# Rotating reference frame help

1. May 28, 2014

### natalie

1. The problem statement, all variables and given/known data

I have attached the problem as a picture on this post, am really really unsure on how to start!

so far the only thing i can think of doing is using this equation

$$(\frac{d^{2}r}{dt^{2}})_{s}$$ = $$( \frac{d^{2}r}{dt^{2}})_{s'} + 2ω \times (\frac{dr}{dt})_{s'} + \dot{ω} \times r + ω \times [ω \times r]$$

And now just solve for r, but in the s reference frame ?

any help appreciated really stuck.

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• ###### Screen Shot 2014-05-28 at 12.33.53.png
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2. May 29, 2014

### voko

Not even part (i)?

3. May 30, 2014

### natalie

No, I dont see how it works?

4. May 30, 2014

### voko

Assume that the rod is pointing momentarily north.

What forces acting on the bead, in the inertial frame, can you think of? What are their directions?

5. May 30, 2014

### vanhees71

Hm, I must admit that I always have trouble using forces to derive the equations of motion. If you have Hamilton's principle at hand, it's way simpler to use the Euler-Lagrange equations and then work out the forces at the very end ;-)).

6. May 30, 2014

### voko

That's cheeeeeating! :)

7. May 30, 2014

### natalie

so basically, if i understand correctly, the rod is lying in the x' axis. we have a weight force, and a normal force. thats in the intertial reference frame? the weight force cancels out the normal....

8. May 30, 2014

### vanhees71

9. May 31, 2014

### voko

If the weight cancelled the normal force, the bead would have zero resultant force acting on it. What it is the motion under zero resultant force? Does that seem plausible in the situation at hand?