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There is a beaker of water with ice floating on top of it. If I add oil (lighter than water and ice) to it such that it forms a layer above water and ice is suspended between those layers. Does the ice rise or fall from its previous level?

specific gravity of ice = 2/3 specific gravity of oil = 1/2

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  • $\begingroup$ Please be more specific. Some oils have a density greater than that of water. What is the density or specific gravity of the oil? Also, "Does the ice rise or fall from its previous level?" ... its previous level in water, or its new level in oil compared to its previous level in water with no oil? $\endgroup$ Commented May 2, 2019 at 18:47
  • $\begingroup$ @DavidWhite It says "lighter than water and ice". I think it's safe to assume that is referring to the relative density. $\endgroup$
    – JMac
    Commented May 2, 2019 at 18:49
  • $\begingroup$ I still need the specific gravity of the oil. That specific gravity could be more or less than that of ice. $\endgroup$ Commented May 2, 2019 at 18:51
  • $\begingroup$ @DavidWhite Suppose specific gravity of oil is 0.5. $\endgroup$ Commented May 2, 2019 at 18:52
  • $\begingroup$ @DavidWhite Again, I assume "lighter than water and ice" was more to due with density than it was the net mass. $\endgroup$
    – JMac
    Commented May 2, 2019 at 18:52

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Whenever an object is immersed in a fluid (including air), there is a buoyant force on that object that is equal to the weight of the fluid that is displaced, according to Archimedes' principle. Thus, the ice cube in the water is floating at the level whereby the weight of the water and air that it displaces is equal to the weight of the ice cube.

When you add an oil to the beaker that floats on the water, the ice cube is now displacing some of the oil that surrounds it, and there is a buoyant force on the ice cube that is equal to the weight of the water and oil that it displaces. Since the oil is floating on top of the water, it takes the place of air that was formerly on top of the water. The weight of the oil that is displaced by the ice cube is greater than the weight of the air that was displaced by the ice cube, so the ice cube will rise in the water until the weight of the oil that is displaced plus the weight of the water that is displaced once again equals the weight of the ice cube.

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  • $\begingroup$ Great explanation. I was getting a sort of hunch that this would happen, but could tell myself exactly why. Well explained sir. $\endgroup$ Commented May 2, 2019 at 19:18

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