Density and Pressure

Density

Density is a measure of how compact the mass in a substance or object is. It is calculated by dividing the mass of the substance by its volume.
The formula for density is density = mass/volume.
The SI unit of density is kilograms per cubic metre (kg/m³), but it can also be measured in grams per cubic centimetre (g/cm³) where 1 g/cm³ = 1000 kg/m³.
More dense substances have particles that are more closely packed together.
In the context of solids, liquids, and gases, solids generally have a higher density because their particles are closely packed together.
Comparatively, gases usually have the lowest density as their particles are spread out.
Heating a substance can also cause it to expand, which increases its volume and therefore reduces its density.
Understanding density is essential for predicting whether an object will float or sink when placed in a fluid.

Pressure

Pressure is the amount of force exerted per unit area.
The formula for pressure is pressure = force/area.
The SI unit of pressure is pascal (Pa), but it can also be measured in atmospheres (atm), and millimetres of mercury (mmHg).
Pressure is experienced differently across solids, liquids, and gases.
Solid materials distribute applied pressure evenly across their entire surface, while liquids and gases apply pressure equally in every direction.
An increase in temperature of a gas will increase its pressure, if the volume is kept constant. This is known as Gay-Lussac’s law.
A decrease in the volume of a gas will increase its pressure, if the temperature is kept constant, known as Boyle’s law.
Atmospheric pressure decreases with height.

Remember, concepts of density and pressure are integral for understanding behaviours of solids, liquids, and gases and state changes between these.