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A container has 2 immiscible liquid of different densities. Suppose water on botton and kerosene oil on top. A body floats at the boundary of both such that it is partly in water and partly in the oil.

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Now just consider the force in the upper liquid kerosene. The forces on the side of the body are equal and opposite so they get cancelled. The force acts downwards on the top. I don not understand how does upthrust/buoyancy still happen in kerosene ? There is no surface where it could act in upward direction. Does it acts on the top as a kind of pulling force ? Or along the side where due to adhesive forces the upthrust can act ?

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The layer of kerosene puts pressure on top of the water surface, with the magnitude of the pressure being dependent on the kerosene density and the kerosene depth. That pressure is transmitted throughout the water column via Pascal's law, which increases the pressure throughout the water column relative to what that pressure would be without the kerosene layer. The increased pressure on the bottom of the floating body is what produces enough buoyant force to keep it floating as shown.

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No it dosent,the boyant force is purely due to the upward force due the denser liquid,ot is similar to the case with one liquid,(air being the second fluid in that case) the downward force due to air is less than upward thrust.due to the liquid hence the body float

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It doesn't apply upthrust directly. It does it by adding pressure to the water surface, thereby increasing the upward force that the water exerts at the bottom.

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