What is the difference between mass and weight in the context of Cambridge IGCSE Coordinated Science?

In Cambridge IGCSE Coordinated Science, mass is defined as the amount of matter in an object and is measured in kilograms (kg). It is a scalar quantity and does not change regardless of location. Weight, on the other hand, is the force exerted by gravity on an object and is measured in newtons (N). Weight is a vector quantity and can vary depending on the gravitational field strength, such as on different planets.

How do you calculate weight from mass in the IGCSE Coordinated Science curriculum?

To calculate weight from mass in the IGCSE Coordinated Science curriculum, you use the formula: Weight (N) = Mass (kg) × Gravitational field strength (N/kg). On Earth, the gravitational field strength is approximately 9.8 N/kg. Therefore, if you know the mass of an object, you can multiply it by 9.8 to find its weight.

Why does mass remain constant while weight changes in different locations?

Mass remains constant because it is a measure of the amount of matter in an object, which does not change regardless of location. Weight changes because it depends on the gravitational field strength, which can vary in different locations. For example, the gravitational pull on the Moon is weaker than on Earth, so an object will weigh less on the Moon even though its mass remains the same.

What units are used for mass and weight in the Cambridge IGCSE Coordinated Science syllabus?

In the Cambridge IGCSE Coordinated Science syllabus, mass is measured in kilograms (kg), which is the standard unit of mass in the International System of Units (SI). Weight is measured in newtons (N), which is the SI unit for force. This distinction is important for understanding the concepts of mass and weight in physics.

How does understanding mass and weight help in studying motion in Coordinated Science?

Understanding mass and weight is crucial for studying motion in Coordinated Science because they influence how objects move under the influence of forces. Mass affects an object's inertia, which is its resistance to changes in motion. Weight, being a force, directly affects how objects accelerate under gravity. This knowledge helps in analyzing motion, predicting how objects will behave under different forces, and solving problems related to dynamics.

Why is "Stating that weight is measured in kilograms" a common mistake in Mass and Weight?

Why it happens: In everyday language 'weight' is used to mean mass. How to avoid it: Mass → kilograms (kg). Weight → newtons (N). A bathroom scale measures your weight but is calibrated to display mass.

Why is "Using $g = 10\,\text{m/s}^{2}$ when $g$ on another planet is given" a common mistake in Mass and Weight?

Why it happens: Students default to Earth's value without checking the question. How to avoid it: Read the question for the stated value of g; it will be different for Moon, Mars, etc.

Why is "Describing centre of gravity as 'where the weight is balanced' rather than 'where weight acts'" a common mistake in Mass and Weight?

Why it happens: Imprecise recall of the definition. How to avoid it: Learn the exact phrasing: 'the point at which the entire weight of the object can be considered to act'.

Cambridge IGCSE Coordinated Science (0654)

Mass and Weight

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Short Notes - Mass and Weight

Detailed Study Notes

Detailed notes on Motion for Cambridge IGCSE Coordinated Science, covering key concepts, explanations, examples, and exam-focused revision points.

Mass and Weight — Cambridge IGCSE Coordinated Science 0654

Mass and weight are frequently confused. Cambridge specifically tests the scalar/vector distinction, the formula W = mg, and how these quantities change (or don't) in different gravitational fields such as on the Moon.

At a glance

Mass (kg): amount of matter. Scalar. CONSTANT everywhere in the universe.
Weight (N): gravitational force on mass. Vector. Changes with gravitational field strength g.
W = mg. On Earth g = 9.81 N/kg ≈ 10 N/kg. On Moon g ≈ 1.6 N/kg.
Gravitational field strength g = 9.81 N/kg on Earth's surface; also equals free-fall acceleration (9.81 m/s²) — same value, different unit.
Measured with: mass → balance (beam balance). Weight → newton meter / spring balance.

What you’ll learn

Mapped to the Cambridge IGCSE 0654 syllabus (2025-2027).

P1.3a — Define mass and weight and distinguish between them.
P1.3b — Recall and use the equation W = mg.
P1.3c — Describe how mass and weight differ on other planets.

Mass vs Weight

Mass is what you are; weight is the force gravity exerts on you.

Mass:

Amount of matter in an object
Scalar quantity (no direction)
Unit: kilogram (kg)
Constant — does not change with location (same on Earth, Moon, space)
Measured with a balance (compares with known masses)

Weight:

Gravitational force acting on an object (force due to gravity)
Vector quantity (acts downward toward centre of Earth)
Unit: newton (N)
Changes with gravitational field strength: W = mg
- W = weight (N), m = mass (kg), g = gravitational field strength (N/kg)

g on different bodies:

Location	g (N/kg)
Earth surface	9.81 ≈ 10
Moon surface	1.6
Mars surface	3.7
Deep space	≈ 0

Example: A person with mass 60 kg on Earth: W = 60 × 9.81 = 589 N On the Moon: W = 60 × 1.6 = 96 N (but mass is STILL 60 kg)

Measuring instruments:

Mass → beam balance (works anywhere, since both sides experience same g)
Weight → newton meter / spring balance (measures force; calibrated for Earth's g)

Mass (kg): constant everywhere. Weight (N): depends on g. W = mg.
On Moon: same mass, less weight (g ≈ 1.6 N/kg vs 9.81 N/kg on Earth).
Newton meter measures weight; beam balance measures mass.

Gravitational Field Strength

g is both the free-fall acceleration (m/s²) and the gravitational field strength (N/kg) — same numerical value, different contexts.

Gravitational field strength (g):

Defined as force per unit mass: g = W/m
Unit: N/kg (numerically equal to m/s² for free-fall acceleration)
On Earth's surface: g = 9.81 N/kg

Why g varies:

g decreases with distance from Earth's centre (inverse square relationship)
g also varies slightly across Earth's surface (Earth is not a perfect sphere)
g depends on the mass of the planet — more massive planet → stronger g

Inertia:

Inertia is the resistance of an object to changes in motion
Greater mass → greater inertia
Inertia depends only on mass, not weight or gravity
This is why a beam balance works on the Moon: both objects have the same inertia, so the equal-arm balance gives the correct mass comparison

g = W/m in N/kg; same value as free-fall acceleration in m/s².
g decreases with distance from the planet's centre.
Inertia depends on mass only — not weight.

Quick recap

Mass = amount of matter (kg, constant). Weight = gravitational force (N, W = mg, varies with g).
On Earth: g = 9.81 N/kg. On Moon: g ≈ 1.6 N/kg.
A 10 kg object weighs 98 N on Earth and 16 N on the Moon; mass stays 10 kg.

Memorise this

Verbatim phrases and definitions Cambridge mark schemes credit.

W = mg — weight (N) = mass (kg) × gravitational field strength (N/kg).
g on Earth — 9.81 N/kg (or 10 N/kg for estimates).
Mass — scalar, constant everywhere; measured with beam balance.
Weight — vector (downward), changes with location; measured with newton meter.

How it’s examined

Paper 4: 'Calculate the weight of a 3.0 kg object on the Moon where g = 1.6 N/kg' (2 marks — W = 3.0 × 1.6 = 4.8 N). 'Explain why the mass of an astronaut does not change when they travel from Earth to the Moon but their weight does' (2 marks — mass is amount of matter / constant; weight depends on gravitational field strength which is less on the Moon). MCQ: distinguishing mass from weight.

Sources: Cambridge IGCSE Coordinated Sciences 0654 syllabus 2025-2027 (P1); 0654 Examiner Reports 2022-2024. Last reviewed 2026-05-14.

Take this whole topic with you

Step-by-step worked examples — Mass and Weight

Step-by-step solutions to past-paper-style questions on mass and weight, written exactly the way a tutor would explain them at the board.

1Calculating weight from mass
Core• weight, W=mg
Question
An astronaut has a mass of $75\,\text{kg}$ . Calculate their weight on Earth where $g = 10\,\text{N/kg}$ .
Step-by-step solution
1. Step 1
  Use $W = mg$ .
  $W = 75 \times 10 = 750\,\text{N}$
Answer
$W = 750\,\text{N}$
2Weight on the Moon
Extended• gravitational field strength, Moon
Question
The same astronaut (mass $75\,\text{kg}$ ) lands on the Moon where $g_{\text{Moon}} = 1.6\,\text{N/kg}$ . Find their weight on the Moon and explain why their mass is unchanged.
Step-by-step solution
1. Step 1
  Weight on Moon using $W = mg_{\text{Moon}}$ .
  $W_{\text{Moon}} = 75 \times 1.6 = 120\,\text{N}$
2. Step 2
  Mass is the quantity of matter in the astronaut. It does not depend on the gravitational field and is the same everywhere in the universe.
Answer
$W_{\text{Moon}} = 120\,\text{N}$ ; mass remains $75\,\text{kg}$ because mass is independent of gravitational field strength.
Examiner tip
Examiners penalise answers that say 'mass changes on the Moon'. Always state that mass is an intrinsic property.
3Finding the centre of gravity of an irregular lamina
Challenge• centre of gravity, experimental
Question
Describe an experiment to locate the centre of gravity of an irregularly shaped piece of card.
Step-by-step solution
1. Step 1
  Make three small holes near the edge of the card. Suspend the card from a pin through hole A so it can swing freely.
2. Step 2
  Hang a plumb line from the same pin. When stationary, draw a line on the card along the plumb line. This line passes through the centre of gravity.
3. Step 3
  Repeat from holes B and C. The three lines intersect at the centre of gravity.
4. Step 4
  Verify: balance the card on a pencil tip — it should balance at the marked point.
Answer
The centre of gravity is the intersection of the three plumb-line traces.
Examiner tip
State clearly that the plumb line is used and why it is always vertical (gravity acts downward through the CoG).

Key Formulae — Mass and Weight

The formulae you need to memorise for mass and weight on the Cambridge IGCSE 0654 paper, with every variable defined in plain English and a note on when to use it.

Weight
$W = mg$
$W$
weight (N)
$m$
mass (kg)
$g$
gravitational field strength (N/kg)
When to use
Converting between mass (kg) and weight (N) on any planet or moon.
Example
$W = 75\,\text{kg} \times 10\,\text{N/kg} = 750\,\text{N}$

Key Definitions and Keywords — Mass and Weight

Definitions to memorise and the exact keywords mark schemes credit for mass and weight answers — sharpened from recent examiner reports for the 2026 0654 sitting.

Mass
Examiner keyword
The quantity of matter in an object. It is a scalar quantity measured in kilograms (kg) and is the same everywhere in the universe.
Weight
Examiner keyword
The gravitational force acting on an object. It is a vector quantity measured in newtons (N) and varies with gravitational field strength.
Related: mass, gravitational field strength
Gravitational field strength ( $g$ )
Examiner keyword
The gravitational force per unit mass at a point in a gravitational field. SI unit: N/kg (equivalent to m/s²). On Earth's surface, $g \approx 10\,\text{N/kg}$ .
Centre of gravity
Examiner keyword
The single point at which the entire weight of an object can be considered to act.
Example
For a uniform ruler, the centre of gravity is at the midpoint.

Common Mistakes and Misconceptions — Mass and Weight

The traps other students keep falling into on mass and weight questions — taken from recent Cambridge IGCSE 0654 examiner reports and mark schemes — and how to avoid them.

✕Stating that weight is measured in kilograms
Why it happens
In everyday language 'weight' is used to mean mass.
How to avoid it
Mass → kilograms (kg). Weight → newtons (N). A bathroom scale measures your weight but is calibrated to display mass.
✕Using $g = 10\,\text{m/s}^{2}$ when $g$ on another planet is given
Why it happens
Students default to Earth's value without checking the question.
How to avoid it
Read the question for the stated value of $g$ ; it will be different for Moon, Mars, etc.
✕Describing centre of gravity as 'where the weight is balanced' rather than 'where weight acts'
Why it happens
Imprecise recall of the definition.
How to avoid it
Learn the exact phrasing: 'the point at which the entire weight of the object can be considered to act'.

Mass and Weight — frequently asked questions

The things students keep getting wrong in this sub-topic, answered.

Location

g (N/kg)

Earth surface

9.81 ≈ 10

Moon surface

1.6

Mars surface

3.7

Deep space

≈ 0

Gravitational field strength (g):

Defined as force per unit mass: g = W/m
Unit: N/kg (numerically equal to m/s² for free-fall acceleration)
On Earth's surface: g = 9.81 N/kg

Why g varies:

g decreases with distance from Earth's centre (inverse square relationship)
g also varies slightly across Earth's surface (Earth is not a perfect sphere)
g depends on the mass of the planet — more massive planet → stronger g

Inertia:

Inertia is the resistance of an object to changes in motion
Greater mass → greater inertia
Inertia depends only on mass, not weight or gravity
This is why a beam balance works on the Moon: both objects have the same inertia, so the equal-arm balance gives the correct mass comparison

Mass and Weight

Short Notes - Mass and Weight

Detailed Study Notes

At a glance

What you’ll learn

Mass vs Weight

Gravitational Field Strength

Quick recap

Memorise this

How it’s examined

Take this whole topic with you

1Calculating weight from mass

2Weight on the Moon

3Finding the centre of gravity of an irregular lamina

Weight

Mass

Weight

Gravitational field strength (ggg)

Centre of gravity

✕Stating that weight is measured in kilograms

✕Using g=10 m/s2g = 10\,\text{m/s}^{2}g=10m/s2 when ggg on another planet is given

✕Describing centre of gravity as 'where the weight is balanced' rather than 'where weight acts'

Mass and Weight — frequently asked questions

Mass and Weight

Short Notes - Mass and Weight

Detailed Study Notes

At a glance

What you’ll learn

Mass vs Weight

Gravitational Field Strength

Quick recap

Memorise this

How it’s examined

Take this whole topic with you

1Calculating weight from mass

2Weight on the Moon

3Finding the centre of gravity of an irregular lamina

Weight

Mass

Weight

Gravitational field strength (ggg)

Centre of gravity

✕Stating that weight is measured in kilograms

✕Using g=10 m/s2g = 10\,\text{m/s}^{2}g=10m/s2 when ggg on another planet is given

✕Describing centre of gravity as 'where the weight is balanced' rather than 'where weight acts'

Mass and Weight — frequently asked questions

Gravitational field strength ( $g$ )

✕Using $g = 10\,\text{m/s}^{2}$ when $g$ on another planet is given

Gravitational field strength ( $g$ )

✕Using $g = 10\,\text{m/s}^{2}$ when $g$ on another planet is given