From the engineering point of view, all structures are subjected to dynamic actions. If acceleration is zero, these actions become static and therefore the mass won't be considered.

Dear Ahamed,

y=ax is an static equation if it represent a process this one is static.

In the opposite sens y=dx/dt or any other differential equation this is an dynamic equation and representation are also dynamic.

All dynamic process after passing by transient time then becaming static process.

Best regards

A system is dynamic if its behavior at a given instant depends not only on the present inputs but also on the past inputs. A dynamic system is said to have memory or inertia. A dynamic system is most often described by one or several differential equation, one or several difference equations, one or several algebraic equations with a time lag.

In a static system, the state and the output at a given instant depends only on the input at this instant. The relation between the input and the output is then given by one or several algebraic equations. If a static system does not have memory, it does not mean that it does not evolve over time. We can see that the output y(t) of the static system y(t) = 5u(t) evolves proportionally to its input u(t).

You may want to check my post elsewhere at this forum ― as a case study related to transient mass balance analysis:

https://www.researchgate.net/post/Hello-everyone-can-you-please-help-me-answer-this-questionWhat-is-the-steady-state-concentration-of-the-toluene-in-the-individuals-vascular-system