Density is perhaps the most-used concept in physics that doesn't have a specific location in the Subject Guide. It can be used in gases, standing waves, gravitation, fuels, heat transfer, fluids (AHL Engineering) and cosmology (AHL Astrophysics).
Key Concepts
Density is defined as the ratio of the mass of a body to its volume:
\(\rho={m\over V}\)
- \(\rho\) is density in kg m-3
- \(m\) is mass in kg
- \(V\) is volume in m3
The density of a gas is lower than the density of a solid. But not all liquids are less dense than solid bodies. On a macroscopic level, densities cause bodies to float or sink. On a microscopic level, density is related to the spacing of particles.
Because density is unrelated to the dimensions of a body, it is a material property. A given material will always have the same density, irrespective of whether it is a gigantic sphere or stretched out into a sheet.
Informally, some refer to density as 'the amount of stuff in a thing'.
After revising the full SL course, can you spot the links between density and these five concepts?
- Gases
- Standing waves
- Gravitation
- Fuels
- Heat transfer
How much of Density have you understood?
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