Originally Posted by
Derfred
What a fascinating question.
I like to think about it this way. The atmosphere exerts a certain force on the surface of the earth. That force is caused by gravity pulling on the mass of the atmosphere. This is known as the weight of the atmosphere. It is this weight that causes sea-level atmospheric pressure to be what it is.
Not exactly.
Consider a water bottle with broad bottom and tall neck, which is full of water.
The water pressure on the bottom is high, and over the wide bottom sums out to a large force. Yet the weight of the water column in the tall but narrow neck does not sum up to so much.
The matter is that the water also exerts pressure on the upper part of the bottle, below the neck. That force is applied down to the water, and transferred to the bottom.
Likewise, if there is something pressing on air from above, such as a landed plane taking up volume from atmosphere but resting on wheels, thatīs extra air pressure which need not be weight of air.