Slides
Lesson slides
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Open resourceLesson 07
Pressure and Density
Define density and pressure, measure density experimentally, and use both ideas in simple mechanics problems.
Objectives
Lesson outcomes
- Define density and pressure and use the equations rho = m / V and p = F / A.
- Describe how to determine the density of a liquid, a regular solid, and an irregular solid by displacement.
- Explain how pressure changes with force and area in everyday situations.
- Solve straightforward density and pressure calculations with correct units.
Syllabus
CIE 0625 syllabus points
4 linked
- 1.4.1 Define density as mass per unit volume; recall and use the equation m ρ = V
- 1.4.2 Describe how to determine the density of a liquid, of a regularly shaped solid and of an irregularly shaped solid which sinks in a liquid (volume by displacement), including appropriate calculations
- 1.8.1 Define pressure as force per unit area; recall and use the equation F p = A
- 1.8.2 Describe how pressure varies with force and area in the context of everyday examples
Definitions
Required definitions
Density
mass per unit volume.
Pressure
force per unit area.
Lesson Notes
Student guidance and lesson notes
Overview
Keep the distinction between force, area, pressure, mass, volume, and density explicit.
What You Need to Know
- Connect density to the idea of how closely packed matter is.
- Model the density methods for liquids, regular solids, and irregular solids that sink, including displacement for volume.
- Use everyday examples such as sharp blades, snowshoes, and tyres to make the pressure relationships concrete.
- Keep the two equations separate in you’ minds by constantly naming the quantities and units.
- Try one or two simple worked calculations that contrast density and pressure so the formulas do not blur together.
How to Work Through It
- Start with a retrieval prompt on mass, volume, and force.
- Work through density and its practical measurements, including displacement for irregular solids.
- Introduce pressure through force-and-area examples and practise the pressure equation.
- Finish with mixed questions that require you to choose the correct model and equation.
Check Your Understanding
- Check whether you can choose whether a situation is best explained by density or pressure and justify the choice.
- Try one hinge question where you identify how to measure the volume of an irregular solid.
- Try one density and one pressure calculation to check that the equations are not being confused.
Common Mistakes
- Swapping the density and pressure equations because both are ratios. Keep the quantities and units visible in every example.
- Some think a larger force always means a larger pressure. Revisit the role of area.
- Displacement methods can go wrong if you do not read the initial and final volume carefully.
Next Steps
- Use the calculation and past-paper resources for additional equation practice.
- Carry forward density and liquid ideas into floating, sinking, and liquid pressure.
Lesson Resources
Materials for this lesson
Use these videos, slide decks, documents, or links to work through the lesson.
Document
Pressure calculations
Practice textbook style questions
Open resourceDocument
Past paper questions
Practice past exam questions
Open resource