# Inertia and equlibrium of machines

1. Sep 19, 2008

well, i would like to ask abt sth we studied in theory of machines ' we studied chapter named(equilibrium of machines) but i am really so confused abt concept of this equilibrium
because in this chapter we have studied that any part of machines under equlibrium
u can apply these equations to it
(1)f=ma
where f is inertia force
(2)inertia torque=mass x angular acceleration
and i think for any object under any forces u can apply newton's second law on it
total forces= ma where (ma is the inertia force) so i understand from this equation that this part of machine comes to equilibrium due to its inertia force
well,my question here is that every object is under inertia force when some forces acts on it so any part of machine will be in equilibrium even without calculations i know this maybe wrong but i cant find interpretation

this maybe because i have misunderstanding abt concept of equilibrium like sometimes iam asking when part of machine not in equilibrium ?what happens to it if it's not in?sth like that
or maybe i ve problem abt concept of inertia force or inertia torque

but really i am so confused abt the equations above every object or every part of machine will be in equlibrium ???even without calculations???

2. Sep 19, 2008

### Topher925

I had a bit of a hard time understanding your post. If you could re-write it with out so many short handed works and better structure I could probably better understand what your asking. Anyways, I'm going to assume that you are confused about how the torque on a electrical machine is calculated. A simple model use for the armature for most machines is:

Tm = Te + fw + Ja

Where:
Tm = mechanical torque
Te = electromagnetic torque
f = friction coefficient (not always linear)
J = moment of inertia
a = acceleration

If an equilibirum state is obtained that usually means that there is no acceleration of the armature (a = 0). Because of this the only forces acting on the armature are the loading torque (Tm), the electromagnetic torque (Te) and the force of friction (fw). In other words, in equilibrium

Tm = Te + fw