Static equilibrium is when resultant force and resultant moment equals to zero
Any static force system will be in equilibrium if the resultant force and resultant moment both are equal to zero.
Static equilibrium can be expressed as
ΣFx = ΣFy = ΣFz = 0 (1)
ΣMx = ΣMy = ΣMz = 0 (2)
F = force (N, lb)
M = moment (Nm, ft lb)
x, y, z = orthogonal axes