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A Question About Weight and Pressure

  • Thread starter MBrain
  • Start date
  • #1
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Hello there :) First I'm sorry for my English it might be kinda bad !

I Have a little question about Weight and Pressure, Hope this is the right place.

1qh501.jpg


Here in this image we have 3 samples, A, B and C.

They are 3 different types of shapes fulled with a liquid (let's say water)

Talking about the physical pressure on the bottom of every shape :-

In Sample (A) we can see that Weight = Pressure.
In Sample (B) we can see that Weight < Pressure.
In Sample (C) we can see that Weight > Pressure.

Where did we get the extra pressure in the sample (B) ? It's like we create that green area from nowhere!
And where did the extra weight go in the sample (C) ? It's like we lost that orange area and it's nothing!

Hope I can fine the answer, Thank you :) !
 

Answers and Replies

  • #2
Doc Al
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In Sample (A) we can see that Weight = Pressure.
In Sample (B) we can see that Weight < Pressure.
In Sample (C) we can see that Weight > Pressure.
Where you say "weight", I assume you mean "weight/area". (Which would give you a pressure term.)
Where did we get the extra pressure in the sample (B) ? It's like we create that green area from nowhere.
The slanted walls exert a downward force.
And where did the extra weight go in the sample (C) ? It's like we lost that orange area, or it is nothing!
Here the slanted walls exert an upward force.
 
  • #3
Delphi51
Homework Helper
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Weight and pressure are very different things. For starters, weight is a force and has units of Newtons. Pressure is a force per unit area and has units of N/m². Weight only acts downward toward the center of the Earth. Pressure acts in all directions simultaneously.

Pressure is not like light intensity (energy/m²), either. If you increase the area on the bottom, the pressure at the bottom is spread over a larger area but it is not thereby diminished as light intensity would be if spread over a larger area. Consider a balloon. If you blow it up to a pressure of 1.1 atmospheres, then pump it up to 1.2 the balloon gets larger and the pressure is 1.2 on every bit of the larger surface area.
 
  • #4
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Where you say "weight", I assume you mean "weight/area". (Which would give you a pressure term.)

The slanted walls exert a downward force.

Here the slanted walls exert an upward force.
And where that forces come from ?!
 
  • #5
Doc Al
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And where that forces come from ?!
The pressure of the water against the containing walls. Which, as pointed out by Delphi51, acts the same in all directions.
 
  • #6
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Doc Al and Delphi51 Thank you for your helping.
but when I explained it that way to my teacher he said that its not exactly the right answer.
I think he is looking for a really advance answer that explains it all.
 

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