Who this is for: Cambridge IGCSE Physics (0625) students who want Mass and Weight — telling the difference, using W = mg and reading spring-balance questions — to become a reliable source of marks instead of interchangeable everyday words.
What query it owns: how to understand and revise Mass and Weight in Cambridge IGCSE Physics.
Why this is safe: this page owns the Mass and Weight revision-guide angle, while Tutopiya’s Mass and Weight subtopic page owns the learning resource and the free Mass and Weight quiz owns the practice.

Mass and Weight sit early in the Motion, Forces and Energy unit of Cambridge IGCSE Physics (0625), but the distinction still costs marks in every exam series. Examiners expect you to state that mass is the amount of matter in an object (measured in kilograms) while weight is the gravitational force on that object (measured in newtons). This guide explains the definitions, the W = mg relationship, the question types that actually appear, and where to practise each skill.

Key takeaways

• Mass is measured in kg; it does not change when you move to another planet.
• Weight is a force measured in N; it depends on gravitational field strength g.
• Use W = mg with g ≈ 10 N/kg on Earth unless the question gives another value.
• A spring balance measures weight; a pan balance compares mass.

What is Mass and Weight in Cambridge IGCSE Physics?

Mass is a scalar quantity — the amount of matter in a body — measured in kilograms (kg). Weight is the force exerted on that mass by a gravitational field, measured in newtons (N). The link is W = mg, where g is gravitational field strength in N/kg. In Cambridge IGCSE Physics, mass and weight questions appear alongside forces, density and motion graphs, and examiners penalise students who swap the units or treat weight as if it were mass.

You can read the full explanation, worked examples and notes on Tutopiya’s Mass and Weight subtopic page before you attempt questions.

The core ideas you must master

These four ideas appear again and again. Learn what each one means and the exam phrasing that signals it.

Idea	What it means	How the exam uses it
Mass	Amount of matter; unit kg	”State the mass of the object”
Weight	Gravitational force; unit N	”Calculate the weight of the block”
Gravitational field strength	Force per unit mass; g in N/kg	”On the Moon, g = 1.6 N/kg. Find the weight.”
Measuring instruments	Pan balance vs spring balance	”Which instrument measures weight?”

How to use W = mg — step by step

The safest method works for every calculation question in this subtopic.

1. Identify whether the question asks for mass or weight — check the unit in the answer line.
2. Write W = mg and state the value of g (usually 10 N/kg on Earth).
3. Substitute mass in kg and multiply by g.
4. Give the answer in newtons with the unit N.
5. Check: weight on Earth should be roughly ten times the mass in kg.

Once you have worked through a few, test yourself with the free Mass and Weight quiz — it tells you fast whether the method has actually stuck.

Earth vs Moon: which value of g does the question want?

Students lose marks by using g = 10 N/kg when the question states a different field strength, or by saying mass changes on the Moon.

Situation	What to do	Typical signal words
Object on Earth	Use g = 10 N/kg unless told otherwise	”on Earth”, no g stated
Object on Moon or another planet	Use the g value given in the question	”on the Moon, g = 1.6 N/kg”
Comparing two locations	Mass stays the same; weight changes	”same object taken to the Moon”
Instrument question	Match instrument to quantity measured	”spring balance”, “pan balance”

Mass and Weight in past-paper wording: command words that matter

Most lost marks come from misreading the command word or writing kg when the answer should be N. These are the command words you will see and what each one demands.

Command word / phrase	What the question wants	Typical Mass and Weight stem
State / Define	Give a precise definition	”State what is meant by mass.”
Calculate / Work out	Use W = mg with shown working	”Work out the weight of a 5 kg object.”
Explain	Link ideas — mass constant, weight varies	”Explain why weight changes on the Moon but mass does not.”
Suggest	Apply knowledge to a new context	”Suggest which instrument measures weight.”
Give your answer to …	Round as instructed	”Give your answer to 2 significant figures.”

Worked exam-style stems (how to answer the wording)

Practising the wording — not just the formula — is what method marks reward. Here is how three real-style stems are answered.

1. “A student has a mass of 60 kg. Calculate her weight on Earth. Take g = 10 N/kg.” W = mg = 60 × 10 = 600 N. Mark-scheme reward: formula stated, correct substitution, unit N.
2. “The same student travels to the Moon where g = 1.6 N/kg. State her mass on the Moon.” Mass is still 60 kg — mass does not change with location. Reward: correct value with unit kg; no calculation needed.
3. “A spring balance reads 25 N. Calculate the mass of the object. Take g = 10 N/kg.” Rearrange: m = W/g = 25/10 = 2.5 kg. Reward: rearrangement shown before the final answer.

When you can recognise the wording instantly, work the full set on the Motion, Forces and Energy topical past-paper questions and the Mass and Weight quiz to lock the method in.

How Mass and Weight connects to the rest of Motion, Forces and Energy

Weight is a force — it appears on free-body diagrams in Forces and feeds into gravitational potential energy in Energy, Work and Power. Mass is essential for Density calculations and Momentum. When you are ready to move on, the Cambridge IGCSE Physics resource hub lets you jump straight from a weak subtopic into the next.

Common mistakes students make

• Writing weight in kg or mass in N.
• Saying mass changes when an object is taken to the Moon.
• Using g = 9.8 or g = 10 inconsistently within the same question.
• Treating a spring balance reading as mass without converting via W = mg.
• Confusing weight with pressure in later topics.

When you need more support

If Mass and Weight questions keep tripping you up — especially rearranging W = mg or instrument questions — work through the Motion, Forces and Energy topical past-paper questions and the Mass and Weight quiz to pinpoint the exact gap, then get focused help from a Cambridge IGCSE Physics tutor to fix it quickly.

Frequently asked questions

Is Mass and Weight hard in Cambridge IGCSE Physics? No — the ideas are straightforward. Marks are lost when students swap units, forget that mass is constant, or use the wrong value of g.

What is the difference between mass and weight? Mass is the amount of matter (kg). Weight is the gravitational force on that mass (N), calculated using W = mg.

Does mass change on the Moon? No. Only weight changes because gravitational field strength is smaller on the Moon.

How do I revise Mass and Weight effectively? Read the subtopic notes, practise W = mg in both directions, then take the Mass and Weight quiz. Revisit any Moon-comparison questions you got wrong before moving on.

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