Can free body diagrams be used if friction at pivot is not negligible?

[macardoso]

TL;DR Summary

See title?

Are we allowed to use free body diagrams in dynamic systems where there is non-negligible friction in say the rotational pivot between two linkages? If so, how to incorporate friction into the equations of motion? If not, what method allows friction to be accounted for?

 

[Nugatory]

Are we allowed to use free body diagrams in dynamic systems where there is non-negligible friction in say the rotational pivot between two linkages?

Sure, it's just another force. It is a bit tricky at a rotational pivot because there will be a torque as well as a force, but if you're comfortable working with torques around an idealized frictionless pivot you'll be able to introduce the effects of friction naturally.

 

[macardoso]

Sounds good, I'll work on this on my own, and I might post back for clarification on my specific case in the future. Thanks!

 

[cjl]

Note however that it's likely (or at least possible) that you'll end up with an indeterminate solution, as there could easily be more than one statically balanced set of forces and moments that could result in the final situation. Frictionless pivots are often a simplifying assumption that is necessary to achieve a single unique result.