Gas pressure requires a container
Flat Earthers like to claim that gas (specifically the gas in Earth’s atmosphere) can only exert pressure if it is contained by some tangible, airtight barrier, often citing the Second law of thermodynamics as the reason for this. The argument is used to imply the existence of a firmament that contains the atmosphere.
Common adages include:
Gas pressure requires a container
You can’t have gas pressure without a container
The necessary antecedent to gas pressure is a container
[1]Gas pressure is defined as gas molecules pressing against the walls of the container
[note 1]
Of course, Earth is sufficiently massive for gravity to contain the atmosphere. Many flerfs think that gas isn't affected by gravity, but this is incorrect. Gas has mass and is affected by gravity just as much as any other form of matter. In a gravitational field, gas settles into a pressure gradient such that the upward force due to pressure differences perfectly balances the downward force due to gravity. This pressure gradient is observed in the atmosphere and is easily measurable, even with a mobile phone app. Contrary to popular belief, the gradient is not necessarily caused by the fact that gravity is weaker further from Earth's surface.
If the firmament were exclusively responsible for containing the atmosphere, there would not be a pressure gradient. Instead, air pressure would equalise everywhere. Even if the firmament were real, it would not be what is containing the atmosphere.
Vacuum
Flerfs often make the mistake of thinking that vacuums pull things towards them. This is because we intuitively think of "sucking" as a pulling force, when in actuality, it is the pressure of a substance that pushes it towards free space. Vacuums are simply regions that are devoid of matter. They don't create forces and don't have any kind of "sucking power". Most if not all of outer space is only an approximate vacuum; even interstellar space contains around one atom per cubic centimetre.[2] This equates to about 1×10-17 torr.
Housekeeping question
The afformentioned pressure of interstellar space led to the famous housekeeping quesion, "is 10-17 a negative number?". Flerfs have struggled to answer this.
Second law of thermodynamics
See also
Notes
- ↑ Air exerts pressure on anything it comes into contact with, not just the walls of any container.