1. Limited time only! Sign up for a free 30min personal tutor trial with Chegg Tutors
    Dismiss Notice
Dismiss Notice
Join Physics Forums Today!
The friendliest, high quality science and math community on the planet! Everyone who loves science is here!

Expressing a circle in the form r(t) = x(t)i + y(t)i +z(t)k

  1. Jan 7, 2009 #1
    I learnt all the hard (at my level) bits like grad, div, curl and now I'm falling at the first hurdle on the exam papers:

    The question is: Express the circle of radius 3, centred at (1,0,3) and lying in the (x,z) plane in the form of r(t) = x(t)i + y(t)j + z(t)k

    I was hoping there was someone who wouldn't mind taking me through this step by step especially if there is a simple general equation as I have looked everywhere. And also what to do if it is in the other planes etc.

    Thank you,


    P.s. Sorry if this qualifies as homework, I thought that it didn't.
  2. jcsd
  3. Jan 7, 2009 #2


    User Avatar
    Science Advisor

    x(t)=3(cos(t) - 1)
    z(t)=3(sin(t) - 3)

    When the circle is in a plane perpendicular to one of the axes, it is easy as you can see.

    For the general case, it is more complicated. You can set it up in a coordinate system in the given plane and then transform into the global coordinates.
  4. Jan 8, 2009 #3
    :approve: Thanks alot, I don't think i'll be needing anything more complicated than this so greatly appreciated.

Share this great discussion with others via Reddit, Google+, Twitter, or Facebook