In this paper, we find the solution of the following quadratic functional equation n Sigma(1 <= i <= j <= n) Q(x(i) - x(j)) = Sigma(n)(i=1) Q (Sigma(j not equal i) x(j) - (n - 1)x(i)), which is derived from the gravity of the n distinct vectors x(1), ... , x(n) in an inner product space, and prove that the stability results of the A-quadratic mappings in m-complete convex fuzzy modular *-algebras without using lower semicontinuity and beta-homogeneous property.