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Why Is Pressure A Scalar Quantity?

fluid mechanics

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#1 Chemister

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Posted 16 September 2020 - 02:18 PM

Pressure is a scalar quantity (has magnitude but no direction), while Force is a vector (has both magnitude and direction). So how can Pressure, which has no direction, give rise to a Force which has a direction?

 

 

 

 

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Edited by Chemister, 16 September 2020 - 02:19 PM.


#2 latexman

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Posted 16 September 2020 - 03:03 PM

Pressure is a force exerted in EVERY direction.  Expressing every direction is redundant because for every line of force from the origin of the pressure in the bulk solid/liquid/gas (not at a boundary) there is exactly one opposite and counter-balancing line of force 180o from it.  So, its a scalar.  Our usual interest of pressure is how does that force that is distributed on an AREA of interest add up.  That resultant force IS a vector!



#3 Chemister

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Posted 16 September 2020 - 04:13 PM

Pressure is a force exerted in EVERY direction.  Expressing every direction is redundant because for every line of force from the origin of the pressure in the bulk solid/liquid/gas (not at a boundary) there is exactly one opposite and counter-balancing line of force 180o from it.  So, its a scalar.  Our usual interest of pressure is how does that force that is distributed on an AREA of interest add up.  That resultant force IS a vector!

But from the notes I am studying from, pressure defined as the force normal to the area considered. For a fluid at rest, molecules collisions produces forces in all directions but since the fluid is not moving, hence the sum of all the forces add up to zero. I don't still get how the resultant of forces resulting from molecular collisions acting on an area of interest translate into pressure being a scalar quantity.

 

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Edited by Chemister, 16 September 2020 - 04:17 PM.





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