IBPhysicsHLRevision NotesThe Particulate Nature of MatterThermal Energy TransfersDensity

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First teaching 2023

First exams 2025

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Density (HL IB Physics)

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Density

  • Density is the mass per unit volume of an object
    • If two objects occupy the same volume, the object with a lower density will have a lower mass
    • For example, a bucket filled with feathers will have a lower mass than the same bucket filled with sand, because feathers have a lower density than sand

  • The units of density depend on the units used for mass and volume:
    • If the mass is measured in g and volume in cm3, then the density will be in g / cm3
    • If the mass is measured in kg and volume in m3, then the density will be in kg / m3

How to calculate density

How to Calculate Density, for IB Physics Revision Notes

Comparison of Molecular Densities, for IB Physics Revision Notes

Gases are less dense than liquids due to their molecular arrangements

  • The volume of an object may not always be given directly but can be calculated using the appropriate formula

Volumes of common 3D shapes

How to Calculate Volume of Regular Shapes, for IB Physics Revisios Notes

Worked example

A paving slab has a mass of 73 kg and dimensions 40 mm × 500 mm × 850 mm.

Calculate the density, in kg m-3 of the material from which the paving slab is made.

Density of a Slab Worked Example, for IB Physics Revisios Notes

Answer:

WE - Density answer image, downloadable AS & A Level Physics revision notes

Examiner Tip

When converting a larger unit to a smaller one, you multiply (×)

  • E.g. 125 m = 125 × 100 = 12 500 cm

When you convert a smaller unit to a larger one, you divide (÷)

  • E.g. 5 g = 5 / 1000 = 0.005 or 5 × 10-3 kg

When dealing with squared or cubic conversions, cube or square the conversion factor too

  • E.g. 1 space mm cubed space equals 1 over 1000 cubed space equals space 1 cross times 10 to the power of negative 9 end exponent space straight m cubed
  • E.g. 1 space cm cubed space equals space 1 over 100 cubed space equals space 1 cross times 10 to the power of negative 6 end exponent space straight m cubed

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    Katie M

    Author: Katie M

    Expertise: Physics

    Katie has always been passionate about the sciences, and completed a degree in Astrophysics at Sheffield University. She decided that she wanted to inspire other young people, so moved to Bristol to complete a PGCE in Secondary Science. She particularly loves creating fun and absorbing materials to help students achieve their exam potential.