# Special relativity - observing spinning objects

1. Oct 2, 2007

### Mentz114

I did a thought experiment - suppose we have a simple clock comprising a disc rotating with constant angular velocity. We can read off time inervals by counting the revs.

Another observer, passing at constant velocity will see the disc rotating at a slower rate, since moving clocks run slower.

Does this mean that all spinning objects appear to be spinning slower from another frame ?

In other words, does angular velocity transform like time in SR ?

Last edited: Oct 2, 2007
2. Oct 2, 2007

### meopemuk

Yes, I think your observation is correct.

Eugene.

3. Oct 2, 2007

### Mentz114

Hi Eugene,
yes, it seems inevitable. It is a bit puzzling because angular velocity has dimension of reciprocal time.

I wonder if angular momentum transforms the same ?

M

Last edited: Oct 3, 2007
4. Oct 2, 2007

### meopemuk

To be more precise, I think that the rotation period of a moving object should increase by the factor $\gamma = (1-v^2/c^2)^{-1/2}$. Then the rotation speed of such an object should go down, i.e., the factor is $\gamma^{-1}$.

Eugene.

5. Oct 3, 2007

### Mentz114

Agreed. Nothing to it. It's only a kinematic effect in any case. Thanks for the input.