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Density is ρ = m/V. Choose consistent units such as kg m⁻³ or g cm⁻³. Measure a regular solid’s dimensions to calculate volume; use displacement for a suitable irregular solid. For a liquid, subtract container mass and measure volume. An air bubble attached to a submerged object can make the displacement too large and the calculated density too low. Explain the direction of an error using the equation.
Video by Cognito. The video’s own board label is retained; follow the specification reference and scope notes on this lesson for assessed content.
Viewing focus: Calculate density
After watching, attempt these questions before opening the answers. You can also use the written lesson below.
After watching 1: What is density?
Mass divided by volume. State the unit system used.
After watching 2: Why can temperature stay constant while melting?
Energy changes particle arrangements. Potential energy changes during the transition.
What you'll be able to do
Density is ρ = m/V. Choose consistent units such as kg m⁻³ or g cm⁻³. Measure a regular solid’s dimensions to calculate volume; use displacement for a suitable irregular solid. For a liquid, subtract container mass and measure volume. An air bubble attached to a submerged object can make the displacement too large and the calculated density too low. Explain the direction of an error using the equation.
Internal energy is the total kinetic and potential energy of particles in a system. Temperature relates to average particle kinetic energy. Heating can increase particle speeds or change particle arrangements during a state change. A larger sample at the same temperature can have more internal energy. Particles in a solid vibrate; liquid particles can move around one another; gas particles are far apart and move randomly.
During melting or boiling of a pure substance at fixed pressure, supplied energy changes particle arrangements and their potential energy while temperature remains approximately constant. Specific latent heat links energy, mass and state change through E = mL. Distinguish fusion from vaporisation and use the value supplied. Melting and boiling preserve particle identity, while a chemical reaction changes the substances. Evaporation can occur at a surface below boiling temperature.
Attempt these problems on paper before opening the worked reasoning. Explain your steps as well as giving a final answer.
Common mistakes to avoid
Key takeaways
Question 1: Melt 0.50 kg ice using latent heat 334000 J kg⁻¹ at its melting temperature. Find energy.
167000 J, without a temperature rise during melting.
Check the assessed scope and practical or mathematical requirements.
An external explanation or interactive activity to use alongside the lesson. It may include extension material.
Close the notes and answer from memory. Revisit any explanation you cannot yet reconstruct.
Test yourself
Answer a few questions, then review anything you missed.
Start with the quiz above to check the key ideas. You can also choose another topic from the practice library.