Physical quantities
Cambridge A-Level Physics (9702) · Unit 1: Physical quantities and units · 7 flashcards
Physical quantities is topic 1.1 in the Cambridge A-Level Physics (9702) syllabus , positioned in Unit 1 — Physical quantities and units , alongside SI units, Errors and uncertainties and Scalars and vectors. In one line: All physical quantities consist of a numerical magnitude (the 'how much') and a unit (the 'what' of the measurement).
Marked as AS Level: examined at AS Level in Paper 1 (Multiple Choice), Paper 2 (AS Structured Questions) and Paper 3 (Advanced Practical Skills). The same content may also be assumed in Paper 4 (A Level Structured Questions).
The deck below contains 7 flashcards — 3 definitions and 4 key concepts — covering the precise wording mark schemes reward. Use the 3 definition cards to lock down command-word answers (define, state), then move on to the concept and calculation cards to handle explain, describe, calculate and compare questions.
Some cards in this deck are on other syllabus topics: 1.2 SI units. Each card is labelled with its topic.
What two components define all physical quantities
All physical quantities consist of a numerical magnitude (the 'how much') and a unit (the 'what' of the measurement).
What the Cambridge 9702 syllabus says
2025-2027 syllabus, in our words · AS LevelWhat the syllabus expects you to be able to do in this topic, in plain English. For the exact wording, see the official syllabus (PDF).
- Recognise that every physical quantity is made up of a number (its magnitude) together with a unit.
- Estimate sensible values for the physical quantities covered in this syllabus.
Also in this deck: 1.2 SI units
- Recall these SI base quantities with their units: length (m), mass (kg), time (s), electric current (A) and temperature (K).
- Express a derived unit in terms of SI base units by multiplying or dividing them, and apply the appropriate derived units to the quantities in this syllabus.
- Check whether a physical equation is homogeneous by comparing the SI base units on each side.
- Recall the following prefixes and their symbols, and use them to show decimal multiples and submultiples of both base units and derived units: tera (T), giga (G), mega (M), kilo (k), deci (d), centi (c), milli (m), micro (μ), nano (n), pico (p).
Cambridge syllabus keywords to use in your answers
These are the official Cambridge 9702 terms tagged to this section. Mark schemes credit responses that use the exact term — weave them into your answers verbatim rather than paraphrasing.
Tips to avoid common mistakes in these topics
- › Ensure you distinguish between a quantity (like spring constant) and its units (like N m⁻¹); remember all physical quantities have a magnitude and a unit.
- › Express every unit in the term (e.g., N = kg m s⁻²) then combine them; moment of force SI base units are kg m² s⁻².
- › Check that the units used in a calculation are consistent, particularly for prefixes like k, μ, or M, before finalizing your answer.
- › Check homogeneity using the SI base units (kg, m, s, A, K); convert mass to kg first.
- › Memorize SI prefixes: Giga (G) is 10 to the power of 9. Use standard form throughout your calculations.
Topic 1.1 · Physical quantities
What two components define all physical quantities?
All physical quantities consist of a numerical magnitude (the 'how much') and a unit (the 'what' of the measurement).
Topic 1.1 · Physical quantities
Estimate the typical walking speed of a human.
A reasonable estimate for the typical walking speed of a human is around 1.5 m/s. Speeds can vary slightly depending on the person and terrain.
Topic 1.1 · Physical quantities
Estimate the mass of a standard office chair.
A reasonable estimate for the mass of a standard office chair is between 10 kg and 20 kg. The exact mass will vary depending on the materials used.
Topic 1.1 · Physical quantities
Estimate the height of a typical classroom.
A reasonable estimate for the height of a typical classroom is between 3 meters and 4 meters. This can vary based on the type of building.
Topic 1.1 · Physical quantities
Estimate the time it takes for a car to accelerate from 0 to 60 mph (approximately 27 m/s) with typical acceleration.
Assuming typical acceleration, a car might take around 5 to 15 seconds to reach 60 mph. This is a broad estimate and depends heavily on the car's power.
Topic 1.2 · SI units
What is the SI unit of mass?
The SI unit of mass is the kilogram (kg). It is a base unit in the International System of Units and is used to measure the amount of matter in an object.
Topic 1.2 · SI units
What is the SI unit of time?
The SI unit of time is the second (s). It is a base unit in the International System of Units, defining the duration of events.
Review the material
Read full revision notes on Physical quantities — definitions, equations, common mistakes, and exam tips.
Read NotesMore topics in Unit 1 — Physical quantities and units
Physical quantities sits alongside these A-Level Physics decks in the same syllabus unit. Each uses the same spaced-repetition system, so progress in one informs the next.
Key terms covered in this Physical quantities deck
Every term below is defined in the flashcards above. Use the list as a quick recall test before your exam — if you can't define one of these in your own words, flip back to that card.
How to study this Physical quantities deck
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