Terminology of different equilibria?

Question

I've heard many equilibrium terms:

1. Translational equilibrium
2. Rotational equilibrium
3. Static equilibrium
4. Dynamic equilibrium

The different terminology is slightly confusing. My understanding is as follows:

Translational equilibrium refers the equilibrium position when the resultant force is 0. Rotational equilibrium is when the net moment on an object is 0. An object could be in translational equilibrium without being in rotational equilibrium if the forces act on different lines of action.

Translational equilibrium encompasses the terms static and dynamic equilibrium. Static equilibrium is when the net force is 0. However the object remains at rest. Dynamic equilibrium is when the net force is 0. However the object remains in motion.

Is this correct?

Answer 1

As you have shown, there are many types of equilibrium, I will answer all four which you mentioned.

First of all, What is Equilibrium in general?

Equilibrium

In simple words, equilibrium is a state of balance due to the equalaction of opposing actions. In other words, when two or more opposing actions are performed on something in such a way that the net effect of the actions is zero.

Types of equilibrium (in physics)

Out of all kinds of equilibrium, four which the question asked are:

$1.$ Translational Equilibrium: When net forces on a body or a system of bodies is zero i.e. $\vec{F_{net}=0}$, then the body or system is in Translational Equilibrium. In this case, acceleration of the center of mass is zero $\vec{a_{com}}=0$. Therefore the center of mass of body/system will not change its velocity, which also means that it will not change its state of rest or motion in translation.

$2.$ Rotational Equilibrium: When net torque(rotational equivalent of force) on a body or a system of bodies is zero about all points i.e. $\vec{\tau_{net}=0}$, then the body or system is in Rotational Equilibrium. In this case, angular acceleration (rotaional equivalent of acceleration) of the system about all points is zero $\vec{\alpha}=0$. Therefore the body/system will not change its angular velocity.

$3.$ Static Equilibrium: In physics, when net forces and torque on a body/system is zero and the body/system is at rest which means no individual components of the system are in motion, then the body is in static equilibrium.

$4.$ Dynamic Equilibrium: In physics, when net forces and torque on a body/system is zero but individual components of the body/system are in motion, infact individual components might even have acceleration, but as a system its net acceleration would still be zero,then the body is in dynamic equilibrium.