Density (Edexcel GCSE Physics) : Revision Note

Ashika

Author

Ashika

Last updated

Did this video help you?

Density

  • Density is defined as:

    The mass per unit volume of a material

  • Objects made from low density materials typically have a low mass

  • Similarly sized objects made from high density materials have a high mass

    • For example, a bag full of feathers is far lighter compared to a similar bag full of metal

    • Or another example, a balloon is less dense than a small bar of lead despite occupying a larger volume

  • Density is related to mass and volume by the following equation:

Density equation, downloadable AS & A Level Physics revision notes
  • Gases, for examples, are less dense than solids because the molecules are more spread out (same mass, over a larger volume)

Density comparison, downloadable AS & A Level Physics revision notes

Gases are less dense than solids

  • This equation can be rearranged with the help of the formula triangle:

Density triangle (2), IGCSE & GCSE Physics revision notes

Density, mass, volume formula triangle

  • The units of density depend on what units are 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

  • This table gives some examples of densities on common materials

    • If a material is more dense than water (1000 kg/m3), then it will sink

Approximate Densities of Materials Table

Table of densities of common materials, downloadable IGCSE & GCSE Physics revision notes
  • The volume of an object may not always be given directly, but can be calculated with the appropriate equation depending on the object’s shape

Volume of shapes, downloadable AS & A Level Physics revision notes

Volumes of common 3D shapes

Worked Example

A paving slab has a mass of 73 kg and dimensions 0.04 m × 0.5 m × 0.85 m.

Worked Example Density, downloadable IGCSE & GCSE Physics revision notes

Calculate the density, in kg/m3, of the material from which the paving slab is made.

Answer:

Step 1: List the known quantities

  • Mass of slab, m = 73 kg

  • Volume of slab, V = 0.04 m × 0.5 m × 0.85 m = 0.017 m3

Step 2: Write out the equation for density

Step 3: Substitute in values

ρ = 73 ÷ 0.017 = 4294 kg/m3

Step 4: Round the answer to two significant figures

ρ = 4300 kg/m3

Examiner Tips and Tricks

Make sure you are comfortable converting between units such as metres (m) and centimetres (cm) or grams (g) and kilograms (kg).

  • 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

👀 You've read 1 of your 5 free revision notes this week
An illustration of students holding their exam resultsUnlock more revision notes. It's free!

By signing up you agree to our Terms and Privacy Policy.

Already have an account? Log in

Did this page help you?

Ashika

Author: Ashika

Expertise: Physics Content Creator

Ashika graduated with a first-class Physics degree from Manchester University and, having worked as a software engineer, focused on Physics education, creating engaging content to help students across all levels. Now an experienced GCSE and A Level Physics and Maths tutor, Ashika helps to grow and improve our Physics resources.

Download notes on Density