# Stress of a Rod with angular velocity

1. Aug 26, 2014

### Chacabucogod

As far as I understand a rod that has an angular velocity is static. Nonetheless, if we analyze a particle in the rod, this particle will be subject to a centripetal force that will be proportional both to the angular force and radius. Now I understand that the external forces and momenta exerted on the rod are zero; thus, it's static.

How does one take into account that the bar is suffering certain stress due to rotation? How is it calculated? Is it really static? I understand those forces are internal, but those are the forces that are studied in a class like strength of materials right?

Thanks a lot for taking the time to answer my question.

2. Aug 27, 2014

### Simon Bridge

A bar is not classically rigid - it is made up of atoms joined by those squishy electromagnetic forces, so it can stretch. You can model one as a line of small ideal masses joined by small ideal springs. Can you see that rotating such a structure will stretch the springs - hence, tension?

Is the bar static? Every part off-center is acted on by an unbalanced force after all.
The unbalanced forces come from the internal forces binding the atoms together. Another effect of those forces is the material strength you studied in class.