# Solving an Air Pressure Question: Who Is Right?

• Callmelucky
In summary, the conversation discusses the concept of air pressure inside a test tube that is pushed into water. The pressure is determined by the hydrostatic pressure, which is the product of the density of water, the change in height, and the gravitational constant. The conversation also clarifies the meaning of "epruvete" (or test tube) and discusses the role of air and water in determining the pressure inside the tube.
Callmelucky
Homework Statement
I might be wrong but I think it is author.
Relevant Equations
Pressure= density * g * h
Can someone please answer this question, so I can figure who is wrong here, me or author. Thank you.1.question (picture below): empty epruvete turned upside down is dipped in glass filled with water to the depth H. While doing that water enters the epruvete and reaches height of h. The AIR pressure inside the epruvete is: I wrote just density(of air) * g(gr. const.)* height(of epruvete - h). The answer is apparently Po(air pressure) + density * g(gr. const.) * (H-h). I am not sure if it's ment density of water or air(since it's not stated), but if they mean density of water I don't understand how is that so, I don't get what water has to do with air pressure inside the epruvete(if pressure = F/A), so please explain if you can/want. Thank you.

But anyway I think that air pressure inside the epruvete should be density(of air) * g(gr. const.) * height(of epruvete - h), if hidrostatic pressure= density * g * height.

Thank you.

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1. A mercury barometer is a pipe with a closed top that is long enough to have a vacuum above the mercury.

So yes, there is sufficient Hg to fill a column.

2. I have no idea what an epruvete is (google come up with that ?). But from the picture I expect the pipe is not empty at all, but filled with air. There is no Hg here, so they mean the density of water. The pressure at the water level in the pipe is ambient pressure plus some ##\rho g \,\Delta h## :

which I hope you understand by now... ?
( height(of epruvete - h) ... ?)

##\ ##

erobz and Callmelucky
BvU said:
1. A mercury barometer is a pipe with a closed top that is long enough to have a vacuum above the mercury.

So yes, there is sufficient Hg to fill a column.

2. I have no idea what an epruvete is (google come up with that ?). But from the picture I expect the pipe is not empty at all, but filled with air. There is no Hg here, so they mean the density of water. The pressure at the water level in the pipe is ambient pressure plus some ##\rho g \,\delta h## :
View attachment 321768

which I hope you understand by now... ?
( height(of epruvete - h) ... ?)

##\ ##
epruvete is test tube, I thought that is the same on all languages(my bad).

Yeah but, in task it's asked for air pressure inside test tube.

It's not a barometer.

BvU
Edit: Sorry. I didn't read BvU properly. I think he already said this.

Eprouvette is just a test tube. Eprouver = to test (from french)
Presumably filled with air. As pushed into water, air is compressed and stops water rising to outside level.

Level depression is delta h, so internal pressure is just (density of water) x (delta h) x (g) above atmospheric.
IE. just the hydrostatic pressure, because the pressure of the water at the water/air interface in the tube must be that. What's inside the tube is irrelevant.

BvU and Callmelucky
BvU said:
1. A mercury barometer is a pipe with a closed top that is long enough to have a vacuum above the mercury.

So yes, there is sufficient Hg to fill a column.

2. I have no idea what an epruvete is (google come up with that ?). But from the picture I expect the pipe is not empty at all, but filled with air. There is no Hg here, so they mean the density of water. The pressure at the water level in the pipe is ambient pressure plus some ##\rho g \,\Delta h## :
View attachment 321768

which I hope you understand by now... ?
( height(of epruvete - h) ... ?)

##\ ##
I didn't understand at first, now I do. Thank you for taking time to answer both of my questions.

Lnewqban and BvU
Merlin3189 said:
Edit: Sorry. I didn't read BvU properly. I think he already said this.

Eprouvette is just a test tube. Eprouver = to test (from french)
Presumably filled with air. As pushed into water, air is compressed and stops water rising to outside level.

Level depression is delta h, so internal pressure is just (density of water) x (delta h) x (g) above atmospheric.
IE. just the hydrostatic pressure, because the pressure of the water at the water/air interface in the tube must be that. What's inside the tube is irrelevant.
thank you for clarifying,

Lnewqban

## What is air pressure and how is it measured?

Air pressure is the force exerted by the weight of air in the atmosphere on a surface. It is typically measured using a barometer, with units of measurement including Pascals (Pa), atmospheres (atm), or inches of mercury (inHg).

## How does altitude affect air pressure?

As altitude increases, air pressure decreases. This is because there is less air above a given point at higher altitudes, resulting in lower weight and, consequently, lower pressure.

## What factors can cause variations in air pressure at the same altitude?

Variations in air pressure at the same altitude can be caused by temperature changes, humidity levels, and weather systems. Warmer air tends to have lower pressure, while cooler air has higher pressure. Additionally, high and low-pressure systems can move through an area, causing fluctuations.

## How can I determine who is right in an air pressure debate?

To determine who is right in an air pressure debate, you need to consider the specific conditions and factors being discussed, such as altitude, temperature, and weather patterns. Using accurate measurements and scientific principles, you can compare the claims to see which aligns with established understanding.

## What are some common misconceptions about air pressure?

Common misconceptions about air pressure include the belief that air pressure is the same everywhere at the same altitude, that it doesn't change with weather, and that it only affects the weather. In reality, air pressure varies with temperature, humidity, and weather systems, and it influences various phenomena, including flight and breathing.

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