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Regular and Irregular Objects

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GCSE Physics Density Practical: Regular and Irregular Objects

An enhanced GCSE Physics practical guide to determining the density of regular and irregular solids using mass, dimensions and water displacement, with particle-model links, worked calculations, graph skills, uncertainty, troubleshooting, extensions, technician preparation and exam support.

GCSE Physics student measuring the density of regular and irregular objects

Teacher note: This resource is provided as a practical support guide to accompany laboratory equipment. Teachers should adapt procedures and risk assessments to suit their curriculum requirements, examination board specifications and local laboratory policies.

Level
GCSE Physics
Core lesson time
Approx. 60 minutes
Risk level
Low
Core skills
Mass, volume and density
Extensions
Liquids, graphs and sinkers
01
Practical overview 02
Background theory 03
Apparatus 04
Method and variables 05
Results and calculations 06
Processing and graphs 07
Troubleshooting 08
Errors and evaluation 09
Extensions 10
Risk assessment 11
Teacher and technician notes 12
Exam support and plenary

Practical overview

In the core investigation, students determine the density of a regularly shaped solid from its dimensions and mass, then determine the density of an irregular solid using water displacement. A carousel arrangement works well because it lets groups practise both volume methods. An optional extension determines the density of a liquid and uses a mass-volume graph.

Why this practical matters

Density is central to material selection, construction, ship and aircraft design, geology, recycling and medicine. Students turn the particle model into measurable evidence by selecting suitable instruments, combining measurements into a derived quantity, converting units and comparing results with reference data. The regular and irregular routes also make uncertainty visible because a small error in a dimension or displaced volume can noticeably change the calculated density.

Core enquiry questions

  • How can mass and volume measurements be used to determine the density of regular and irregular objects?
  • Can the measured density be used to identify the material?

Learning objectives

  • Select a balance and suitable length or volume apparatus.
  • Measure mass, length, diameter, height and displaced volume accurately.
  • Calculate the volume of cuboids and cylinders.
  • Use a measuring cylinder or displacement can for irregular objects.
  • Calculate density using ρ = m / V and include correct units.
  • Convert between g/cm3 and kg/m3.
  • Compare measured density with reference values without overclaiming.
  • Evaluate reliability, validity, accuracy and uncertainty.

Suggested teaching sequence

Teach the regular-object route first so students practise mass, dimensions and volume formulae. Follow with water displacement, emphasising eye-level meniscus readings, full submersion and the difference between initial and final volume. Use the liquid-density or mass-volume graph extension after students understand density as mass per unit volume.

Scientific background

Density describes how much mass is contained in a given volume. It is a property of a material, not simply a measure of how heavy or how large an object is.

Density equation

ρ = m / V

ρ = density
m = mass
V = volume

Common units

kg/m3 is the SI unit.
g/cm3 is commonly used for laboratory solids.

1 g/cm3 = 1000 kg/m3
1 cm3 = 1 mL

Key distinction

Density is not the same as mass or weight. A large piece of a low-density material can have more mass than a small piece of a high-density material.

Volume method What is measured Calculation
Regular cuboid Length, width and height V = l × w × h
Regular cylinder Diameter or radius, and height V = πr2h
Irregular solid Water displaced V = final volume - initial volume, or collected overflow

Particle-model interpretation

Observation Particle-model explanation
A larger sample of the same material has more mass. It contains more particles and occupies more volume in the same proportion, so density stays approximately constant.
Equal volumes of different materials can have different masses. Particle mass and particle arrangement both affect mass per unit volume.
Most solids are denser than gases. Their particles are much closer together, so more mass is present in each unit volume.
An object may float in a liquid. Its average density is lower than the liquid density, so upthrust can balance its weight before full submersion.

Bulk density: for hollow, porous or composite objects, this experiment gives an average or bulk density for the whole object. It may not equal the density of the solid material alone.

Particle model explanation of low medium and high density

Equipment required

Per student group: regular-object method

  • Digital balance, preferably reading to 0.1 g or better for small samples.
  • Millimetre ruler.
  • Vernier callipers or micrometer where appropriate.
  • Regular metal, plastic or wooden blocks and cylinders.
  • Calculator and results sheet.
  • Paper towels so objects are dry before weighing.

Per student group: irregular-object method

  • Digital balance.
  • Displacement can on a stable stand, or a measuring cylinder large enough for the object.
  • Measuring cylinders of different capacities and graduations.
  • Beaker of water and an empty catch beaker.
  • Thin string or cotton with prepared loops.
  • Irregular non-porous objects that sink and do not dissolve.
  • Tray, cloths and paper towels for spills.

Safety equipment

  • Eye protection where objects are sharp, brittle or likely to chip.
  • Closed shoes and a clear floor area when dense metal objects are used.
  • A spill tray and cloths to keep water away from electrical balances.

Teacher / technician equipment

Reference density table; labelled object sets; check masses; spare balance batteries or power leads; spare callipers; food colouring for clearer meniscus demonstrations; funnels; extra string; spare cylinders; absorbent towels; and one tested demonstration setup.

Complete density apparatus setup for regular and irregular solids

Method

1. Prepare and zero the balance
Place the balance on a level, dry bench. Check that it reads zero before each object, or use the tare function correctly.
2. Measure the mass
Dry the object thoroughly. Place it in the centre of the pan and record the mass with the balance resolution and unit.
3. Choose the volume method
Use dimensions for a regular solid. Use water displacement for an irregular solid or a shape whose dimensions cannot be measured reliably.
4. Measure a regular object
Use a ruler, Vernier callipers or micrometer as appropriate. Measure length, width and height for a cuboid, or diameter and height for a cylinder. Repeat dimensions at different positions if the object is not perfectly uniform.
5. Calculate regular-object volume
Use V = l × w × h for a cuboid or V = πr2h for a cylinder. Use radius, not diameter, in the cylinder formula and keep units consistent.
6. Prepare the displacement method
Measuring cylinder: record the initial water volume at eye level. Displacement can: fill above the spout, let excess water run out and wait until dripping stops.
7. Submerge the irregular object
Tie the object with thin string and lower it slowly until completely submerged. Remove trapped air bubbles. Do not allow water to splash out or miss the measuring cylinder.
8. Determine irregular-object volume
Cylinder: object volume = final volume - initial volume. Can: collected water volume equals object volume. Use 1 mL = 1 cm3.
9. Calculate density
Use ρ = m / V. Record the answer in g/cm3 or kg/m3 and use a sensible number of significant figures.
10. Repeat, check and compare
Repeat a measurement or use a second volume method where practical. Investigate anomalies, calculate a mean if repeated and compare the result with reference values.

Variables

This is primarily a determination practical rather than a cause-and-effect investigation. The object or material is the comparison variable; mass and volume are measured; density is calculated.

Variable type Variable
Comparison / independent variable Object or material being tested
Measured quantities Mass and volume
Calculated dependent quantity Density of the object
Control variables Same balance or checked balance zero; same unit system and calculation method; same volume technique for like-for-like comparisons; object dry before weighing; eye-level volume reading and complete submersion; same reference data source and similar temperature conditions.

Mass-volume graph extension variables

Variable type Variable
Independent variable Sample volume or object size
Dependent variable Mass
Control variables Same material, composition and temperature; same instruments and methods
Step-by-step density practical workflow for regular and irregular objects

Results and calculations

Regular objects

Object / shape Mass (g) Dimensions (cm) Volume (cm3) Density (g/cm3) Likely material
           
           
           

Irregular objects

Object Mass (g) Initial volume (mL) Final / collected volume (mL) Object volume (cm3) Density (g/cm3)
           
           
           

Example results

Object Measurements Mass (g) Volume (cm3) Density (g/cm3)
Aluminium cuboid 5.00 × 3.00 × 2.00 cm 81.0 30.0 2.70
Steel cylinder d = 2.00 cm, h = 5.00 cm 123.3 15.7 7.85
Irregular stone 50.0 mL to 77.0 mL 71.6 27.0 2.65

Worked example: regular cuboid

V = 5.00 × 3.00 × 2.00 = 30.0 cm3
ρ = 81.0 / 30.0 = 2.70 g/cm3

Worked example: irregular stone

V = 77.0 - 50.0 = 27.0 mL = 27.0 cm3
ρ = 71.6 / 27.0 = 2.65 g/cm3

Measuring the volume of an irregular object using a measuring cylinder and displacement can

Processing results and graph interpretation

Processing results

  • Record every raw measurement with a unit and consistent decimal places.
  • Calculate regular-object volume using the correct geometric formula.
  • For displacement, subtract initial volume from final volume or use the collected overflow.
  • Keep unrounded values through the calculation and round only the final density.
  • Calculate density for each repeat and a mean where repeated measurements are valid.
  • Identify anomalous readings and justify whether they should be repeated or excluded.
  • Compare with reference values using a percentage difference where appropriate.

Mass-volume graph

X-axis: volume
Y-axis: mass
For several samples of one material, draw a best-fit line and calculate its gradient using a large triangle. The gradient represents density because gradient = change in mass / change in volume.

Expected observations

  • Different-sized samples of the same material should give similar density values.
  • For equal volumes, the denser material has the greater mass.
  • The water-level increase or overflow volume equals the submerged object volume.
  • A narrow measuring cylinder usually gives more precise displacement readings than a very wide one.
  • Small objects often show larger percentage uncertainty because the displaced volume is close to the scale resolution.

Evidence-based conclusion

Under the conditions of the investigation, the density of each object is found by dividing its measured mass by its measured or calculated volume. Samples made from the same material should give similar values within measurement uncertainty. A value close to a reference density supports a material identification, but does not prove it because alloys, coatings, hollow spaces, porosity and measurement uncertainty can shift the result.

Density calculations worked examples and mass-volume graphs

Sources of error, improvements and evaluation

Sources of error

  • Balance not zeroed, on an uneven surface or affected by water on the pan.
  • Ruler misaligned with the object or a worn zero edge.
  • Parallax when reading a ruler or meniscus.
  • Callipers not closed to zero or squeezed too tightly.
  • Wrong dimension or diameter used instead of radius.
  • Object wet when its mass is measured.
  • Object not fully submerged or carrying trapped air bubbles.
  • Water lost by splashing, retained in the spout or missed by the cylinder.
  • String, hook or sinker adding uncorrected displaced volume.
  • Measuring cylinder too large for a small displaced volume.

Improvements

  • Zero or tare the balance before every object and check it with a known mass.
  • Use Vernier callipers or a micrometer for small dimensions.
  • Measure each dimension at several positions and calculate a mean.
  • Use a larger sample or several identical small items to reduce percentage uncertainty.
  • Choose the smallest suitable measuring cylinder and read at eye level.
  • Dry the object before weighing, lower it slowly and remove bubbles.
  • Place the displacement can on a stable stand inside a spill tray.
  • Repeat measurements and compare dimension and displacement methods for a regular object.

Reliability

Improve reliability by repeating measurements, calculating a mean, using the same apparatus and procedure, investigating anomalies, checking results with a second method and comparing results between groups using identical object sets.

Validity

The method is valid when the mass and volume belong to the same object and the chosen volume technique measures the full external volume intended. The object should not dissolve, absorb water, trap large bubbles or float unless a corrected method is used.

Accuracy

Choose suitable resolution, read scales at eye level, check zero errors, average diameter in more than one direction where appropriate, use thin string, keep all displaced water and report significant figures that reflect the least precise measurement.

Validity warning

A hollow, porous or composite object gives a bulk density for the whole object. Do not automatically identify the solid material from that value.

Uncertainty

For density, percentage uncertainties in mass and volume combine. A useful GCSE approximation is:

% uncertainty in density ≈ % uncertainty in mass + % uncertainty in volume

Random variation Systematic effects
Meniscus judgement Balance zero error
Small differences in dimension Calliper or ruler zero error
Drops retained or lost Graduated cylinder calibration bias
Bubbles attaching differently Consistent use of the wrong formula or unit

Higher-tier uncertainty example

If a measuring cylinder has ±0.5 mL uncertainty for each reading, an object volume found from two readings has an approximate absolute uncertainty of ±1.0 mL. For an 8.0 mL object volume, percentage uncertainty ≈ (1.0 / 8.0) × 100 = 12.5%. Combining several identical small objects increases total displaced volume while the scale uncertainty stays similar.

Advanced evaluation points (Grade 8-9)

1. Volume often dominates uncertainty
Small displacements or short dimensions can have a large percentage uncertainty. Larger samples and finer scales help.
2. Dimension uncertainty propagates
For a cuboid, percentage uncertainties in length, width and height approximately add. For a cylinder, radius is squared, so its uncertainty has a particularly strong effect.
3. Displacement measures external submerged volume
Sealed cavities and any submerged thread or hook are included. Open pores may fill with water.
4. Bubbles and clinging water bias results
Air bubbles increase displaced volume and make density too low; water on the object during weighing increases mass and makes density too high.
5. Density is sample-size independent only for a uniform material
A mass-volume graph should be linear when composition and structure are consistent.
6. A graph intercept can reveal systematic error
A non-zero mass or volume intercept may suggest tare, attached-component, offset or formula bias. Do not automatically force the line through the origin.
7. Reference densities are not exact universal constants
Alloys, polymers, woods and rocks can cover ranges; temperature and composition also matter.
8. Density alone may not uniquely identify a material
Identification is stronger when density is combined with other evidence such as colour, magnetism, conductivity or manufacturer information.

Troubleshooting guide

Problem Possible cause Solution
Balance will not read zero Wet pan, unstable bench, draught or low battery Dry the pan, move to a stable position, shield from draughts and check power.
Density is impossibly high or low Wrong units, wrong formula, wet object or incorrect volume Check raw measurements, unit conversions and the calculation before repeating.
No water leaves the displacement-can spout Water level below the spout or object not fully submerged Top up the can, allow it to settle, then fully submerge the object.
Water keeps dripping before the object is added Can was overfilled or moved Wait until dripping stops and do not disturb the can.
Object floats Object density is lower than water Use a sinker and correct for its volume, or choose a sinking object for the core method.
Object does not fit the cylinder Cylinder too narrow Use a displacement can or a wider vessel with a precise collection cylinder.
Repeated volumes are widely scattered Bubbles, inconsistent submersion or lost water Lower slowly, remove bubbles, use the same depth and collect every drop.
Very small object gives no clear volume change Displacement is close to scale resolution Use several identical objects together or a narrower cylinder.
Measured density does not match a reference material Object is alloyed, coated, hollow, porous or measured inaccurately Check the method and report a likely range rather than forcing an identification.

Quick examiner tip: when a density looks unusual, check the raw mass, raw volume and units first. Most errors come from volume calculation or displacement technique rather than from the density equation itself.

Common misconceptions and student mistakes

Common misconceptions

“Density means how heavy an object is.”
Density is mass per unit volume. Mass alone does not show density.
“A bigger object must be denser.”
For the same material, mass and volume increase together and density stays approximately constant.
“All dense materials simply have particles closer together.”
Particle mass, spacing, structure and empty space can all affect density.
“The final measuring-cylinder reading is the object volume.”
Object volume is the increase: final volume minus initial volume.
“1 mL and 1 cm3 are different units for different quantities.”
For volume, 1 mL is exactly equal to 1 cm3.
“If a density matches a table value, the material is proved.”
A close match supports an identification, but alloys, coatings, porosity and uncertainty can give similar values.
“A hollow metal object has the density of the metal.”
The experiment gives the average density of the whole object, including the hollow space.
“An object that floats has no weight.”
It has weight, but upthrust balances the weight when floating.

Common student mistakes

Common student mistake Consequence
Not zeroing the balance Adds a systematic mass error to every result.
Weighing a wet object Water adds mass and makes density too high.
Measuring from the end of a worn ruler rather than the zero mark Creates a systematic length and volume error.
Using diameter as radius in V = πr2h Makes the cylinder volume four times too large.
Mixing mm, cm and m Produces volume and density values with the wrong magnitude.
Reading the meniscus from above Introduces parallax error.
Using final water volume as object volume Overestimates object volume and underestimates density.
Not fully submerging the object Measures only the submerged volume.
Ignoring air bubbles or lost overflow Changes the measured displaced volume.
Rounding measurements before the final calculation Adds avoidable calculation error.
Claiming exact material identity from one density value Overstates what the evidence can support.

Extension investigations

Mass-volume graph: one material

  1. Select at least five samples of the same uniform material with different sizes.
  2. Measure the mass and volume of each sample using the same methods.
  3. Plot mass on the y-axis against volume on the x-axis.
  4. Draw a best-fit line and calculate its gradient using a large triangle.
  5. Compare the gradient with individual density calculations and reference data.

Floating object with a sinker

  1. Measure the floating object's mass.
  2. Measure the sinker volume by displacement.
  3. Attach the object to the sinker and fully submerge both.
  4. Measure their combined displaced volume.
  5. Object volume = combined volume - sinker volume.
  6. Calculate density from the object's own mass and corrected volume.

Liquid density

  1. Measure the mass of an empty measuring cylinder.
  2. Add a known volume of liquid.
  3. Measure the new total mass.
  4. Subtract to find the liquid mass.
  5. Calculate density using mass divided by volume.

Floating and sinking

Object less dense than the liquid: it floats because upthrust balances its weight before it is fully submerged.

Object with the same density as the liquid: it may remain suspended when fully submerged because upthrust balances weight.

Object more dense than the liquid: it sinks because its weight is greater than the upthrust.

Liquid Example density (g/cm3)
Oil 0.9
Water 1.0
Salt solution 1.1
Washing-up liquid / syrup 1.3

Important control for the sinker method: the sinker must remain fully submerged in both measurements, the floating object must be completely submerged in the combined measurement, and the string volume should be small or corrected.

Further extension questions

  • How closely do dimension and displacement methods agree for the same regular object?
  • Is density independent of sample size for several pieces of one material?
  • How does measuring-cylinder choice affect percentage uncertainty?
  • How do porosity, sealed cavities or water absorption affect bulk density?
  • How does the density of a liquid change with temperature?
  • Why is it easier to float in salt water than in pure water?
  • Why does oil float on water?
  • Why does a steel ship float even though steel is dense?
Liquid density and floating and sinking extension

GCSE required practical skills assessed

Practical skills

  • Safe handling of balances, glassware, water and dense objects.
  • Accurate measurement of length, diameter, mass and volume.
  • Selection of suitable apparatus and scale resolution.
  • Use of geometric formulae and displacement techniques.
  • Systematic recording of raw measurements and repeats.
  • Evidence-based conclusions and evaluation of method quality.

Mathematical skills

  • Substitute into and rearrange ρ = m / V.
  • Calculate volumes of cuboids and cylinders.
  • Convert mm, cm and m, and convert g/cm3 to kg/m3.
  • Calculate arithmetic means and percentage difference.
  • Plot two variables and calculate a gradient.
  • Use an appropriate number of significant figures.
Apparatus and technique How it is developed
AT 1 Use appropriate apparatus to make and record measurements of length, area, mass and volume accurately, then determine density.

GCSE specification links

This guide directly supports AQA GCSE Physics 8463 Required Practical Activity 5 and the corresponding density techniques in Combined Science. OCR identifies determining density of regular and irregular solids and liquids as Practical P1 in its purposeful practical menu. Examination board naming and numbering vary, so teachers should check the current local specification.

Risk assessment

Overall risk level: low. This practical presents a low level of risk when standard laboratory procedures are followed. Schools should complete their own risk assessment in accordance with local procedures.

Hazard Risk Control measures
Water spills Slip hazard or damage to electrical equipment Use trays and cloths; keep balances and leads dry; clean spills immediately.
Glass measuring cylinders Breakage and cuts Use stable bench positions; carry carefully; clear breakages with brush and pan.
Dense metal objects Dropped objects may injure feet or damage benches Use manageable masses, closed shoes and keep objects away from edges.
Sharp, rough or brittle objects Cuts, splinters or fragments Select safe samples; inspect before use; wear eye protection where appropriate.
Displacement can on a stand Can tips or water spills Use a wide stable support inside a spill tray and keep the spout clear.
Callipers and micrometers Pinch points or sharp tips Demonstrate gentle use and keep fingers clear of jaws.
String and objects in water Tangling or sudden object drop Use short prepared loops and lower objects slowly.
Liquid extension Exposure or ingestion Use only low-hazard liquids such as water or sugar solution; no tasting; wash hands.

Teacher / technician preparation notes

Technician tips for high success rates

  • Choose objects large enough to produce a clear balance and displacement reading.
  • Label each object and keep a checked reference-density list for the teacher.
  • Use regular objects with clean measurable faces and cylinders with a clearly known diameter.
  • Avoid absorbent, soluble, rusty, heavily coated or highly porous objects for the core task.
  • Test every balance, calliper and micrometer and check zero before the lesson.
  • Provide several measuring-cylinder sizes so students can justify the best choice.
  • Raise displacement cans high enough for a cylinder to fit beneath the spout.
  • Prepare thin string loops, spare batteries, cylinders, string and a replacement balance.
  • Prepare an example data set in case a group experiences equipment failure.

Before the lesson

  • Assemble and test one complete regular-object and one irregular-object station.
  • Check balance zero, ruler edges and calliper operation.
  • Prepare labelled object sets and a teacher reference table.
  • Choose measuring cylinders whose graduations suit the expected volumes.
  • Place displacement cans on stable stands inside spill trays.
  • Prepare student results tables and unit-conversion guidance.
  • Set out paper towels and identify a dry weighing area.
  • Prepare a clear risk briefing and spill procedure.

Pre-lesson trial

Measure one regular and one irregular object using the intended student apparatus. Check that the values are plausible, that the displaced volume is well above the scale resolution and that the can stops dripping reliably.

Teacher demonstration points

  1. How to zero or tare the balance.
  2. How to choose between a ruler, callipers and micrometer.
  3. How to measure from the zero mark and avoid parallax.
  4. How to distinguish radius from diameter.
  5. How to read the bottom of the meniscus at eye level.
  6. How to fill a displacement can and wait for dripping to stop.
  7. How to lower an object fully without bubbles or splashing.
  8. How to record raw readings and calculate volume difference.
  9. How to calculate density with units and sensible significant figures.
  10. How to compare with reference data without claiming certainty.

Key explanation: ask students which quantities are measured directly and which are calculated. Mass and dimensions or displaced volume are measured; object volume may be calculated; density is always derived from mass and volume.

Suggested lesson timing

Core regular and irregular object investigation - 60 minutes

Activity Time
Introduction and particle-model link 8 min
Safety briefing and demonstration 8 min
Regular-object measurements 12 min
Irregular-object displacement 15 min
Calculations and material comparison 10 min
Plenary and equipment check-in 7 min

Liquid / mass-volume graph extension - 50 to 60 minutes

Activity Time
Review controls and prepare liquid station 8 min
Collect mass at several liquid volumes 20 min
Plot graph and calculate gradient 15 min
Evaluation and floating/sinking discussion 12 min

Teacher assessment opportunities

  • Can students identify what is measured and what is calculated?
  • Can they select suitable apparatus and justify the resolution?
  • Do they zero the balance and measure dimensions correctly?
  • Do they read the meniscus at eye level and use full submersion?
  • Can they use the correct volume formula and density equation?
  • Do they keep units consistent and round appropriately?
  • Can they repeat, identify anomalies and compare with reference data?
  • Can they distinguish reliability, validity, accuracy and uncertainty?

Exam support

Common exam questions

1. Why must the balance be zeroed before measuring mass?
A non-zero reading creates a systematic error in every measured mass and density.
2. A cuboid is 4.0 cm × 3.0 cm × 2.0 cm and has mass 64.8 g. Calculate its density.
V = 24.0 cm3. ρ = 64.8 / 24.0 = 2.70 g/cm3.
3. Water rises from 35.0 mL to 47.5 mL. What is the object volume?
47.5 - 35.0 = 12.5 mL = 12.5 cm3.
4. Why should a meniscus be read at eye level?
To reduce parallax error and obtain the correct scale reading.
5. Why is a 25 mL cylinder often better than a 250 mL cylinder for a small object?
It usually has smaller scale divisions, giving lower absolute and percentage uncertainty.
6. Convert 2.70 g/cm3 to kg/m3.
2.70 × 1000 = 2700 kg/m3.
7. What does the gradient of a mass-volume graph represent?
Density, because gradient = change in mass / change in volume.
8. Why might measured density differ from a reference value?
Measurement uncertainty, alloy composition, coatings, porosity, hollow spaces, temperature or an incorrect material assumption.

High-value exam wording

State that the balance is zeroed, dimensions are measured with appropriate apparatus, the meniscus is read at eye level, the irregular object is completely submerged, displaced volume is found from a difference or collected overflow, measurements are repeated, and density is calculated with correct units and sensible significant figures.

Suggested plenary

Plenary question Expected answer
What does density mean? Mass per unit volume.
Why must an object be dry before its mass is measured? Water would add extra mass and make the calculated density too high.
How is the volume of an irregular solid found? By the increase in water volume or the volume of water displaced into a measuring cylinder.
Why use the smallest suitable measuring cylinder? Smaller scale divisions usually reduce percentage uncertainty.
What does the gradient of a mass-volume graph represent? Density.
Why can a hollow metal object have a low measured density? The calculation uses the whole external volume, including the hollow space.
Why does a close reference match not prove identity? Different materials can overlap and measurement uncertainty, alloys or porosity can shift the value.

Examiner advice summary

  • Define density as mass per unit volume and use ρ = m / V.
  • State what is measured directly and how volume is found.
  • Zero the balance and use suitable apparatus for dimensions or displacement.
  • Read the meniscus at eye level and fully submerge irregular objects.
  • Use the difference between final and initial volume.
  • Repeat measurements, investigate anomalies and calculate a mean where appropriate.
  • Keep units consistent and use sensible significant figures.
  • Plot mass on the y-axis against volume on the x-axis; gradient = density.
  • Do not claim exact material identity unless the evidence genuinely supports it.

Frequently asked questions

Why must the object be dry before weighing?

Water adds extra mass and makes the calculated density too high.

Why use radius rather than diameter in the cylinder formula?

The formula V = πr2h is written in terms of radius. Using the diameter as r makes the calculated volume four times too large.

Why can a hollow metal object have a low measured density?

The calculation uses the whole external volume, including the hollow space, so it gives the object's average or bulk density.

Why might a mass-volume graph not pass through the origin?

A non-zero intercept may indicate a systematic error such as a balance tare error, a constant attached component or a volume offset. The line should not automatically be forced through the origin.

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About this guide

This guide was written and reviewed by Better Equipped's technical team and further reviewed by former A Level Science Teachers. Our technical team draw on experience supplying practical science equipment to schools, colleges, laboratories and science departments throughout the UK. They include ex-school laboratory technicians and are here to support schools, colleges and laboratories. If you have feedback on this guide, we'd love to here it so please contact us. Don't forget we will be regularly updating our guides and resources on our Better-Resources Hub. If you would like us to cover a particular subject matter in these guides or have some top tips you'd like to share then again we'd love to hear from you.

Last reviewed and updated: August 2026

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