B Atmospheric pressure, vacuum, etc.

[tomlib]

The value of the atmospheric pressure does not seem to me to be correct 1013 HPa and can be recalculated as approx. 1kg/cm2 (is it true?), but it does not seem that such a pressure would be manifested by any resistance or any deformations, for example on a folded sheet of paper. It is possible that this value is derived from the creation of a vacuum. Is possible, that the cause of the great force of vacuum is due to something other than the pressure of the surrounding air, which appears to be normal without resistance? How is it possible that if there is a vacuum in space, the air from the Earth is not drawn into space?

How will the vacuum value actually change in different sized vessels or on different sized surfaces.

 

[Dale]

Is possible, that the cause of the great force of vacuum is due to something other than the pressure of the surrounding air, which appears to be normal without resistance?

Probably not, but it is hard to tell what you mean by this. Pressure is well-understood.

How is it possible that if there is a vacuum in space, the air from the Earth is not drawn into space?

Gravity pulls it down.

 

[FranzS]

Loosely speaking...
Vacuum is just the absence of air, and it does not "pull". It is really air that "pushes". You don't see the effects of the relatively high "pushing force" of the atmospheric air because for the most part it is counter-balanced (for instance, fluids inside the human body are at the same pressure of external air and won't allow the latter to make us implode).

 

[hmmm27]

Is possible, that the cause of the great force of vacuum is due to something other than the pressure of the surrounding air,

No.

Occasionally you'll run across a reference to "inches of vacuum" or something like that, but those are actually just offsets of outside pressure, used for convenience.

 

[tomlib]

Gravity pulls it down.

I would say that the force of the vacuum is greater than the force of gravity.

 

[Dale]

I would say that the force of the vacuum is greater than the force of gravity.

You can say it all you want, but the simple fact that we do actually have an atmosphere proves your saying wrong.

 

[tomlib]

You can say it all you want, but the simple fact that we do actually have an atmosphere proves your saying wrong.

Okay, thank you then.

 

[jbriggs444]

I would say that the force of the vacuum is greater than the force of gravity.

The two do not have the same units. So neither is greater than the other.

The "force of gravity" is in units of force per unit mass. For example, 9.8 Newtons per kilogram. The "force of vacuum" is in units of force per unit area. For example, 100 kiloNewtons per square meter.

If you want to compare the two to one another, you will have to somehow figure out how many kilograms of atmosphere there is in a square column that is 1 meter on each side and is as tall as the atmosphere.

An overly simplistic calculation would assume an atmosphere which has constant density from top to bottom. Let us attempt such a calculation.

Room temperature air at ordinary atmospheric pressure is about 1.293 kilograms per cubic meter. The atmosphere is, let's say, 100 kilometers in height. Our square tower has a volume of 1x1x100000 = 100000 cubic meters. So that is 129300 kilograms. Multiply by the acceleration of gravity (9.8 Newtons per kilogram) and that's roughly 1.3 million Newtons.

The "force of gravity" on one square meter calculated this way is 1.3 million Newtons.
The "force of vacuum" on one square meter is only about one hundred thousand Newtons.

Calculated this way, the "force of gravity" is way larger than the "force of vacuum". Contrary to your supposition.

But of course, the above calculation is wrong, wrong, wrong. Atmospheric pressure decreases as you go up in elevation. Wikipedia goes fairly deep into the details. To a decent approximation, there is an exponential decrease in density with altitude. The constant on the exponential is about 8.4 km for a factor of e (Euler's number, base for natural logs, 2.71828...) reduction.

As a rough rule of thumb, this means that the actual amount of atmosphere over any point on the earth is equivalent to a tower of normal pressure air that is 8.4 km in height. Yes, the same 8.4 km as above -- natural logs are nice for this kind of thing.

Let us do that calculation again. 1.293 kg per cubic meter times 8.4 km height times 9.8 N/kg is roughly 101000 N / m^2 for the "force of gravity"

Conclusion: The force of gravity and the force of vacuum are indeed identical. As they must be according to the mainstream understanding of an atmosphere in static equilibrium under gravity.

Edit: Here is the source for the 8.4 km figure:

The pressure can be approximated by another exponent:
[...]

[...]
H_p is 8.4 km,

$H_p$ is the inverse of the $\frac{gM}{RT_0}$ in the formula above.

 

[russ_watters]

I would say that the force of the vacuum is greater than the force of gravity.

That's silly. Vacuum is the absence of force (atmospheric pressure).

You've started multiple threads and your tone and approach are very strange. You are arguing against explanations of reality based on incredulity alone. Basically arguing that reality itself is wrong. It makes no sense. Accept that reality is reality and then learn the explanations for it. Asking questions like "I don't understand how..." is fine, but making counterfactual claims is not. It won't help you learn and it is an approach we will not humor indefinitely.

 

[russ_watters]

We do get questions like this occasionally, but people tend to overcomplicate it. It's no different from pressure at the bottom of a pool (after subtracting atmospheric pressure), a stack of books on a table or a pile of anything on the ground. For the sake of pressure at the bottom or, roughly, its mass, the atmosphere is just a "pile of air" sitting on the ground.