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I understand that the buoyant force is equal to the weight of the air displaced by the volume of the object. I also know that if we had a perfectly solid cube or a hollow cube closed on all sides so that the air inside the cube does not mix with air outside the cube, then the buoyant force will be equal to the weight of the air displaced by the volume of the cube.

However, my question is what will the buoyant force be when the cube is hollow and not covered on all sides, something like shown in this image ...

Hollow

Will the buoyant force be equal to the weight of the air displaced by the volume of the cube, or will it be equal to the weight of the air displaced by the volume of the material used for making the cube.

Sorry if it is common sense or very simple, I am not the most intelligent person.

Thanks very much!

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  • $\begingroup$ Check my answer here: physics.stackexchange.com/q/142697 The buoyant force is proportional to the volume displaced, so in this case, it would be the volume of the 'plates' that build up your box $\endgroup$ – ROIMaison Oct 28 '14 at 10:05
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You may consider the void to be part of your object if you want (and therefore compute the buoyant forces due to the volume). But if you do, you must also consider the weight of the air in that void.

As long as voids are at atmospheric pressure, these two forces will be the same. You'll get the same figure for apparent weight whether they are considered inside or outside the object.

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Actually It will be equal to the weight of air displaced by volume of the walls of the cube or you can say the volume of the material of the cube, since outer air is free to roam in and out of the cube whenever it wants. Sorry to be a bit kiddish. Hope you got your answer.

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