# What is a function that describes motion in a circular path?

1. Feb 24, 2012

### LearninDaMath

If an object is moving in a perfect circlular path, what function(s) describe its path as a function of time?

2. Feb 25, 2012

### vivekrai

It could be $\vec{r}\cdot\vec{v} = 0$ or even $x^2+y^2=r^2$.

r = Position vector, v = Velocity vector.

3. Feb 25, 2012

### Redbelly98

Staff Emeritus
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.

4. Feb 28, 2012

### LearninDaMath

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,
LearninDaMath

Last edited: Feb 28, 2012
5. Feb 28, 2012

### SammyS

Staff Emeritus
The functions usually used are sine and cosine.

(Not giving too much away!)

6. Feb 28, 2012

### LearninDaMath

7. Feb 28, 2012

### Redbelly98

Staff Emeritus

8. Feb 28, 2012

### LearninDaMath

9. Feb 28, 2012

### Staff: Mentor

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

and you know x = r.cosθ
etc.