What is Polar coordinates: Definition and 586 Discussions

In mathematics, the polar coordinate system is a two-dimensional coordinate system in which each point on a plane is determined by a distance from a reference point and an angle from a reference direction. The reference point (analogous to the origin of a Cartesian coordinate system) is called the pole, and the ray from the pole in the reference direction is the polar axis. The distance from the pole is called the radial coordinate, radial distance or simply radius, and the angle is called the angular coordinate, polar angle, or azimuth. The radial coordinate is often denoted by r or ρ, and the angular coordinate by φ, θ, or t. Angles in polar notation are generally expressed in either degrees or radians (2π rad being equal to 360°).
Grégoire de Saint-Vincent and Bonaventura Cavalieri independently introduced the concepts in the mid-17th century, though the actual term polar coordinates has been attributed to Gregorio Fontana in the 18th century. The initial motivation for the introduction of the polar system was the study of circular and orbital motion.
Polar coordinates are most appropriate in any context where the phenomenon being considered is inherently tied to direction and length from a center point in a plane, such as spirals. Planar physical systems with bodies moving around a central point, or phenomena originating from a central point, are often simpler and more intuitive to model using polar coordinates.
The polar coordinate system is extended to three dimensions in two ways: the cylindrical and spherical coordinate systems.

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  1. O

    Polar coordinates (trig question)

    Homework Statement Given r = 2tan(theta)sec(theta) Find cos(theta) then use inverse key to find sec(theta) The answer given in the solution guide is y = 1/2 x^2 Attempt at solution Since tan = sin/cos and sec = 1/cos We have r = 2sin/cos * 1/cos So rcos^2 = 2sin rcos^2 is defined...
  2. Y

    Polar coordinates and integral

    Homework Statement I have a problem I hope you guys can help me with. It's quite simple I think, but there is one thing that I can't figure out. Homework Equations I have to use polar coordinates to evaluate this integral: See image The Attempt at a Solution I really don't have...
  3. S

    Volume Using Polar Coordinates

    Homework Statement Use polar coordinates to find the volume bounded by the paraboloids z=3x2+3y2 and z=4-x2-y2Homework Equations The Attempt at a Solution Somehow, through random guessing, I managed to get the right answer, it's just that I don't understand how I got it. Also, because the z is...
  4. S

    Integral of f over the surface of a sphere (in spherical polar coordinates)

    I have a function f(r, \phi, \vartheta) = 3cos\vartheta. Evaluating the repeated integral of this function over the surface of a sphere, centered at the origin, with radius 5, I have come up with 0 as my result. I'm not sure if this is correct. I've double checked my calculations, and tried...
  5. J

    Calculating Arc Length in Polar Coordinates

    Homework Statement Find The length of r=sin³(x/3) 0<x<3pi/2 2. The attempt at a solution well first i found r'=3.cos(x/3).1/3.sin²(x/3)=cos(x/3)sin²(x/3) r²=cos²(x/3)sin^4(x/3) then i put the formula integral of radical (r'²+r²)dx and I'm stuck here any help?
  6. A

    Is this ok with Polar coordinates?

    Homework Statement we have this diagram were it says that the change in the unit vector der equals in magnitude the change in the angle betwen the two unit vectors er. Could someone explain me why is this? I include the diagram named Polar coordinates.
  7. B

    What is the vector field expressed in spherical coordinates?

    Express the following vector field in spherical coordinates. (The answer should be in a form that uses the unit vectors of the curvilinear coordi- nate system and coefficient functions that are written in terms of the curvilinear coordinates.) \underline{F} = -y \underline{i} + x...
  8. C

    Analytic mechanics in polar coordinates

    Homework Statement A mass follows the path of a cardioid r=1+sinφ with given speed, what is its period? Homework Equations The Attempt at a Solution I attempt to do an integral on polar coordinates to find the distance covered by the mass first. The integral I derived is \int_0^{2\pi}...
  9. P

    Polar coordinates in mecanics?

    Ok, here is my problem. I haven't taken anything vector related since at least one year ago. And back then, I wasn't such a good student.. So now my past has come back to haunt me.. I still have some basic notions, but other than that, I pretty much forgot things...
  10. dav2008

    Laplace Operator in Polar Coordinates

    Homework Statement Compute \nabla \cdot \nabla f in polar coordinates.Homework Equations The Attempt at a Solution It seems like a straightforward dot product yields \nabla \cdot \nabla f = {\partial^2 f \over \partial \rho^2} + {1 \over \rho^2} {\partial^2 f \over \partial \theta^2} +...
  11. T

    The Laplace Equation in Polar Coordinates

    Homework Statement \frac{\partial^2f}{\partial x^2}+\frac{\partial ^2f}{\partial y^2}= 0 Homework Equations Show that the equation above is equal to: \frac{\partial^2f}{\partial r^2}+\frac{1}{r^2} \frac{\partial ^2f}{\partial \theta^2} + \frac{1}{ r} \frac{\partial f}{\partial r}= 0...
  12. N

    Divergence in Polar Coordinates

    Why is \nabla\cdot\vec{A}=\frac{1}{r}\frac{\partial}{\partial r}(rA_{r})+\frac{1}{r}\frac{\partial}{\partial \theta}(A_{\theta}) Where \vec{A}=A_{r}\hat{r}+A_{\theta}\hat{\theta} And \nabla=\hat{r}\frac{\partial}{\partial r}+\hat{\theta}\frac{1}{r}\frac{\partial}{\partial \theta} Instead of...
  13. A

    What is the Limit of polar coordinates?

    Homework Statement I need to evaluate this limit by converting to polar coordinates: lim (x,y) -> (0,0) of (x^2 + xy + y^2) / x^2 + y^2 Homework Equationsx = rcos(theta), y = rsin(theta) The Attempt at a SolutionSo switching to polar I get: [(rcos(theta))^2 +...
  14. S

    What are the Polar Coordinates for this Problem in Homework Statement?

    Homework Statement http://img127.imageshack.us/img127/2695/coord2pq5gm6.jpg Homework Equations \underline v = \dot r\;\underline e _r + r\dot \theta \;\underline e _\theta \underline a = \left( {\ddot r - r\dot \theta ^2 } \right)\underline e _r + \left( {r\ddot \theta + 2\dot r\dot...
  15. D

    Change of variables to polar coordinates

    I thought I grasped coordinate changes well, but now I've run into some problems. Usually I would have some function f(x,y) and transformation equations like s = a*x+b*y . I would apply chain rule and stayed left with new equations in new variables. (old ones get away through...
  16. K

    Polar Coordinates and finding points

    This is an example problem that I can't understand how the answer came out to be this way: Q: Sketch the polar curve \Theta = 1. A: A picture of a line that goes diagonal with points that go (1, 1) (2, 1) (3, 1) etc. I do understand that if the angle is 1, then the line is such that it's 1...
  17. C

    Convert into polar coordinates

    Homework Statement I'm trying to solve a double integral of a function which is bounded by the ellipse: \frac{(x-2)^2}{16}} + \frac{(y-4)^2}{36}} = 1 And I can't figure out how to write this in polar coordinate form, and also what my bounds for theta and radius would be. Homework Equations I...
  18. G

    Area of a graph with polar coordinates

    I'm trying to plot the graph r = sin 3t and find its area. This is how far I've gotten: The graph looks like a plane propellor with one propellor pointing downward, and two pointing up-left / up-right, with the length of each equal to 1. Now to get the area... I have to figure out where...
  19. D

    Transform to polar coordinates

    Could someone please convert this double integral to polar coordinates? 0<x<1, x*2<y<1 Int.Int f(x,y)dxdy
  20. A

    Double Surface Integrals in Polar Coordinates

    Homework Statement Find the surface area of the cone z=3x^2+y^2and above a region in the xy-plane with area 4. Homework Equations double integral sqrt( (dz/dx)^2 + (dz/dy)^2 +1) The Attempt at a Solution I was able to simplify the equation, I just don't know what to do...
  21. J

    Deriving Velocity in Polar Coordinates

    Hi, I've just gone through a derivation and would like some confirmation that my reasoning is correct: Say the position of a particle is expressed in polar coordinates as (\phi,r) If we want to describe it's velocity v we need to differentiate both components(angular and radial) with...
  22. T

    Double integration using polar coordinates

    Ok, got a few small problems. Just gaps in my knowledge I suppose, wonder if anyone can help. A bit stuck on how to work out the limits for theta. Everything else is fine, it's just that. I know if it says in the first quadrant that it's pi/2 and 0 but that's a really basic one, everything...
  23. T

    Understanding Area in polar coordinates

    One of the problems I am working on is confusing me. Given r=2cos(theta) and r=2sin(theta), you get a graph with two circles intersecting each other at pi/4. So I worked it out, using the Area of a Polar Region formula. \int\frac{1}{2}\pi*r^{2}. When I got an answer, I checked and...
  24. T

    Polar coordinates finding area between two curves

    Homework Statement Homework Equations r=sinx r= cosx Ok , i need help how to properly select the integral to evaluate the area they make. Can someone please show me how , i know how to evaluate it just having hard times with integrals The Attempt at a Solution
  25. T

    Polar Coordinates and Conics, bad

    Were on the conic section. I need help how to choose the right interval to evaluate the arc lengh. x=5cost-cos5t and y=5sint-sin5t . I don't get how to choose the inverval to evaluate this, can someone pleasse tell me how. I just don't grasp this.
  26. I

    Evaluating Improper Integrals Using Polar Coordinates

    Homework Statement A.Using polar coordinates, evaluate the improper integral of e^(-10(x^2+y^2))dxdy B. use part A to integrate from negative infinity to positive infinity of e^(-10x^2)dx 2. Homework Equations [/b] The Attempt at a Solution i got part A to be pi/10, but for...
  27. S

    From polar coordinates to heliocentric ecliptic coordinates

    So I've calculated the polar coordinates of a planet, with the sun at the origin and the x-axis being the striped line going from the sun towards point P. Now I have to convert these polar coordinates to heliocentric ecliptic coordinates. To do this, I have to convert to cartesian...
  28. C

    Solution to diffusion equation in 1d spherical polar coordinates

    Ok, I have been given the steady state diffusion equation in 1d spherical polar coordinates as; D.1/(r^2).'partial'd/dr(r^2.'partial'dc/dr)=0 I know that the solution comes in the form c(r) = A+B/r where A and B are some constants. I just don't know how to get from here to there. I...
  29. N

    Cartesian and polar coordinates - integrals

    Homework Statement When dealing with an integral integrated with respect to dxdy, I can convert this to polar coordinates, and then integrate with respect to dr d\theta. But I have to multiply with a "r" before integrating. If I am dealing with an integral with respect to dydz, I can...
  30. N

    Concerning the Gaussion integral in polar coordinates

    I'm looking at the proof for the Gaussion integral in polar coordinates and I don´t understand why theta reaches from 0 to 2pi in the integral since you can´t get a negative value out of an exponential function (and therefor the exponential function is never in the 3rd and fourth quadrant, which...
  31. D

    Parallel transport in flat polar coordinates

    If we have as a manifold euclidian R^2 but expressed in polar coordinates... Do any circle centered at the origin constitute a geodesic? Because I think it parallel transport its own tangent vector.
  32. J

    Polar Coordinates Homework: Converting to Cartesian and Strain Rate Tensor

    Homework Statement The velocity field for a line source in polar coordinates (r,theta) is given by: V=m/(2(pi)r) (in the "e" little r vector direction) convert to cartesian and calculate the strain rate tensor. Homework Equations R=Sqrt(x2+y2); Theta=ArcTan(Y/X); Cartesian...
  33. C

    Polar Coordinates: Solving for Angle in Second Quadrant | 59.1 Degrees

    Homework Statement The angle is 59.1, which is in the second quadrant. Give the angle from the positive x-axis. Homework Equations The Attempt at a Solution 180-59.1=120.9 Does that look right? Thank you very much
  34. G

    Conic sections in polar coordinates

    [SOLVED] conic sections in polar coordinates Homework Statement write a polar equation of a conic with the focus at the origin and the given data. i know it's an ellipse with eccentricity 0.8 and vertex (1, pie/2) The Attempt at a Solution my question is: how do I find the...
  35. J

    Polar Coordinates Angular velocity

    Homework Statement A cameraman standing at A is following the movement of a race car traveling at a speed of 30 m/s. Determine the angular rate (theta dot) at which the man must turn to keep the camera directed on the car at theta = 30 degrees...
  36. G

    Solve Polar Coordinates: y=x^2

    Homework Statement change the following equation into polar form: y=x^2 The Attempt at a Solution r*sin(t) = r^2 * cos(t)^2 stuck after this... my friend suggested that I cancel an r, but won't that get rid of one of the solutions? I'm not really sure how to proceed
  37. P

    Evaluating a Double Integral Using Polar Coordinates

    Okay I have no idea where to start on this example problem: Use polar coordinates to evaulate the double integral e^((x^2)+(y^2))dydx [frist (inner) integal lower limit y= -sqrt(4-x^2) upper limit y=0)] [second (outer) lower limit x=0 upper limit x=2] When I start doing the integral...
  38. H

    Double integration and polar coordinates

    [SOLVED] Double integration and polar coordinates Homework Statement Find the area inside both circles r = 1, and r = 2 sin \theta by double integration in polar coordinates. Homework Equations None The Attempt at a Solution The way the problem is worded sounds a bit...
  39. I

    Polar coordinates and mechanics question.

    Alright, the problem here is that I seem unable to grasp an example given in class. I am not sure if this is due to not copying it down correctly, or if there's something I am just missing. Either way, I know I am not the only one who has had a bit of trouble with this. I'm hoping that someone...
  40. W

    How Do You Calculate the Area Bounded by a Polar Curve?

    [SOLVED] Area of Polar Coordinates Homework Statement Find the area of the region bounded by r=6-4sin\Theta Homework Equations A=(1/2)\int r^{2} d\Theta The Attempt at a Solution I'm not sure what the bounds are but I thought they were 0 to 2pi. Am I wrong if so how then do you go...
  41. C

    How Do You Calculate the Area Bounded by \( r = 8\cos(10\Theta) \)?

    Homework Statement Find the area of the region bounded by r=8cos10\Theta Homework Equations The Attempt at a Solution I set r=0 to find \Theta, which i used for my bounds \Theta=pi/20, 3pi/20 A= \int(1/2)64cos^2(10\Theta) d\Theta
  42. I

    Convert the integral into polar coordinates

    Homework Statement Convert the following integrals into polar coordinates and then calculate them. a) int(0 , 2^(1/2)) int(y, [(4-y^2)^1/2]) xydxdy . Homework Equations x = rcostheta y = rsintheta r = (x^2 + y^2)^(1/2) The Attempt at a Solution Would it simply be: int(0...
  43. B

    Understanding Polar Coordinates and Arc Length Equations

    Homework Statement My book says if you write a plane curve in polar coordinates by p = p(?), a<=?<=b then the arc length is ??(p^2+(p')^2)d? (the integral is from a to b). It doesn't tell me how they got this equation though and I can't figure it out myself. what does the equation p(?) mean...
  44. G

    Coveting ODE to polar coordinates

    Hi, I was wondering how to go about converting a homogeneous ODE of the form M(x,y)dx+N(x,y)dy=0 (where, by definition of a homogeneous ODE, M(tx,ty)=(t^a)M(x,y) and N(tx,ty)=(t^a)N(x,y) ) to polar coordinates. I wan to do this because using substitution of y/x=u and dy/dx=u+xdu/dx to make the...
  45. K

    What are the Polar Coordinates and Speed of a Car on a Straight Road?

    Homework Statement A car P travles along a straight road with a constant speed v = 65mi/hr. At the instant when the angle theta = 60 degrees, determine the values of r (with dot above) in ft/sec and theta (with dot above) in deg/sec. (r = 100ft) The picture has a car on highway and radius...
  46. C

    Laplaces equation in polar coordinates

    The function u(r,\theta) satisfies Laplace's equation in the wedge 0 \leq r \leq a, 0 \leq \theta \leq \beta with boundary conditions u(r,0) = u(r,\beta) =0, u_r(a,\theta)=h(\theta) . Show that u(r,\theta) = \sum_{n=0}^\infty A_nr^{n\pi/\beta}sin(\frac{n\pi\theta}{\beta})...
  47. R

    Finding area in polar coordinates

    Homework Statement "Find the area of the region described: The region that is enclosed by the rose r=4cos3[theta]" Homework Equations A= [integral] (1/2)r^2 d[theta] The Attempt at a Solution I'll use Q as [theta].. I'm not really sure, but I set up (1/2) [integral] (16(cos^2)3Q) dQ ...
  48. R

    Dynamics - velocity from polar coordinates

    Car B is driving straight toward the point O at a constant speed v. An observer, located at A, tracts the car with a radar gun. What is the speed |r(dot)B/A| that the observer at A records? --I've attached a crude version of the example picture. By the way, the angle of the line from the origin...
  49. K

    Intersections of two graphs (polar coordinates)

    Homework Statement Find all points of intersection of the two graphs r=sin \theta and r=cos 2 \theta The Attempt at a Solution sin \theta = cos 2 \theta I use the trigonometric identity cos 2x = (cosx)^2 - (sinx)^2 but it doesn't take me any further.
  50. S

    Newtonian tidal acceleration tensor in polar coordinates

    I'd like to understand how to calculate the components of Newtonian tidal accelaration tensor in polar coordinates. Is any available Internet source which clearly explains the technique with details? Reading James B. Hartle "Gravity" textbook I stumbled on the following Example from...
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