I want to understand the factors and terminology associated with pressure in the following scenario. I have a balloon filled with water. Inside this balloon is an irregular vessel, say a corked glass test tube, also filled with water. I can poke and squeeze the balloon with impunity, knowing that, due to the nature of incompressibility of the water both outside and inside the test tube, it is immune to breakage. Furthermore, unless the balloon is transparent, I might not even know there is anything floating around inside. It is immune to my poking and probing. Now I open the balloon, and let 90% of the water out. It is now quite easy to conform the balloon to the test tube and even feel the test tube within the balloon. If I now squeeze the balloon, I am in great danger of breaking the test tube because it will now experience forces directly from my hands against its irregular shape. I wish to use the correct terminology to apply to these two scenarios when it comes to pressure and forces. i.e. in terms of pressures and forces, why would one say it is better for the test tube to have the balloon filled with water?