How can you prove that atmosphere exerts pressure?

Answer 1

The original experiment that demonstrated this was a portable Mercury column.

If you have a large bowl full of Mercury (a liquid metal) and a 1 meter long glass tube open at one end, then you can make a simple barometer. First, completely fill the tube with mercury, and temporarily close of the open end of the glass tube with a fitted seal, so the glass tube will be completely full of mercury and closed at both ends. Then stand the inverted tube (with its sealed end in the bowl of mercury), and while the end of the tube is immersed in the mercury, remove the fitted seal, allowing the mercury trapped inside the tube to flow into the bowl. Some of the mercury will flow out of the tube into the bowl, but the air pressure will cause the remaining mercury remain in the tube up to a height of (about) 760 mm above the mercury level in the bowl. The volume in the tube above the column of mercury will be filled with a vacuum.

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If you were to then take your portable barometer on a hike up a mountain, you would notice that the volume of the vacuum in the tube would become greater, and the column of mercury in the tube become shorter. This is because the atmospheric pressure keeping the mercury up the tube is lower at a higher altitude.

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Note: Mercury is a dangerous substance and must be handled with care. The above experiment should not be attempted except under the supervision of qualified laboratory personnel.

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