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Mechanical Engineering
Why do you feel heavier in water?
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[QUOTE="potto, post: 6851429, member: 58728"] [ICODE] Because its fixed volume, a brick submerged in water displaces a unique mass of water, being moving or not. When forced to move along a horizontal line, it offers different resistance (or drag) depending on the position in which it is forced to move. [/ICODE] The first statement is correct and I agree with it. The second part is not correct. The direction of the movement is irrelevant to the drag (only the oreintation of the body) . However, the gravity has effect on the forces (or the acceleration). [ICODE] How can that be if, according to the added mass idea, when the brick is forced to move through the water, it pushes exactly the same mass of water in front of it than the mass of water that has to fill the space where the brick was before [/ICODE] This concept is called mass conservation. The pushed fluid push other fluid ending by filling the last place. You can think about as a chain (it is not really) as this description make it easier to visualize the phenomenon. [ICODE] Regardless the path the water has to flow through, the same mass of it has been forced to moved. This mass depends solely on the volume of the brick times density of water. [/ICODE] Not exactly correct. The amount of water that has to flow depends on the shape of body and the boundaries (shape) of the box. Thus, thus mass depends on the volume of the body, shape of the body and density of the block (and orientation). I saw in the book a table describing the different shapes with different coefficients. I think that he got the information from other references like this one (see in the references in the book) People have to find value of the added properties from experiential work. For example, (Aso, Kan, Doki, and Mori 1991; Brennen 1982; Molin, Remy, and Rippol 2007) I just google Brennen and fund this link. [URL]https://apps.dtic.mil/sti/citations/ADA110190[/URL] From what I see there is a long list bodies. Also from what I see this ref was at one point classified information by USA. [ICODE] Could we conclude then that the resistance to movement (or drag) depends on the shape in which the submerged object faces the movement? [/ICODE] yes, the movement direction affects the added mass and also the resistance but it is not related. [/QUOTE]
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Why do you feel heavier in water?
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