Is an unchanging two star orbiting system in equilibrium (force wise)?

sophiecentaur

I think that the classical approach would assume that, in equilibrium, you couldn't detect any acceleration. In the case of a rotating planet, because of the varying 'weight' forces for someone on the surface, they would detect acceleration change and I would say they would, in their own frame of reference, 'know' they were not in equilibrium. But, from another frame, it would be clear that they are constantly accelerating hence not in equilibrium.

I guess it's down to a more strict definition of the term than I'm capable of giving. It's been mentioned already that the term 'equilibrium' has different meanings in different situations.

mikeph

By the definition we learnt, equilibrium = all forces cancel/no net force.

sophiecentaur

No net force on what? - is the point. We all know that simple definition of equilibrium but I though we were exploring the various aspects of the system where equilibrium could be said to apply.
We could say that no energy is being exchanged with the system - so there is no work done on it and so the forces on the whole system must be in equilibrium. Looking at one of the pair, there is acceleration, whatever orbit, because there is motion in a curve. There must be unbalanced forces so No Equilibrium. But would the star detect any acceleration / force (if it could see no more than its partner star. Would the star think it was in equilibrium?
etc. etc. different considerations (reference frames) yield different conclusions.

mikeph

It just seems very backwards to me to think of a word, then explore what it could mean. I don't see how the process could be anything but pure semantics.

sophiecentaur

You could look at it that way. Or you could take it as a sign that the message doesn't always get across because of the terminology used. We could always have a Forum Glossary, I suppose and then demand that all posts use only the strict definitions in it. Could be hard to police, I suspect.
We are divided by a common language, as they say.