Keywords:Equilibrium, thermodynamic, mechanical, spontaneous
This article is about equilibrium in a thermodynamic sense.
An absence of unbalanced force in the interior of a system, or between the system and the surroundings, implies mechanical equilibrium. Non fulfillment of this condition causes changes, both in the system and in the surroundings in general, which cease only when the mechanical equilibrium is restored
Thermal physics —A.B. Gupta , H.P. Roy