Pascal (Pa)

Also called Pa, N/m^2

The pascal is the SI unit of pressure, equal to one newton spread over one square metre. It is a very small amount of pressure: atmospheric pressure at sea level is about 1.0 times 10 to the fifth pascals.

One newton spread over one square metre:

1 Pa=1 N/m21\ \text{Pa} = 1\ \text{N/m}^2

That is the unit attached to P=F⊥/AP = F_{\perp}/A wherever the AP sheets print it.

A pascal is tiny. A sheet of 80 gram-per-square-metre paper lying flat presses down at about 0.80.8 Pa, whatever size the sheet is, because weight and area scale together. The AP tables of information put one atmosphere at 1.0×105 N/m2=1.0×105 Pa1.0 \times 10^5\ \text{N/m}^2 = 1.0 \times 10^5\ \text{Pa}, so the air is already pushing a hundred thousand times harder than that. Real answers land in kilopascals, and a fluid result of a few pascals usually means a prefix went unconverted.

The scale also explains the gap between the two pressures a question can ask for. Absolute and gauge pressure differ by exactly the atmospheric term, 1.0×1051.0 \times 10^5 Pa, which swamps most gauge readings. Going down through water adds ρgh=(1000)(9.8)(1)=9800\rho g h = (1000)(9.8)(1) = 9800 Pa per metre of depth, so ten metres of water roughly doubles the absolute pressure you started with at the surface.

Which sheets print it. Pascal is in the unit-symbol table of two of the four AP tables of information, AP Physics 1 and AP Physics 2. The AP Physics C: Mechanics table lists seven unit symbols and the C: Electricity and Magnetism table lists fifteen, and neither list includes it, because neither course covers fluids or thermodynamics.

Capitalise Pascal only when you mean the man. The unit is a pascal and the symbol is Pa.

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