Interactive practical

Measuring density

Measure an aluminium block with a ruler, find a stone's volume by displacement and weigh a liquid in a measuring cylinder, then calculate each density and compare the block with the data-book value.

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GCSE Physics

Measuring density

CCEA 1210 — matched to your course.

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Available question marks5

Practical focus

Measure mass and volume independently, then use ρ = m/V.

Practical method

Aim

Determine the density of regular and irregular solids using ρ = \(\dfrac{m}{V}\).

Variables

Independent variable: the object (material) being tested
Dependent variable: density, calculated from measured mass and volume
Control variables: the same zeroed balance; the same measuring cylinder or displacement can; water at room temperature.

Apparatus

Top-pan balance (0.1 g)
Ruler (1 mm) and vernier caliper (0.1 mm)
Measuring cylinder (1 cm³)
Displacement (eureka) can
Thread

Method

Zero the balance and measure the mass of the object.
Regular solid: measure length, width and height with a ruler or vernier caliper, repeating each in different places, and calculate volume = length × width × height.
Irregular solid: fill a displacement can until water runs from the spout, place a measuring cylinder under the spout and lower the object in on a thread. The volume of water collected equals the volume of the object.
Alternatively, record the water level in a measuring cylinder before and after the object is fully submerged; the volume is the difference.
Read the bottom of the meniscus at eye level and check that no air bubbles cling to the object.
Calculate density = mass ÷ volume and compare with data-book values.

Sample results

Results for an aluminium block and a stone (cylinder readings 50.0 cm³ before and 68.0 cm³ after for the stone).

Object	Mass / g	Volume / cm³	Density / g/cm³
Aluminium block (5.0 × 4.0 × 2.0 cm)	108.0	40.0	2.70
Stone	46.8	18.0	2.60

Analysis

Block: V = 5.0 × 4.0 × 2.0 = 40.0 cm³, so ρ = 108.0 ÷ 40.0 = 2.70 g/cm³ = 2700 kg/m³, matching aluminium. Stone: V = 68.0 − 50.0 = 18.0 cm³, so ρ = 46.8 ÷ 18.0 = 2.60 g/cm³. To convert g/cm³ to kg/m³, multiply by 1000.

Errors and improvements

Problem	Effect	Improvement
Air bubbles on the stone	Volume reading too large, density too small	Lower the object slowly and tap it to release bubbles
Reading the meniscus from above or below (parallax)	Volume reading wrong	Read the bottom of the meniscus at eye level
1 cm³ cylinder resolution with a small volume	Large percentage uncertainty	Use a narrower cylinder with finer divisions, or a larger sample

Risk assessment

Hazard	Risk	Control measure
Water spilled on the floor	Slipping	Mop up spills straight away
Heavy objects dropped	Injury to feet or breaking glassware	Lower objects gently on a thread

Common mistakes

Using the total water level instead of the change in level.
Mixing grams with kilograms or cm³ with m³.
Forgetting to zero the balance.

Worked analysis

A block measures 4.0 cm × 3.0 cm × 2.5 cm and has a mass of 81.0 g. Volume = 4.0 × 3.0 × 2.5 = 30.0 cm³. Density = 81.0 ÷ 30.0 = 2.7 g/cm³ = 2700 kg/m³.

Common misconception

A heavier object is not necessarily denser. Density compares mass with volume, so a large piece of wood can be heavier than a small piece of iron but still less dense.

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