A friend and I debated what is the 'stronger' structure: a hollow (fluid filled) metal sphere or a metal sphere with one or more metal cross beams that span the sphere diagonally given that the same quantity of material is used in both. By 'stronger' I mean the resistance to compressional forces involved in submerging this structure in a fluid such that there is a pressure difference between the inside and outside of the sphere. Initially we assumed the simple plain hollow sphere since a fluid should exert an equal force over the entire surface. However, for a larger sphere immersed in a fluid that's in a gravitational field, the 'top' of the sphere will experience less pressure that the 'bottom' of the sphere. But presumably the fluid inside the sphere would have a similar pressure gradient since it is in the same gravitational field. We were still leaning in favour of the plain hollow sphere when we wondered how robust it would be should the fluid it's immersed in have sound waves with large amplitudes moving through it, or when it impacted a solid surface, or found itself at the interface of two stratified fluids. That's when the debate became more animated: I insisted that a structure like a bone matrix in the sphere would be best while my friend stuck to the plain hollow sphere.