What is meant by "the pressure of the atmosphere"? What causes this pressure?

1 Answer
Apr 23, 2016

Atmospheric pressure is essentially the pressure of the weight of the atmosphere.

Explanation:

Over any given point on the Earth you have a column of air rising to the top of the Thermosphere at about 500 miles(ish). Even though we don't think of the air as actually having weight, it actually weights quite a bit. If you had a vacuum tube with an open end in a lake the pressure of the atmosphere on the surface of the lake would be enough to push water over 30 feet up that tube. Which is why barometers use mercury. Mercury is much heavier and so the weight of the atmosphere only pushes the mercury about 30 inches up that tube.