5.6 know and use the relationship for pressure difference

pressure difference = height x density x gravitational constant


p = h x ρ x g

NOTE: You may have learnt the gravitational constant on earth to be approximately 9.8 (as did I) BUT it is rounded to 10 for iGCSE exams (it's on the formula sheet) so make sure to use 10 in exams not 9.8

For example...

The density of water is 1g/cm³. Find the pressure difference between the top and bottom of a 3m vertical column of water.

First, convert all units into the same (sorry, that didn't make much sense). Basically what im saying os ensure all measurements are in the same unit, like all distance is in m (or cm) and all mass is in kg (or g) etc. In this particular example, we need to convert 1g/cm³ into kg/m³ (alternatively, you could convert the 3m into cm, but for now lets stick with kg/m³). So...

1g/cm³ = 1000kg/cm³ and in this example we only have 1g/cm³ so no calculations regarding units have to take place :)

Next substitute all the facts we are given into the equation 'pressure difference = height x ρ x g

Pressure difference = 3 x 1000 x 10 = 30,000 Pa

NOTE: Pa (pascals) is equivalent to N/m² so don't be thrown of in an exam situation if the unit given is N/m² (it basically means pascals, the unit for pressure)

example credit: CGP