This topic summary covers Knowledge Organiser: Density within Density for GCSE Physics. Revise Density in Particle Model for GCSE Physics with 13 exam-style questions and 30 flashcards. This is a high-frequency topic, so it is worth revising until the explanation feels precise and repeatable. It is section 14 of 14 in this topic. Use this topic summary to connect the idea to the wider topic before moving on to questions and flashcards.
Topic position
Section 14 of 14
Practice
13 questions
Recall
30 flashcards
Knowledge Organiser: Density
Key Terms
- Density (ρ): mass per unit volume
- Displacement: volume of fluid pushed aside by an object
- Upthrust: upward force on a submerged object
- Regular solid: shape with calculable volume (cube, cylinder)
- Irregular solid: shape needing displacement method
Key Facts
- Density is a property of the material, not the object size
- Water density = 1000 kg/m³ = 1 g/cm³ (benchmark)
- Objects float if density < fluid density
- Objects sink if density > fluid density
- Gases are ~1000× less dense than solids/liquids
Key Equations
- ρ = m / V (density = mass ÷ volume)
- Units: kg/m³ or g/cm³
- Conversion: 1 g/cm³ = 1000 kg/m³
- Displacement volume: V = V₂ − V₁
- Higher: P = ρgh (fluid pressure)
Exam Tips
- Always show units in density calculations
- For displacement: volume = final − initial reading
- Air bubbles on object = source of error in practical
- Cutting a material in half does NOT change its density
Common Mistakes
- Confusing mass and density: A larger object is not necessarily denser — density depends on mass per unit volume, not total mass
- Wrong units in calculations: If mass is in g and volume in cm³, density is in g/cm³ — convert to kg and m³ if SI units are required
- Not subtracting initial volume in displacement: When using a measuring cylinder, volume of object = final reading − initial reading — do not use the final reading alone
- Saying density changes when you cut a material: Density is an intrinsic property — cutting a block in half halves both mass and volume, so density stays the same
- Air bubbles in the displacement practical: Air bubbles on the object's surface add extra apparent volume — this is a source of error that makes density appear too low
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Practice Questions for Density
What is the correct equation for density?
Explain why gases have a much lower density than solids, using ideas about particles.
Quick Recall Flashcards
13 questions on Density — practise free
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