Torricellian barometer, atmospheric pressure, and the rest

[Aaron Mathis]

Has anyone here given much thought or had much training in regards to
barometers and the relationship they have to thermometers? I'm trying to understand how atmospheric pressure effects the resting level of a liquid and I don't feel quite right about how I see it. I'm wondering why temperature doesnt play an equally significant role in barometers, or if it does.

Come on ya'll - - let's teach Mathis a thing or two.

Barometer (from http://www.infoplease.com

Barometer (burom'utur) [key], instrument for measuring atmospheric pressure. It was invented in 1643 by the Italian scientist Evangelista Torricelli, who used a column of water in a tube 34 ft (10.4 m) long. This inconvenient water column was soon replaced by mercury, which is denser than water and requires a tube about 3 ft (0.9 m) long. The mercurial barometer consists of a glass tube, sealed at one end and filled with pure mercury. After being heated to expel the air, it is inverted in a small cup of mercury called the cistern. [snip]

It's hard to picture how they managed to do this in the 17th century without getting air bubbles into the tube, isn't it?

article continued: The mercury in the tube sinks slightly, creating above it a vacuum (the Torricellian vacuum).

Has anyone thought much about what is theoretically contained in such a vaccum? I know that by definition there is nothing, but I think the truth is that there is always a plenum of energy no matter where you are, just a different type.

Atmospheric pressure on the surface of the mercury in the cistern supports the column in the tube

In other words; atmospheric pressure stops the mercury from decreasing down the tube to such an extent that it flows out of the cisturn and onto the floor.

Is that a good way of putting it?

The level that the column of mercury is at varies in height according to variations in atmospheric pressure. Hence changes in elevation affect the level that the column of mercury rests at. The column of mercury generally decreases in height as you climb above sea level

Ok, so they seem to be saying; the higher you go above sea level, the more the mercury level decreases down the tube, and this is because the air weighs less. Because the air weighs less, the mecury is allowed to relax a bit more. The mecury level goes down in the tube, only because the mercury level in the cisturn goes up. Right?

Can you go so high up that the cisturn overflows ? Gravity of course would stop it from emptying out completely

Also, at colder temperatures, does a body of liquid like mercury actually shrink in overall resting height?

The reason I ask is because, when I look at a thermometer, the mercury rises when it gets hot. Is this because the body of the mercury as a whole is expanding? And does the mercury decrease when it's cold becaues its body as a whole is constricting, becoming more dense?

Thermometers seem significantly different than barometers because they are totally sealed off and therefore the weight of air cannot cause the mercury to rise or fall.

Am I on the right track here folks?

What I'm further confused about is why the barometer is not seriouly affected by temperature as well as atmospheric weight.

Standard sea-level pressure is 14.7 lb per sq in. (1,030 grams per sq cm), which is equivalent to a column of mercury 29.92 in. (760 mm) in height; the decrease with elevation is approximately 1 in. (2.5 cm) for every 900 ft (270 m) of ascent.

At a given location a storm is generally anticipated when the barometer is falling rapidly; when the barometer is rising, fair weather may usually be expected.

Why does air weigh less when a storm is building up? Why does the air weigh more during times of peace?

- Mathis

[Aaron Mathis]

Aaron wrote:

Why does air weigh less when a storm is building up? Why does the air weigh more during times of peace?

Seriously though folks. It seems pretty counter intuitive.

You would think that a storm brewing would mean extra moisture in the air, and thus heavier air and thus a higher reading on the barometer.

During fair weather, there would be less moisture in the air, and thus you would have a lower barometer reading.

But that's wrong.

So what is right and why?

[Elizabeth Isabelle]

Air is a fluid. When the fluid gets stirred up, storms happen. The storms go to the areas of lower pressure because the areas of higher pressure won't let them in so easily.

If the fluid didn't get stirred up in the first place, there wouldn't be a storm, and the pressure would be equal - like it is during peaceful times. The lower pressure before/during a storm is an unnatural low.

Here: maybe this site will help you with all of your weather questions:
http://www.noaa.gov/

[BMcGilly07]

If I remember correctly, the following is a formula used for a single specific molecular gas, and probably has only a general correlation to the movements of huge atmospheric masses:

P*V=n*R*T
Where, P is pressure, V is volume, n is number of moles, R is the constant for the given gas in question, and T is temperature.

That's the extent of my knowledge regarding pressure and temperature, just a plug n' play formula, which only works in a closed system. I'm not too keen on science, but in my experience here in the northeast of America, storms gather most often when a cold front moves in and collides with a warm front.

Looking at the formula above, which is used for one given gas in one given amount, we see that a decrease in temperature would decrease the volume of the atmospheric gas, thus increasing the pressure.

[Aaron Mathis]

Air is a fluid. When the fluid gets stirred up, storms happen.

What causes the air to get stirred up Eliz? Using fluid as an analogy for air is helpful. I picture how a paddle, when you stroke it through the water, it often creates a whirl-pool. In regards to the massive ocean of air, what can we imagine as the paddle stroking through it creating storms?

The storms go to the areas of lower pressure because the areas of higher pressure won't let them in so easily.

I think you are on the right track here Elizabeth. Please consider my latest wonderings:

I wonder if a storm flees, or is squeezed out from the area where it was created?

Kind of like flatuence emits out from the higher pressure conditions of the ass, making a stink?

The totality of the genius forum can be seen as kind of a big storm, squeezed out from the high pressures within individuals.

Perhaps storms are thrown down into a particular area by the very high pressure forces that created it.

Kind of like rebellious teenagers who gather in destructive groups.

They are gathering in low pressure areas, because they can’t tolerate the higher pressure that is felt in the presence of the parental forces.

How does this sound to the G-forum crew? Are these jewels I am unearthing or what?

In my experience here in the northeast of America, storms gather most often when a cold front moves in and collides with a warm front.

Bryan! Thank you for participating in my thread!

Please consider my reply:

Does the storm gather where the two forces collide? Or is the storm created by to colliding forces, yet is repelled by the very forces that created it, seeking an area where it can relax and be itself. The further the storm drifts from the forces that created it, the more it can expand and be what it is. Kind of like Schopenhauer, Kierkegaard and Nietzsche's works. The force of their works was not felt until their works were distanced from them as the creators. While Schopenhauer, Nietzsche and Kierkegaard were alive, the distance between them and their works was too close. A storm cannot be effective and felt until it becomes distant from the forces that created it.

Bryan, your idea of the cold front colliding with the warm front sounds like a metaphor for sex. Opposites colliding, and then creating. I therefore think that, like Elizabeth, you are on the right track as well. You, me and EI. 3 forces that ought to maximize our potential for oneness. An orgy of intelligence.

The lower pressure before/during a storm is an unnatural low.

Ah, but why do you consider it unnatural?

PS: Elizabeth! Thank you for participating in my thread! hope to see you out on this thread again soon.

That goes for you too Bryan.

[Matt Gregory]

I look at it like this, which may not be entirely right, but I think it's basically right:

Think of a 3x3 tic-tac-toe grid drawn on the ground (a pretty big one). There's a certain amount of air over each square and say the temperature is 50 degrees over each square and the barometric pressure is the same, too.

Now let's say the air over the center square heats up to 75 degrees. The energy of the air molecules is increasing, which increases the pressure of the air, except for there's no resistance on the sides of the center square, so the air over the center square pushes out into the 8 surrounding squares and the pressure increases a little bit for all of the squares.

Now if the temperature of the center square cools back down to 50 degrees, then the pressure decreases and sucks some of the air back in towards the center, lowering the pressure of all the air.

So, if you were standing in one of the corner squares, the temperature of your air wouldn't change, but the pressure would seem to change for no reason. Well, maybe the temperature would change a little, but I guess my point is that air carries pressure changes faster than it carries temperature changes, so that's why there's a disconnect between the two.

[BMcGilly07]

No problem, Aaron. As for storms, they also come in the dead of winter, devoid of warm fronts, and likewise hurricanes spawned in the carribean swarm northward without colliding with a single cold front. The question of correlation is beyond me, it seems the temperature of the front harboring the storm doesn't effect the barometric reading, rather the gatheriing of air mass associated with storms would lessen the mass of air as it is drawn upward and into the storm, thus lessening air pressure on the earth's surface.

As for your orgies and whatnot, there's nothing wrong with being alone, and that's the best way I know to "maximize oneness."

[Aaron Mathis]

Matt Gregory!

It's nice to have you out on the field. Glad you could make it.

I look at it like this, which may not be entirely right, but I think it's basically right:

Think of a 3x3 tic-tac-toe grid drawn on the ground (a pretty big one). There's a certain amount of air over each square and say the temperature is 50 degrees over each square and the barometric pressure is the same, too.

Now let's say the air over the center square heats up to 75 degrees. The energy of the air molecules is increasing, which increases the pressure of the air

Ah, but wait a sec........why is this? Why does an increase in temperature, increase the pressure that air exerts on things like a barometer? For instance, if I have a pot of cold water on a stove, does the water weigh any more or less as it begins to heat up?

the air over the center square pushes out into the 8 surrounding squares and the pressure increases a little bit for all of the squares.

I wish I could see it....

I just can't quite picture what is really happening.

Now if the temperature of the center square cools back down to 50 degrees, then the pressure decreases and sucks some of the air back in towards the center, lowering the pressure of all the air.

So, if you were standing in one of the corner squares, the temperature of your air wouldn't change, but the pressure would seem to change for no reason.

You don't mean I would feel wind do you?

If not, I don't think I ever felt a noticable difference in air pressure before, whereas temperature I do.

I guess my point is that air carries pressure changes faster than it carries temperature changes, so that's why there's a disconnect between the two.

I think my problem is that I don't clearly see exactly what pressure is. I do, but I don't.

I can only think of pressure as a phenomenon where something active is effecting something passive.

I'm trying to understand why air varies in weight. For instance, it would make sense to say that the air is heavier and thus exerts more pressure when it is cold and humid. And thus likewise, the air would have less weight thus exert less pressure when it is hot and dry.

How does this sound? Less start with the basics and then slowly grow into more advanced concepts.