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## Summary:

- Second and Third Newton Law

## Main Question or Discussion Point

Hi, I am brainstorming about Dark Energy.

Lagrange–d'Alembert principle is stating that sum of external forces on the system of rigid bodies and sum of system forces must be in quasi static equilibrium.

What if there are no external forces acting on system of bodies and vector summation, relative to fixed reference frame of all m*a in the system of bodies is not equal to zero; would d'Alembert principle still hold?

Lagrange–d'Alembert principle is stating that sum of external forces on the system of rigid bodies and sum of system forces must be in quasi static equilibrium.

What if there are no external forces acting on system of bodies and vector summation, relative to fixed reference frame of all m*a in the system of bodies is not equal to zero; would d'Alembert principle still hold?