pounds travels along a helix given by x=cost, y=sint, z=4t, 0<=t<=8pi. Find the work done by the object. Let's keep this in ft. Homework Equations g=32.174 ft/s2 f=m*g f=w*d The Attempt at a Solution r(t)=cos(t)i+sin(t)j+4(t)k I know I need an F...
  2. M

    What is the Line Integral of a Semicircle with a 45 Degree Angle?

    so I have a semi circle that goes from \frac{5\pi}{4} to \frac{\pi}{4} so the angle between the x-axis the radius of the circle is 45 degrees. I have, letting the radius = a) \frac{1}{a} \int \.dl this is going to have an x and y component, I know the x component is 2a in the...
  3. M

    Kinetic Energy Interpreted as Line Integral?

    Homework Statement From the 1984 Ap Physics C Mechanics Exam: If a particle moves in such a way that its position is described as a function of time by x = t3/2, then its kinetic energy is proportional to: (a) t2 (b) t3/2 (c) t (d) t1/2 (e) t0 (i.e. kinetic energy is constant)...
  4. P

    What is the approach to calculating line integrals in a vector field?

    First I want to greet everyone because I am new here. I have attended to applied electromagnetic course which seems to be pretty hard to understand and issues came up at very first time after I went at calculations. I try to explain this as good as possible. 1. Vectorfield F(x,y,z) =...
  5. S

    Calculating Line Integral of (x^3-y^3)dx +(x^3+y^3)dy

    1.find the line integral of (x^3-y^3)dx +(x^3+y^3)dy over r, where r is the boundary of the region limited by x^2+y^2=1 and x^2+y^2=9 Homework Equations 3. i found that the line integral over the curve x^2+y^2=1 is 3*Pi/2 and the double integral of the region limited by...
  6. M

    Line integral in polar coordinates

    Homework Statement calculate: \oint \frac{2-y}{x^2+(y-2)^2} dx + \frac{x}{x^2+(y-2)^2} dy where y = \sin{t} + 2, x = \cos{t}, 0 \leq t \leq \pi Homework Equations Green's Theorem. The Attempt at a Solution In what order should I do everything? I need to find the derivaties...
  7. M

    Line Integral in Cylindrical Coordinates

    Homework Statement Find the value of the (surface) integral \int curl \textbf{A} \bullet \textbf{a} if the vector \textbf{A}=y \textbf{i}+z \textbf{j}+x \textbf{k} and S is the surface defined by the paraboloid z=1-x^2-y^2 Homework Equations x=s\cos\phi y=s\sin\phi...
  8. M

    Line Integral: A from (1,0,0) to (3,0,0) on Semi-Circular Path

    Homework Statement Calculate the line integral of A between to points x=1 and x=3 along the semicircular path with a center at x=2 Homework Equations A=kx in the x hat direction. \int A \bullet dl dl = ds s hat +s d\phi \phi hat +dz z hat The Attempt at a Solution My...
  9. H

    How Do You Calculate a Line Integral for a Helical Path?

    Homework Statement \inty dx +x dy + z dz c= helix x = 3 cos t y = 3 sin t z = 4t 0\leqt\leq2\Pi Homework Equations \int F(x,y,z) ds ds=\sqrt{[Fx(x,y,z)]+[Fy(x,y,z)]+[Fz(x,y,z)]}dt (still learning latex the partial derivatives are suposed to be...
  10. K

    What is the line integral of grad(f) around the unit circle in the xy plane?

    EDIT: SORRY, I didn't read the directions. It says, "Answer the following short questions: If true, justify, if false give a counterex- ample." I'm certain that this question is one of the "false" ones, which is why I was so confused. LOL Homework Statement Let f(x, y, z) = y - x. Then the...
  11. A

    Is this correct. Evaluate the line integral

    Evaluate the line integral \int F \circ dr for (a) F(x,y) = (x - y) * i + xy * j and C is the top half of a circle of radius 2. Here's green's theorem. Double integral ( dQ/ dx - dP/dy) dA dQ/dx = y dP /dy = -1 It becomes ∫∫ (y +1) dA y = r sin Θ so...
  12. C

    Understanding Line Integrals: Scalar vs Vector Fields

    Well i know that the line integral is given a scalar function f. equation1 But the line integral is also given a vector field F. equation2 So, given scalar function f and taking the gradient vector of it in order to turn it into a vector field F. Why is equation1 not equal to equation2?
  13. B

    Finding limits of line integral

    Homework Statement Integrate along the line segment from (0,0) to (\pi,-1) The integral \int_{(0,1)}^{(\pi,-1)} [y sin(x) dx - (cos(x))]dy Homework Equations The Attempt at a Solution I have used the parameterization of x=\pi t and y= 1-2t To get the integral...
  14. C

    Calculating Work Along a Path with a Force Proportional to Distance Cubed

    Homework Statement A particle is attracted towards the origin by a force proportional to the cube of its distance from the origin. How much work is done in moving the particle from the origin to the point (2,4) along the path y = x^2 assuming a coefficient of friction \mu between the particle...
  15. B

    Evaluating Line Integral F over C: a Step-by-Step Guide

    Homework Statement Let F=(3x+2y)i+(2x-y)j Evaluate \int_{C}F . dr where C is the line segment from (0,0) to (1,1) Homework Equations \int_{a}^{b}[f(x(t),y(t))x'(t) + g(x(t),y(t))y'(t)]dt The Attempt at a Solution How do I choose the correct values of x and y as a function...
  16. K

    How can we visualize line integrals in layman's terms?

    Hello Everyone I have a few questions regarding line integrals. First what are they? What is the difference between them and the normal integrals? For eg, The normal integrals can be easily understood by visualizing the area bounded by them, in the same way is there any way as to visualize the...
  17. T

    Line Integral over Vector Field?

    Not exactly a homework problem, a problem from a sample test. I'm boning up for my qualifying exam. Homework Statement Consider the vector field: F = (ax + by)i + (cx + dy)j where a, b, c, d are constants. Let C be the circle of radius r centered at the origin and going around...
  18. J

    Calculate Line Integral for a Function on a Level Surface | Homework Equations

    Homework Statement Let f(x,y,z) be a function of three variables. Suppose that C is an oriented curve lying on the level surface f(x,y,z) = 5. Find the integral grad f dot dr. Homework Equations The Attempt at a Solution integral grad f dot dr = integral f(q) - f(p) not...
  19. J

    Solving a Line Integral: Finding the Value of \int -2y dx + x^2 dy

    Hello all, I am trying to solve a line integral: Find the value of \int -2y dx + x^2 dy over the circle x^2 + y^2 = 9 as you can see, this is a line integral, and I am trying to figure a quick way how it should be solved. I thought of converting coordinates to (sint,cost) which will...
  20. B

    Question: Calculating Work with a Line Integral

    Homework Statement Find the work doneby the force field F on a particle that moves along the curve C. F(x,y)=xy i + x^2j C: x=y^2 from (0,0) to (1,1) Homework Equations \intF dot dr=\int^{b}_{a}F(r(t))dotr'(t)dt The Attempt at a Solution Okay, so I parametrized x=t and y=t^2...
  21. X

    Triangle Line Integral: Evaluating f(x,y)=(x+2y) Along Triangle C

    Let C be the triangle in the plane from (0,0) to (1,1) to (0,1) back to (0,0). evaluate the line integral of f along C if f(x,y)=(x+2y). attempt: C1: x=t y=t ds=root(1)dt, integrated t+2t from 0 to 1 to get 3/2 C2: x=-t ds=root(1)dt, integrated -t from -1 to 0 to get 1/2 C3: y=-t...
  22. X

    How Do You Properly Set Bounds for a Line Integral?

    Let C be the line segment from (0,0,0) to the point (1,3,-2). evualuate the line integral of f along C if f(x,y) = (x + y^2 -2z) so far i was able to write the parametric form x = t y=3t and z=-2t the square root of all the derivatives is root(14). so i get root(14) times integral of...
  23. M

    Calculating Line Integral of Lamda Curve

    Homework Statement A curve lamda starts in (0,0) and fallows a straight line from x = 0, y = 0 to x = 1, y = 0 and then another straight line to x = 2 and y = 1. Calculate the line integral I = S vdr where S is an integral s v = (x+3y)i + (3+y)j Homework Equations...
  24. E

    Line Integral Homework: Solving for the Result Along the x-Axis

    Homework Statement http://img7.imageshack.us/img7/1764/capkgc.th.jpg Homework Equations The Attempt at a Solution Okay I already got the result for the line integral along the circle, but I am confused how to get the line integral in the x-axis? To get the final result I just...
  25. N

    Line Integral (where the path is not single valued)

    I'm a bit confused as to how to solve this line integral: Evaluate I = The integral of (x+y)dx from A (0,1) to B (0,-1) along the semi-circle x^2 + y^2 = 1 for for x is equal to or greater than 0. So far have have got: if x^2 + y^2 = 1 then y= + SQRT of (1 - x^2) which I believe...
  26. W

    Line Integral dl in spherical polar coordinates

    Homework Statement Hi guys, I'm trying to evaluate a line integral, Integration of Vector A dot dL The vector A was given to be a function of r, theta and fi in spherical polar coordinates. The question states that an arbitrary closed loop C is the circle parametrised by fi at some...
  27. S

    Line integral, problems with substitution (probably)

    Homework Statement I am trying to solve a line integral (bear with me, I am new to calculus!) and my basic skills of integration seem to fail me. I am sure the mistake is quite obvious, as I keep getting the wrong answer, 2, when it should be ~2.69 Homework Equations \int_C 4x^3dS C is the...
  28. W

    Can someone define a line integral?

    I have just begun exploring the topic of line integrals for my Calculus 3 class. Although I can perform the calculation properly, I don't understand the physical significance of what I've just calculated. For example, I know that when I calculate the integral of a function which is defined...
  29. W

    Evaluating a Line integral in spherical polar coordinates

    Homework Statement Consider the vector potential A = cr * [(sin theta)^2 * (cos fi) * (sin fi) + (cos theta)^2 ) er + (sin theta) cos (theta) * [(sin fi) (cos fi)  − 1] e theta + {(sin theta) (cosfi)^2 } efi er: in the er direction e theta: in the e theta direction...
  30. G

    Simple line integral problem I cant seem to get

    I have to evaluate the line integral : \oint_{}^{} (2x + y)dx + xydy between (-1,2) and (2,5) on the curve: y = x + 3 So, what I did was: \int_{-1}^{2} (3x+3)dx + \int_{2}^{5} (x^{2} + 3x)dx However, this is wrong and I am not sure why! Can someone please guide me? Thanks alot!
  31. G

    Evaluation of a (parabolic) line integral with respect to arc length

    Homework Statement Evaluate the line integral \[ \int_c yz\,ds.\] where C is a parabola with z=y^2 , x=1 for 0<=y<=2Homework Equations A hint was given by the teacher to substitute p=t^2 , dp=(2t)dt and use integration by parts. I also know from other line integrals with respect to arc length...
  32. K

    Line integral ad electric charge

    Homework Statement The force exerted by an electric charge at the origin on a charged particle at point (x,y,z) with position vector r = <x,y,z> is F(r) = Kr / |r|^3 where K is a constant. Find the work done as the particle moves along a straight line from (2,0,0) to (2,1,5). Homework...
  33. B

    What is the work done in moving a particle around a closed curve?

    Homework Statement For the field \bold{F} = (y+z) \bold{i} - (x+z) \bold{j} + (x+y) \bold{k} find the work done in moving a particle around the following closed curve: from the origin to (0,0,2π) on the curve x=1-cos t, y=sin t, z=t; and back to the origin along the z-axis. The answer is 2π...
  34. D

    Line Integral + Potential Difference Problem Need

    Homework Statement The cyclotron is a device for accelerating charged particles. It requires changing electric fields and a magnetic field, but it can be modeled using (non-physical) static electric fields and potentials as we will do in this problem. Keep in mind that these fields cannot...
  35. L

    Find Value of Line Integral Homework - E.dl, P Circular Path Centered on Origin

    Homework Statement There is a constant electric field E = E0sin(kz+wt+pi/3) k(direction vector). What is the value of the line integral(P) B.dl, where P is a circular path, centered on the origin, lying in the xy-plane, having radius r? Homework Equations integral E.dl = -dI/dt The...
  36. S

    How can I derive a three-variable function from two given points?

    Recently I was working through a problem involving a force field, and came up with a question I could not answer, so I thought I would post it here. I solved the problem using a vector representation and a line integral, and although I am sure the answer is correct, I would like to solve it by a...
  37. D

    What Is the Value of the Line Integral Over a Curve on a Level Surface?

    Greetings, I'm having trouble deciding what to do, and in what order for this question: Suppose F = F( x, y, z ) is a gradient field with F = \nablaf, S is a level surface of f, and C is a curve on S. What is the value of the line integral (over C) of F.dr ? I think I'm a little confused...
  38. S

    Line Integral of F(x,y,z) over Unit Circle

    Homework Statement What is the line integral of F(x,y,z) = (xy, x, xyz) over the unit circle c(t) = (cost, sint) t E (0,2pi) ? Homework Equations integral= (f(c(t))*c'(t))dt) The Attempt at a Solution Ok, so I tried solving this like I would any other line integral using the given...
  39. S

    Integrating Line Integrals over Ellipses

    Homework Statement Calculate the anti-derivative of ydx where c in the ellipse 4x^2 + 25y^2 = 100 Homework Equations Definition of a line integral The Attempt at a Solution I tried parameterizing the equations but I sure if am making the right choice
  40. J

    Line integral of a vector field.

    Hi all, I'm new to the forums so if i do something stupid don't hesitate to tell me. Anyway I'm struggling with this problem: I could do part a ok, but part b has me stumped, I am in the second year of a physics degree and this is a from a maths problem sheet, i haven't done line...
  41. N

    Line integral - finding the arc length

    a curve is given as 3 parameters of t: x=a(3t - t^3), y=3a(t^2), z=a(3t + t^3) i have to find the arc length measured from origin and curvature as functions of t. would i be correct in using the integral at the bottom of page 2 here: http://homepages.ius.edu/wclang/m311/fall2005/notes17.2.pdf
  42. Saladsamurai

    Evaluating a Line Integral: Exploring the Questions

    Homework Statement Evaluate the line integral, where C is the given curve: \int_C\,y\,ds \, \,\,\,\,C:\,x=t^2\,\,\,\,y=t for t between 0 and 2 (out of curiousity, how do you make the "greater than or equal 2" in LateX) Okay, in the book the line integral is defined as \int_C F\cdot...
  43. A

    Problems with conversions to spherical coordinates involving a line integral

    Homework Statement given the vector A = 4r + 3theta -2phi , find its line integral around the closed path. (the figure contained in the book is a straight line along the x-axis extending to radius a, with a curved portion of a circle with radius a centered at the origin curving back to the...
  44. CalleighMay

    Find the value of the line integral ?

    Hey guys! I have been on the forum for about a week or so and have compiled a lot of information and techniques to help me understand calculus, so i really appreciate everyone's help! I am a soon-to-be freshman in college and am taking a summer class, calculus II (took calc I in HS). This is...
  45. C

    What is the definition of a line integral?

    How would you DEFINE the line integral: int_aroundc[P(x,y)dx + Q(x,y)dy]
  46. F

    How can you use the line integral to find the work done by a conservative force?

    Homework Statement A 160-lb man carries a 25-lb can of paint up a helical staircase that encircles a silo witha radius of 20 ft. If the silo is 90 ft high and the man makes exactly three complete revolutions, how much work is done by the man against gravity in climbing to the top...
  47. F

    How to Correctly Calculate the Line Integral Over a Semicircular Path?

    Homework Statement Evaluate the line integral, where C is the given curve. integral of xy^4. C is the right half of the circle x^2 + y^2 =16 Homework Equations integral of line integral= integral of r(t) |r'(t)| dtThe Attempt at a Solution I set up a parametric equation to be r(t)=(4cost...
  48. D

    Stokes theorem equivalent for cross product line integral

    "Stokes theorem" equivalent for cross product line integral Homework Statement I am aware that the vector path integral of a closed curve under certain conditions is equivalent to the flux of of the curl of the vector field through any surface bound by the closed path. In other words, Stokes...
  49. A

    How to Attempt a Path Integral Problem with Green's Theorem?

    Homework Statement A region R is bounded by the curves y = 12.x and y=5.x^2 If I = (5/12).x^2 .y i + (y/12.x) j find the contribution to the line integral Integral I.dl = Integral (I(x) dx + I(y) dy) taken in the anti clockwise direction with respect to the region R along the curve...
  50. D

    Line integral over plane curve

    Homework Statement Integrate f(x,y) = (x^3)/y over the curve C: y = (x^2)/2, 0 <= x <= 2 Homework Equations The Attempt at a Solution So far I'm only familiar with line integrals over space curves such as questions like this: Find the line integral of f(x,y,z) = x + y + z over the...
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