Difference between revisions of "Pressure"

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(Created page with '==Definition== '''Pressure''' between two surfaces in contact is the defining ingredient::normal force per unit area between them. More precisely, the pressure at a point on…')
 
(Units and dimensions)
 
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==Units and dimensions==
 
==Units and dimensions==
  
The MLT dimensions of pressure are <math>ML^{-1}T^{-2}</math>. The SI units of pressure are <math>N/m^2</math> (Newton per meter squared) or <math>kgm^{-1}s^{2}</math>, which is also called <math>Pa</math> (Pascal).
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{| class="sortable" border="1"
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! Question !! Answer
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|-
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| Scalar or vector? || [[Quantity type::Scalar]]
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|-
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| Instantaneous or time-cumulative? || [[Quantity type::Instantaneous]]
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|-
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| MLT dimensions || <math>ML^{-1}T^{-2}</math>: [[MLT::MLT;1;-1;-2]]
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|-
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| SI units || <math>Pa</math> (Pascal) or <math>N/m^2</math> (Newton per meter squared)
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|-
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| Other units || <math>Atm</math> (atmospheric pressure)
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|}

Latest revision as of 01:17, 21 January 2010

Definition

Pressure between two surfaces in contact is the normal force per unit area between them. More precisely, the pressure at a point on the surface of contact is the differential of the normal force with respect to area at the point.

In symbols:

P = \frac{dN}{dA} = \frac{\partial^2 N}{\partial x \partial y}

Equivalently, the pressure at a point on the surface of contact is the limit of the force per unit area of smaller and smaller regions in the surface of contact containing the point.

When the normal force is uniformly distributed over the surface of contact, the pressure is given by the formula:

P = \frac{N}{A}

Pressure is treated as a scalar, i.e., it is not given a direction, even though normal force is treated as a vector. The vector analogue of pressure is stress.

Units and dimensions

Question Answer
Scalar or vector? Scalar
Instantaneous or time-cumulative? Instantaneous
MLT dimensions ML^{-1}T^{-2}: MLT;1;-1;-2
SI units Pa (Pascal) or N/m^2 (Newton per meter squared)
Other units Atm (atmospheric pressure)