5.3 describe experiments to determine density using direct measurements of mass and volume

1. First, measure the mass of an object (weigh it)
2. Then measure the volume. If the object is irregular (e.g. not a cuboid/easily measurable-shape*, then take a set amount of water (eg. 100ml) and fully submerge the object in the water. Measure the rise of the water (eg. From 100ml to 130ml). Or measure using a eureka can. If object is regular, however, you can measure lengths to find the volume.
3. Use the equation density = mass/volume to find the density

*okay so easily-measurable shape isn't correct English but you get what I mean

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

5.4 know and use the relationship between pressure, force and area:

pressure = force / area

p = F / A

NOTE: do not get confused with p (pressure) and  ρ (rowe, density)

5.5 understand that the pressure at a point in a gas or liquid which is at rest acts equally in all directions

Pressure is a measure of the force being applied to the surface of something. In gases and liquids (at rest) the pressure at any point acts equally in all directions. for example, if you fill a bag with water, then poke a hole at the bottom of the bag, water will 'squirt' out of the bag (obviously). However, if you put a hole near the top of the bag, the water will 'squirt' out with the same force. This is because the pressure of the water is the same at the top of the bag as it is in the  bottom of the bag.

5.2 know and use the relationship between density, mass and volume:

density = mass / volume

ρ = m / v


NOTE: do not get confused with p (pressure) and  ρ (rowe, density)