Dear Colleagues,

We often incorrectly figure that equilibrium means a static ‘we-have-arrived-in-a-state-of-peace’ state. Nothing could be further from the truth. Equilibrium represents an active and dynamic balancing act. At all times. This came home to me in a recent study on thermodynamics I did with an object in a heat bath. Although both object and heat bath seem to be in equilibrium at the same temperature, they are nonetheless still exchanging heat with each other.

Think of Chemicals
When two chemicals are mixed (and react) forming a new product, the reaction may appear to come to an end after a while. We think of this final state as equilibrium. But often the mixture remains active where portions of the product ‘uncombine’ back into reactants and reactants continue to combine into the new product. There is a constant movement between the reactants.

Structural Equilibrium
Similarly with structural equilibrium where everything is deceptively unmoving. The structural element works continuously and vigorously in dealing (‘resolving’) the various forces impacting on it to produce an overall (resultant) force of zero. Without a neat zero resultant force, the object will move - often with disastrous results. You only need to think of the recent mudslides where everything was happily in equilibrium for thousands of years and now has decided to move.

What Is the Take Home Message from All this?
When you look at something in equilibrium – no matter whether it is a structural element or chemical or even people seemingly in equilibrium – remember that it is a dynamic state and always consider what could cause the equilibrium to be disturbed.  You may be horrified to find that seemingly stable systems in equilibrium are very close to breaking away from equilibrium with disastrous consequences.

Thanks to 101 Things I learned in Engineering School by John Kuprenas with Matthew Frederick.

Mark Z. Danielewski remarked: “Physics depends on a universe infinitely centred on an equals sign.”

Yours in engineering learning,

Steve

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