What is density and how is it calculated in the context of IB MYP Science?

Density is a measure of how much mass is contained in a given volume. It is calculated using the formula: Density = Mass/Volume. In the IB MYP Science curriculum, understanding density is crucial as it helps explain various phenomena related to motion, forces, and energy. For example, density differences can explain why objects float or sink in fluids.

How does density relate to the concepts of motion and forces in IB MYP Science?

Density plays a significant role in understanding motion and forces. In IB MYP Science, students learn that objects with different densities experience different buoyant forces when immersed in a fluid. This affects their motion, such as sinking or floating. Additionally, density differences can lead to convection currents, which are important in understanding energy transfer in fluids.

Why is understanding density important for studying energy transformations in IB MYP Science?

Understanding density is important for studying energy transformations because it affects how substances interact with energy. For example, in IB MYP Science, students explore how denser materials might conduct heat more efficiently, influencing thermal energy transfer. Additionally, density variations in the atmosphere or oceans can drive large-scale energy transformations, such as weather patterns and ocean currents.

How can density be experimentally determined in an IB MYP Science lab?

In an IB MYP Science lab, density can be experimentally determined by measuring the mass and volume of a substance. The mass can be measured using a balance, while the volume can be determined by water displacement for irregular objects or by measuring dimensions for regular shapes. The density is then calculated using the formula Density = Mass/Volume. This hands-on approach helps students understand the practical applications of density.

What are some real-world applications of density that are relevant to IB MYP Science students?

Real-world applications of density that are relevant to IB MYP Science students include understanding why ships float, how hot air balloons rise, and the principles behind hydraulic systems. Density is also crucial in environmental science for understanding phenomena like oil spills, where less dense oil floats on water, affecting ecosystems. These applications help students connect theoretical knowledge with practical scenarios.

Why is "Treating heavy objects as automatically denser." a common mistake in Density?

Why it happens: In everyday language we use "heavy" to mean both massive and dense. How to avoid it: Compare mass-per-volume. A large block of foam can be heavier than a small lump of lead but is much less dense.

Why is "Forgetting to convert g/cm³ ↔ kg/m³ when MYP asks for SI units." a common mistake in Density?

Why it happens: Lab work is naturally in g and cm³, so students leave the answer that way. How to avoid it: Multiply g/cm³ by 1 000 to get kg/m³, or divide kg/m³ by 1 000 to get g/cm³.

Why is "Reading a higher water level when the object is only partially submerged." a common mistake in Density?

Why it happens: Floating objects are hard to push under, so students record before the object is fully under. How to avoid it: Use a thin sinker rod or a Eureka can. The object must be fully submerged for the displacement to equal its volume.

Displacement method for irregular solids

Learning Portal

Learning Platform

Launching your learning experience…

Report issue

Density — IB MYP Sciences: ρ = m/V, regular and irregular solids, floating and sinking

Density tells you how much mass is packed into a volume. This MYP Sciences study note covers the formula ρ = m/V, units (kg/m³ and g/cm³), the displacement method for irregular solids, why dense objects sink and less-dense ones float, and a full investigation plan that meets MYP criteria B, C and D.

At a glance

Density ρ = mass ÷ volume. SI units kg/m³; commonly g/cm³ in MYP labs.
Water has density 1 000 kg/m³ = 1 g/cm³.
An object floats in a fluid if its density is lower than the fluid's density.
Volume of a regular solid is found from its dimensions; irregular solids use displacement.
Density of a gas can be changed easily (compress it); density of a solid is essentially fixed.
1 g/cm³ = 1 000 kg/m³ (a useful conversion).

What you’ll learn

Mapped to the IB MYP Sciences subject guide (2026 onwards).

MYP Sciences A — State the formula for density and its units.
MYP Sciences A — Predict whether an object will float or sink in a given fluid.
MYP Sciences B — Plan a method to measure the density of a regular and an irregular solid.
MYP Sciences C — Process density data with appropriate sig figs and uncertainty.
MYP Sciences D — Evaluate the role of density in real-world systems (ship design, hot-air balloons, ice on ponds).

What is density?

Density is how much mass is squeezed into a given volume.

Imagine two boxes of identical size. One is full of feathers; the other is full of steel ball bearings. They look the same — but lifting them tells you immediately the steel box has far more mass crammed into the same volume. The steel box is denser.

$\rho = \frac{m}{V}$

where ρ ("rho") is density, m is mass and V is volume. The standard SI units are kg/m³, but in MYP labs you will more often use g/cm³ because the numbers are friendlier:

Material

Finding volume — regular vs irregular shapes

Use a ruler for regular solids; use water displacement for irregular ones.

For a regular solid (cube, cuboid, sphere, cylinder), measure dimensions with a ruler or vernier calliper and use the geometry formula:

Cube / cuboid: V = l × w × h
Cylinder: V = π r² h
Sphere: V = (4/3) π r³

For an irregular solid (a pebble, a metal nut), use the water-displacement method:

Two measuring cylinders showing water level before and after a stone is added

Fill a measuring cylinder partly with water and record the level V₁.
Carefully add the irregular object so it is fully submerged.
Record the new water level V₂.
The object's volume is V₂ − V₁.

The object must sink fully and must not absorb water. For a floating object, push it under with a thin metal rod (whose volume is negligible) or use a "Eureka can" overflow method.

Regular: use geometry (V = l × w × h, π r² h, etc.).

Why things float — or sink

An object floats in a fluid if it is less dense than that fluid.

Compare densities to predict floating or sinking. An object floats when its density is lower than the density of the fluid it sits in.

A cork (0.24 g/cm³) floats in water (1.00 g/cm³).
A steel nail (~7.87 g/cm³) sinks in water but a steel ship floats — because the ship's overall density (including the air inside its hull) is less than 1 g/cm³.
Ice (0.92 g/cm³) floats on water — which is why lakes freeze from the top down, keeping fish alive beneath.

This is why shape matters, not just material. A pile of bricks sinks; a sealed empty box made of the same bricks would float if its total mass divided by its total volume (including the air inside) is less than 1 g/cm³.

For floating, the upthrust (buoyancy) from the fluid equals the object's weight. The fraction of the object submerged equals the ratio of the object's density to the fluid's density. Ice floats with about 92% under water because its density is 0.92 × water's density.

Float if ρ_object < ρ_fluid; sink if ρ_object > ρ_fluid.
Shape (hollow vs solid) changes overall density.
Submerged fraction = ρ_object / ρ_fluid.

Quick recap

ρ = m / V; SI units kg/m³, lab units g/cm³.
1 g/cm³ = 1 000 kg/m³.
Regular solids: volume from geometry. Irregular solids: water-displacement.
Float if density is less than the fluid's density.
Water has density 1.00 g/cm³; ice 0.92 g/cm³; air 0.0012 g/cm³.

Memorise this

Verbatim phrases and definitions MYP criterion-A markschemes credit.

Density ρ = m / V
Water: ρ = 1 000 kg/m³ = 1 g/cm³
1 g/cm³ = 1 000 kg/m³
Float when ρ_object < ρ_fluid

Sources: IB MYP Sciences guide (IBO, official subject guide). Last reviewed 2026-05-25.

Density – Study Notes & Past Paper Style Questions | IB MYP Sciences (Years 1-5) | Tutopiya

Air (room temp.)	0.0012	1.2
Cork	~0.24	240
Ice	0.92	920
Water (4 °C)	1.00	1 000
Aluminium	2.70	2 700
Iron	7.87	7 870
Lead	11.3	11 300
Gold	19.3	19 300

Density

Detailed Study Notes

Take this whole topic with you

Density — frequently asked questions

Density — IB MYP Sciences: ρ = m/V, regular and irregular solids, floating and sinking

At a glance

What you’ll learn

What is density?

Finding volume — regular vs irregular shapes

Why things float — or sink

Quick recap

Memorise this

Step-by-step worked examples — Density

1Density of a metal block

2Density by displacement

3Will it float?

Key Formulae — Density

Density

Density unit conversion

Key Definitions and Keywords — Density

Density

Displacement method

Upthrust (buoyancy)

Eureka (overflow) can

Common Mistakes and Misconceptions — Density

✕Treating heavy objects as automatically denser.

✕Forgetting to convert g/cm³ ↔ kg/m³ when MYP asks for SI units.

✕Reading a higher water level when the object is only partially submerged.