What is the formula for finding pressure and what is the SI unit used?    

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ishpiro eNotes educator| Certified Educator

The pressure, by definition, is the amount of force per unit area. So the formula for pressure is

`p = F/A` , where F is the magnitude of the force and A is the area of the surface to which the force is applied. Note that while the force is a vector quantity (that is, it has a direction), the pressure is a scalar quantity. The force is assumed to be acting perpencicular to the surface.

The SI unit for measuring pressure is Pascal. Using the formula above, we can express 1 Pascal in the fundamental SI units:

`[p] = ([F])/([A]) = N/m^2`

Newton, the unit of measurement of force, is `N = (kg*m^2)/s^2`

Combining these, we see that 1 Pascal equals `(kg)/s^2` .

The pressure in liquids is usually calculated using a different formula, which is

`p = rho*g*h` , where `rho` is the density of the liquid, g is the gravity acceleration and h is the depth at which the pressure is being determined. One can see by considering the units of measurement of density, acceleration and length that the unit for pressure still comes out to equal 1 Pascal, or kg/s^2.




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