Understanding Different Interpretations of Dynamic Equilibrium

Concept of dynamic equilibrium
The term 'equilibrium' denotes a state at which a system is balanced with no changes occurring internally and externally. However, "dynamic equilibrium" refers to the balanced nature of a system despite the continuously ongoing internal and external processes. This type of equilibrium can be seen in various aspects of life. Here, we expand on the various interpretations of dynamic equilibrium.
Etymology
The word equilibrium is derived from the latin word "aequilibrium", which means "equal balance".
Dynamic refers to constant change, and equilibrium refers to a state of balance. Despite the contradictory nature of these terms, they are paired together to describe a concept observed in complex systems. This concept of dynamic equilibrium refers to a state of balance, in spite of the ever-changing internal and external forces of that particular system. It should not be confused with the concept of stasis, which refers to the absence of any and all change in the system. Stasis is concerned with isolated systems, where no exchange of any parameter is possible, however most systems in nature and in the world are either open or closed systems, which do not necessarily exhibit a state at which there is an absence of change. Hence to these systems, the concept of dynamic equilibrium must be applied.

Though it is widely popular in chemistry and physics, this concept is also translatable to biology, ecology, and economics. It is used to describe complex functions which may appear to be stagnant (unchanging), when in fact are changing when viewed from a different perspective. Another form of dynamic equilibrium is observed, when the input and output values of a system fluctuate around a mean value, with the magnitudes of these fluctuations canceling each other out, thereby giving rise to a natural, dynamic stability. Due to the wide applicability of this concept, it finds applications in various fields of study. Different fields of study offer different interpretations of dynamic equilibrium.
Dynamic Equilibrium in Chemistry
It refers to the state of balance in a reversible reaction system in which the ratio of the products and reactants remain constant, despite the continuous transition of products to reactants and reactants to products. The overall composition of the system does not change and the changes in the concentration of reactants and products are imperceptible. In other words, it means that there is no change in the amount of the reactants and products, despite the continuous occurrence of the reaction.
Example
In case of a sealed bottle of aerated water, two forms of carbon dioxide (CO2) are present. The aerated water is pressurized and bottled in such a way that the partial pressure exerted by the gaseous CO2 is equivalent to that exerted by the water. This water is dynamic in nature, as the gaseous CO2 molecules are continuously getting absorbed by the water, and at the same time the dissolved aqueous CO2 is being converted to its gaseous state. However, this interchange is not seen or observed, since the system itself is stable. The stability would be hampered if the pressure in the bottle was lower or higher than ideal. A lower pressure would cause the bottle to cave in and implode, whereas a highly pressurized bottle would in fact explode.

Dissociation of an acid like HCl in pure water (H2O). In such a case, HCl (l) would dissociate into H+ (aq) and Cl - (aq). While the concentration of HCl remains constant in the solution, there is a continuous interchange between the dissociation of HCl into its component ions and the re-conversion of those component ions back into HCl (l).
Dynamic Equilibrium in Physics
An object is claimed to exhibit dynamic equilibrium when all the forces acting on it are balanced, and the object is moving according to Newton's first and second law of motion. This law states that an object remains at rest or in motion, unless an external force is applied to it, where force equals the product of mass and acceleration (F = ma). Therefore for an object to remain in motion without any external force, it must move with constant velocity, and display no acceleration.
Trolley moving down on slop
Example
In case of an trolley moving down a gentle slope, since the slope is not steep, there is no external acceleration of the trolley. According to Newton's third law of motion, every action has an equal and opposite reaction. This helps explain the balanced forces acting on the trolley and also its motion with uniform velocity. When the trolley is moving along the slope, its weight exerts a force on the slope, which is reciprocated by an equal and opposite force exerted by the slope on the trolley. Since both forces are equal and opposite in nature, they cancel each other out. With regards to the acceleration of the trolley along the slope, the motion causes the generation of a frictional force with a magnitude equal to the acceleration of the trolley. These two forces also cancel each other out, leaving the trolley to move along the slope with no acceleration and constant velocity, thereby displaying dynamic equilibrium.
Dynamic Equilibrium in Economics
The economy shows dynamic equilibrium when the basic economic forces of supply and demand are in a balanced state despite the changing nature of other economic variables such as price, income, quantity, technology, etc. It involves maintaining the balance between the supply and demand despite the constant discrepancies seen between these two variables. It can also be interpreted as the disruption and restoration of the equilibrium state.
Yellow plastic ball in bowl
Example
The concept of dynamic equilibrium with respect to economics could be represented as the placement of a ball in a bowl. Initially, it rests at the bottom of the bowl (equilibrium), but if the bowl is shaken, the ball moves around randomly till it eventually returns to its original resting position, thereby restoring equilibrium. A functional example could be given in terms of the rise in demand for a certain object like potatoes in a stable economy. This rise in demand causes a disruption in the balance between supply and demand. To overcome this, the supply needs to be increased so as to meet and fulfill the increased demand in order to restore the balance between supply and demand, leading to a dynamic equilibrium.
Dynamic Equilibrium in Biology
Every living organism lives in a dynamic state of activity, because of the occurrence of various biological processes required to keep it alive. At any given instant, each cell in the organism's body is in a dynamic state. A stable non-dynamic state is only seen in case of dead cells. Despite this ever-changing nature, a state of dynamic equilibrium is achieved by an organism when all its biological process occur naturally despite the changes in the surroundings of the organism itself.
Cell division stages
Example
The phenomenon of homeostasis can be used to explain dynamic equilibrium in warm-blooded multicellular organisms. Homeostasis is the process by which an organism regulates and maintains its body temperature despite the changing environmental conditions. Another example for dynamic equilibrium is the exchange of various substances between cells. All cells of an organism are surrounded by an intercellular fluid, which contains various ions and elements dissolved in water. The cells are able to absorb the dissolved substance from this fluid, across their membrane. While at the same time, they also release substances into the fluid. This exchange between the fluid and the cells is a continuous process that helps keep the cells healthy and stable. Any imbalance in such a situation would lead to a change in cell stability, eventually resulting in cell death.
Dynamic Equilibrium in Ecology
Ecology is the study of the various ecosystems that occur in nature. Ecosystems cover all the biological organism within a specific geographical area. The survival of any ecosystem depends on the population densities of the various organism, climatic conditions, temperature, precipitation, humidity, soil quality, etc. The stable co-existence of all the biological entities within a system, despite changes in these factors and conditions, give rise to a state of dynamic equilibrium.
Food web
Example
In an ecosystem, populations do not grow unchecked as they are regulated by the populations of other interdependent organisms. This regulation occurs along the connections based on the food chain and food web of that ecosystem. Each higher population preys on the lower population, keeping it in check, i.e. the sudden rise in the population of gazelles would offer a larger population of food source to animals like lions and tigers, thereby keeping the gazelle population in check. In case of changes in climatic conditions, the ability of the organisms to shift their habitat to a more suitable part of the system helps in maintaining equilibrium. Ecosystems usually exhibit different stable states depending on the conditions prevalent, and cyclically switch between these stable states, hence establishing dynamic equilibrium.
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The concept of dynamic equilibrium helps explain the stability in systems, whether biological, chemical, economic, or physical, despite the changing nature of time, and environmental conditions. It can be used to create empirical models to predict the outcome in a scenario defined by specific parameters.