Final answer:
When forces are not in equilibrium, an object experiences acceleration or deceleration due to the unbalanced net force, which can be affected by variables such as pressure and volume or resulting from displacement from equilibrium states.
Step-by-step explanation:
When forces are not in equilibrium (unbalanced), the object can be described as experiencing acceleration or deceleration, and its state of motion is changing. Forces acting on an object result in a net force, which according to Newton's second law is equal to the rate of change of the momentum of the object. External, macroscopic variables such as pressure and volume can influence an object, causing it to move against an opposing force.
A system in unstable equilibrium will experience a net force or torque in the same direction as the displacement from equilibrium, potentially leading to increasing acceleration away from the equilibrium position. In contrast, a system in neutral equilibrium maintains its state regardless of such displacements.
It is important to note that the net external force on a system can be non-zero even when its speed remains constant, as illustrated by an object moving at constant speed in a circle. Here, the unbalanced force is the centripetal force required for circular motion.
In interactions within a closed system, the total momentum is conserved, but kinetic energy may not be. For example, when forces are applied to an object such as an ice hockey stick, even if the net external force of the system is zero, the system may not be in equilibrium if there's rotation or if forces are not evenly distributed.
All objects naturally tend towards a position of minimum energy unless external forces are acting upon them. A force pushes or pulls an object and arises from an interaction between two entities; it does not exist independently. This explains why for every action, there is always an equal and opposite reaction, maintaining the momentum of the entire system.