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Introductory Physics Homework Help
Finding downward force on immersed object
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[QUOTE="kuruman, post: 6866976, member: 192687"] As you contemplate answering [USER=334404]@haruspex[/USER]'s question in post #32, also think about your BFD in post #19. It shows two forces directed down and one force directed up. In post #27 you claimed If that is indeed the case, then you should agree that the correct FBD should show two forces directed up (mesh and fluid) and one directed down (Earth.) Remember, that you should draw one arrow for each entity exerting a force. So let's see you post a correct FBD with 3 arrows, 2 up and 1 down labeled with the names of the entities that exert the forces represented by these arrows. To help guide your thinking, I show below a FBD of the block of fluid in the figure from post #3. There are two entities exerting a force on this block, Earth (down) and Fluid (up). It says that "water floats on water" and that the two forces have equal magnitudes and opposite directions. If I label the force exerted by the Earth ##mg## and the force exerted by the fluid ##BF##, it follows that ##BF=mg.## Note that, for this particular situation, the force exerted by the fluid is the sum of an up force exerted by the fluid at the bottom of the block, ##F_B=p_BA## and a down force exerted by the fluid at the top of the block, ##F_T=-p_TA.## The single arrow representing the net force exerted by the fluid on the block is the sum of the two which is called the buoyant force, ##BF=p_BA-p_TA.## [ATTACH type="full" width="148px"]323780[/ATTACH] For some reason that I do not understand, your professor and/or your TA impressed upon you that ##F_T## is important in the analysis of your experiment. In my opinion it is not and I think [USER=334404]@haruspex[/USER] agrees with me. I recommended that you abandon ##F_i## and ##F_j## because they only serve to confuse you and prevent you from seeing clearly what is going on. Their usefulness extends no further than the derivation of the Archimedes principle, namely that the buoyant force is equal to the weight of the displaced fluid. That's all you need to draw correct FBDs related to floating or immersed objects as in the case of your experiment. [/QUOTE]
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Finding downward force on immersed object
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