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Homework Help: What is a function that describes motion in a circular path?

  1. Feb 24, 2012 #1
    If an object is moving in a perfect circlular path, what function(s) describe its path as a function of time?
  2. jcsd
  3. Feb 25, 2012 #2
    It could be [itex]\vec{r}\cdot\vec{v} = 0[/itex] or even [itex]x^2+y^2=r^2[/itex].

    r = Position vector, v = Velocity vector.
  4. Feb 25, 2012 #3


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    None of your expressions contain time as a variable, as requested in the OP. That being said, we shouldn't give things away without LearninDaMath showing some attempt towards answering the question.
  5. Feb 28, 2012 #4

    Please see thread https://www.physicsforums.com/showthread.php?t=580771 Post #8-16 for thorough attempt and on-going progress on this topic. Rest assured no information is being given away without effort on my part. I appreciate the expertise of physicsforums members who take some time to help out those of us who are learning the basics of various subjects and, within this or any of the threads I have created, it would be inaccurate for anyone to accuse anyone of trying to simply recieve or provide answers without a fair reciprication of effort.

    This is my first time logging into and visiting physicsforums since Feb 25. I have had a very tough work schedule this weekend. But I am not finished exploring the topic of this thread. It is not a specific hw problem. Nor am I seeking an answer to a specific hw problem. This section of physicsforums is for hw problems, hw related problems, or anything related to textbook style questions.

    Thank you for your concern, but there is nothing to worry about here. If you feel it's absolutely necessary, you could combine this thread into the thread I cited above (although that would make the other thread more confusing to read through.) Or, just remove the warning on this thread since this question is not a specific hw question. Or leave the warning as is so it can serve as a reminder that I should thoroughly preface each thread with whether or not it is a hw problem or not. Perhaps I should have referenced the above thread when making this thread to avoid this confusion. As soon as I can get back to this physics topic, I will continue it. Right now, I have to concentrate on Calculus. Sorry for any confusion.

    Thanks, respectfully,
    Last edited: Feb 28, 2012
  6. Feb 28, 2012 #5


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    The functions usually used are sine and cosine.

    (Not giving too much away!)
  7. Feb 28, 2012 #6
  8. Feb 28, 2012 #7


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    FYI, LearninDaMath has actually made considerable headway on this question:
  9. Feb 28, 2012 #8
    Redbelly, thanks. At the time of making this thread, I had made so much progress with gneill in the prior thread, that our discussion was starting to move beyond the content of the original post of that thread. Didn't know if the progress was supposed to continue in the same thread or if a new thread should be made so as to stay on par with the title of the thread so that anyone else searching for the same questions in the future would find the info easier. However, i'm content with the flow of information in the other thread and there seems to have been no direct need (for me) to create a new thread other the search engine convenience for others that i've just described. I will be more descriptive in my original posts in the future.
  10. Feb 28, 2012 #9


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    If it's rotating at a steady rate, then θ ∝ t
    ⇔ θ = k.t

    and you know x = r.cosθ
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