Release Message: Even though hydrometers are used to measure fluid density, a hydrometer will not indicate changes of fluid density caused by changing atmospheric pressure.
Description: The elevator paradox relates to a hydrometer placed on an "elevator" or vertical conveyor that, by moving to different elevations, changes the atmospheric pressure. In this classic demonstration, the floating hydrometer remains at an equilibrium position. Essentially, a hydrometer measures specific gravity of liquids independent of barometric pressure. This is because the change in air pressure is applied to the entire hydrometer flask. The submerged portion of the flask receives a transmitted force through the liquid, thus no portion of the apparatus receives a net force resulting from a change in air pressure. This is a paradox if the buoyancy of the hydrometer is said to depend on the weight of the liquid that it displaces. At a higher barometric pressure, the liquid occupies a slightly smaller volume, and thus more dense might be considered to have a higher specific gravity. However, the hydrometer also displaces air, and the weight of the liquid and the air are affected equally by elevation.