What is the pressure difference?

In summary, the conversation discusses the concept of gas pressure and which gas would have a higher pressure in a static system. The speaker provides a formula to support their answer, but the teacher has given a different answer without explanation. The group suggests openly discussing with the teacher, but the speaker believes it may be better to privately give their work to the teacher. Another member suggests challenging the teacher in class to expose the misunderstanding.
  • #1
Tomy World
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Thread moved from the technical forums to the schoolwork forums
TL;DR Summary: Which gas has a higher pressure and why? School has provided answer which I disagree. Like to hear comment from others.

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  • #2
Welcome to PF.

If the system is static, then gas A has the higher pressure as it pushes the mercury towards the other gas B.
What do you think?
 
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  • #3
Baluncore said:
Welcome to PF.

If the system is static, then gas A has the higher pressure as it pushes the mercury towards the other gas B.
What do you think?
Yah. It's quite straight forward, right?

My answer is
PA + ρgH1 = PB + ρgH2
PA = PB + ρg(H2-H1)

Since H2>H1, therefore PA > PB.

But teacher wrote the other way round, saying that PB is higher without given more explanation. And students hesitate to challenge teacher... I'd encourage them to openly discuss with teacher ;)
 
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  • #4
Tomy World said:
And students hesitate to challenge teacher... I'd encourage them to openly discuss with teacher ;)
When you think a teacher gets it wrong, if you want good marks, do NOT challenge the teacher in front of the class. Give a copy of your work to the teacher after the class. Either you or the teacher will be wrong, neither of you needs public embarrassment or loss of face.
 
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  • #5
Baluncore said:
When you think a teacher gets it wrong, if you want good marks, do NOT challenge the teacher in front of the class. Give a copy of your work to the teacher after the class. Either you or the teacher will be wrong, neither of you needs public embarrassment or loss of face.
May be 'challenge' is a strong word. I don't mean that ;)
 
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  • #6
Your teacher should be ashamed. Ask if the teacher is sure of the result?
 
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  • #7
With an error this egregious and a resolution that is relatively straightforward to work out, my inclination would be to challenge the teacher in class. The misunderstanding needs to be exposed, rather than swept under the carpet.

The one time I had a similar disagreement (I was correct, TA was in error), I wound up being disagreed with by the TA and berated by the rest of the class. I shut up so that we could get on with the rest of the subject matter. No big deal. I knew I was right. I knew the TA was wrong and I had a good idea why. I didn't need the grade or the peer approval. I was in school to learn, not to obtain a credential or to garner the respect of others.

At the beginning of our next session, the TA had the good grace to apologize in front of the class and provide the explanation of error that I had anticipated.
 
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  • #8
jbriggs444 said:
With an error this egregious and a resolution that is relatively straightforward to work out, my inclination would be to challenge the teacher in class.
I agree. Any teacher who is offended by a POLITE challenge doesn't belong there.
 
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FAQ: What is the pressure difference?

What is the pressure difference?

The pressure difference, also known as pressure gradient, is the difference in pressure between two points in a fluid or gas. It drives the flow of the fluid from the region of higher pressure to the region of lower pressure.

How is pressure difference measured?

Pressure difference is typically measured using devices such as manometers, differential pressure sensors, or pressure gauges. These instruments measure the difference in pressure between two points and provide a reading in units such as Pascals (Pa), pounds per square inch (psi), or millimeters of mercury (mmHg).

Why is pressure difference important?

Pressure difference is crucial in various applications, including fluid dynamics, meteorology, and engineering. It influences the movement of fluids in pipelines, the behavior of weather systems, and the operation of equipment like pumps and compressors.

What factors affect the pressure difference?

Several factors can affect the pressure difference, including the density of the fluid, the height difference between the two points, the temperature, and the presence of any obstacles or restrictions in the flow path. Changes in any of these factors can alter the pressure gradient.

How does pressure difference relate to flow rate?

The pressure difference is directly related to the flow rate in a fluid system. According to Bernoulli's principle and the Hagen-Poiseuille equation, a greater pressure difference generally results in a higher flow rate, assuming the fluid's viscosity and the dimensions of the flow path remain constant.

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