Question

how is SI unit of pressure derived

Answer 1

Pressure=Force\area
S.I. unit of Force is N.
S.I. unit of area is m².
As it is Force\area,
S.I. unit of pressure =N/m².

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Hope this will help you.

Answer 2

SI unit of pressure is PASCAL=N/m² = force/area
force = Newton(N)
area = m²