## TomLikesPhysics 2 years ago r(t)=(2t, wt, 4t) in cylindric coordinates. How do I find v(t)?

1. TuringTest

w is omega?

2. TomLikesPhysics

Yes

3. TuringTest

I can't see how it is anything other than just differentiating wrt t

4. TomLikesPhysics

I think the problem is that the unit vectors in cylindric coordinates also vary with time so it is not just v(t)=(2,w,4)

5. TuringTest

so the directions here are$\hat r,\hat\theta,\hat z$I suppose, eh?

6. TomLikesPhysics

right

7. TuringTest

8. TomLikesPhysics

No, however I just computed v(t)=(2, 2t*w, 4) but I don´t know if is correct or not.

9. TomLikesPhysics

I also have no clue how I could ask wolfram alpha to check that.

10. TomLikesPhysics

I used this formula but I am not entirely sure if this formula fits that problem.

11. TuringTest

I have never seen that formula, so I can't verify it...

12. TomLikesPhysics

I thought this is a "simple" problem.^^

13. TuringTest

http://www.maths.ox.ac.uk/system/files/coursematerial/2012/1115/77/CylCoords.pdf that formula you have seems to be right, though I can't seem to see where they get the extra rho from

14. TomLikesPhysics

The extra rho comes from the derevative of the unit vector e in the direction of phi.

15. TuringTest

ahh, okay, I had to read that sheet a but closer to get it thanks!

16. TomLikesPhysics

No problem, you´re welcome.