Weight of Water Related to the Weight of Air

The theoretical atmospheric pressure at sea level (14.7 psi) will support a column of water 34 feet high:

weight of air 14.7 psi x 2.31 ft/psi = 33.957 ft, or 34 ft

At an elevation of 1 mile above sea level, where the atmospheric pressure is 12 psi, the column of water would be only 28 feet high: 12 psi x 2.31 ft/psi = 27.72 ft, or 28 ft

If a tube is placed in a body of water at sea level (e.g., a glass, a bucket, a water storage reservoir, lake, pool), water will rise in the tube to the same height as the water outside the tube. The atmospheric pressure of 14.7 psi will push down equally on the water surface inside and outside the tube. However, if the top of the tube is tightly capped and all of the air is removed from the sealed tube above the water surface, forming a perfect vacuum , the pressure on the water surface inside the tube will be 0 psi. The atmospheric pressure of 14.7 psi on the outside of the tube will push the water up into the tube until the weight of the water exerts the same 14.7 psi pressure at a point in the tube even with the water surface outside the tube. The water will rise 14.7 psi x 2.31 ft/psi = 34 feet. In practice, it is impossible to create a perfect vacuum, so the water will rise somewhat less than 34 feet; the distance it rises depends on the amount of vacuum created.


Author: T.P.Sivanandan

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