CenterOfMass.cs

public static class MathHelper
{
    public struct MassPosition
    {
        public Vector3 position;
        public float mass;
    }

    public static Vector3 CenterOfMass(List<MassPosition> massPositions)
    {
        float massSum = massPositions[0].mass;
        Vector3 center = massPositions[0].position;
        for (int i = 1; i < massPositions.Count; i++)
        {
            MassPosition mp = massPositions[i];
            float summ = massSum + mp.mass;
            center = (center * massSum + mp.position * mp.mass) / summ;
            massSum += mp.mass;
        }
        return center;
    }
}