Physics · Unit 9

Measurement and Units

Measuring the physical world

Physics is a quantitative subject, so a result without a unit and an uncertainty is not a result.

The unit covers SI units and why a shared system mattered, measuring length, mass and time, accuracy, precision and error, and reading data off a graph.

This unit breaks down into 20 short steps and 119 questions, starting at difficulty 2 and building to 3. Below you can see exactly what it covers, how the path is structured, and worked examples with explanations.

Steps: 20
Questions: 119
Difficulty: 2-3

What this unit covers

SI Units
Accuracy, Precision and Error
Measuring Tools
Graphs and Data
Length, Mass and Time

Where this fits

Underpins every practical unit in the track.

Where people slip

Every measurement has an uncertainty. A reading given as exactly 3 metres is claiming something no instrument can support, and treating it as exact propagates a false confidence.

How the unit is structured

Measurement and Units runs as 20 short steps that unlock in order. 15 are practice rounds and 5 are challenge rounds that pull together everything before them. Questions start at difficulty 2 and climb to 3 as you progress.

Step 1 · easierStep 20 · harder

Challenge rounds

Example questions

30 real questions from this unit, with the answer and the reason behind it, grouped by what they practise. There are 119 in the unit altogether.

Accuracy, Precision and Error

Choose all that applyLevel 2
1. Which actions help reduce random error in an experiment?
- Repeat the measurement several timescorrect
- Take an average of the readingscorrect
- Always read the scale from an angle
- Use an instrument with a zero error
Repeating measurements and averaging the readings both reduce the effect of random error.
Fact or fibLevel 2
2. A measurement that is very precise must also be accurate.
Answer: False
False: readings can be precise (close to each other) yet all wrong because of a systematic error, so precise does not mean accurate.
Fill the blankLevel 2
3. A ____ error shifts every reading by the same amount in the same direction.
- systematiccorrect
- random
- reading
- rounding
A systematic error, such as a zero error, biases all readings the same way and cannot be reduced by averaging.
Multiple choiceLevel 2
4. Accuracy describes how close a measurement is to what?
- The true valuecorrect
- The other readings only
- Zero
- The largest reading
Accuracy is how close a measured value is to the true or accepted value.
Odd one outLevel 2
5. Which of these is NOT a cause of random error?
- A zero error on the instrumentcorrect
- Human reaction time
- Parallax when reading a scale
- Small changes in the surroundings
A zero error is a systematic error that biases every reading, unlike reaction time, parallax, or changing surroundings which vary randomly.
Guess the numberLevel 3
6. A length is measured as 50 mm with an absolute uncertainty of 1 mm. What is the percentage uncertainty?
Answer: 2 %
Percentage uncertainty is (1 / 50) x 100, which equals 2 percent.

Graphs and Data

Build the sentenceLevel 2
7. Build the sentence that defines the gradient of a straight-line graph.
Answer: the gradient equals rise over run
The gradient equals the rise divided by the run, that is the vertical change over the horizontal change.
Choose all that applyLevel 2
8. Which are good practices when drawing a line graph?
- Label each axis with its unitcorrect
- Draw a smooth line of best fitcorrect
- Join points with jagged zig-zag lines
- Leave the axes unlabelled
A good graph has clearly labelled axes with units and a smooth line of best fit rather than jagged point-to-point lines.
Fill the blankLevel 2
9. On a distance-time graph, the gradient of the line represents the ____.
- speedcorrect
- mass
- time
- area
The gradient of a distance-time graph is distance divided by time, which equals the speed.
Guess the numberLevel 2
10. A distance-time graph line rises 10 m over a time of 2 s. What speed does its gradient give, in m/s?
Answer: 5 m/s
Gradient equals distance divided by time, so 10 m divided by 2 s gives a speed of 5 m/s.
Multiple choiceLevel 2
11. On a graph, the independent variable is usually plotted on which axis?
- The horizontal x-axiscorrect
- The vertical y-axis
- The diagonal axis
- It is never plotted
The independent variable (the one you change) goes on the horizontal x-axis, and the dependent variable goes on the y-axis.
Match the pairsLevel 3
12. Match each graph feature to the physical quantity it represents.
Answer: Gradient of a distance-time graph = Speed; Gradient of a velocity-time graph = Acceleration; Area under a velocity-time graph = Displacement; Area under a force-extension graph = Work done
A distance-time gradient gives speed, a velocity-time gradient gives acceleration, the area under a velocity-time graph gives displacement, and the area under a force-extension graph gives work done.

Length, Mass and Time

Build the sentenceLevel 2
13. Build the sentence about how mass is measured.
Answer: mass is measured in kilograms
Mass is measured in kilograms, the SI base unit for mass.
Fact or fibLevel 2
14. There are 1000 grams in one kilogram.
Answer: True
Correct: the prefix kilo means one thousand, so one kilogram equals 1000 grams.
Fill the blankLevel 2
15. One centimetre equals ____ millimetres.
- 10correct
- 100
- 5
- 1000
One centimetre is 10 millimetres, since there are 1000 millimetres in a metre and 100 centimetres in a metre.
Guess the numberLevel 2
16. How many metres are there in one kilometre?
Answer: 1000 m
The prefix kilo means one thousand, so one kilometre equals 1000 metres.
Choose all that applyLevel 3
17. Which of these quantities share the same dimensions as energy (M L^2 T^-2)?
- Torquecorrect
- Workcorrect
- Heatcorrect
- Power
- Pressure
Torque, work and heat all reduce to M L^2 T^-2; power is energy per time and pressure is force per area, so they differ.
Match the pairsLevel 3
18. Match each SI prefix to the power of ten it represents.
Answer: nano = 10^-9; micro = 10^-6; kilo = 10^3; giga = 10^9
Nano is 10^-9, micro is 10^-6, kilo is 10^3 and giga is 10^9.

Measuring Tools

Guess the numberLevel 2
19. A typical micrometer screw gauge can read down to about what smallest length, in millimetres?
Answer: 0.01 mm
A standard micrometer reads to about 0.01 mm, far finer than a ruler's 1 mm divisions.
Match the pairsLevel 2
20. Match each measuring tool to the quantity it measures.
Answer: Ruler = Length; Balance = Mass; Stopwatch = Time; Thermometer = Temperature
A ruler measures length, a balance measures mass, a stopwatch measures time, and a thermometer measures temperature.
Multiple choiceLevel 2
21. Which tool is best for measuring the tiny diameter of a wire?
- Micrometercorrect
- Metre ruler
- Measuring cylinder
- Stopwatch
A micrometer screw gauge can measure very small thicknesses, reading to about 0.01 mm.
Picture questionLevel 2
22. 📏 Which quantity is this instrument used to measure?
- Lengthcorrect
- Mass
- Time
- Temperature
A ruler is a tool for measuring length or distance.
Fill the blankLevel 3
23. An instrument that reads a value other than zero when the true value is zero has a ____ error.
- zerocorrect
- random
- parallax
- reading
A zero error is a systematic fault that must be subtracted from every reading the instrument gives.
Odd one outLevel 3
24. Three of these instruments measure length. Which is the odd one out?
- Thermometercorrect
- Metre rule
- Vernier caliper
- Micrometer
A thermometer measures temperature, while a metre rule, vernier caliper and micrometer all measure length.

SI Units

Fill the blankLevel 2
25. The SI base unit of temperature is the ____.
- kelvincorrect
- celsius
- fahrenheit
- joule
The kelvin is the SI base unit of temperature; 0 kelvin is absolute zero.
Guess the numberLevel 2
26. How many base units are there in the SI system?
Answer: 7 base units
The SI system has 7 base units: metre, kilogram, second, ampere, kelvin, mole, and candela.
Match the pairsLevel 2
27. Match each quantity to its SI base unit.
Answer: Length = Metre; Mass = Kilogram; Time = Second; Temperature = Kelvin
Each SI base quantity has one base unit: length uses the metre, mass the kilogram, time the second, and temperature the kelvin.
Multiple choiceLevel 2
28. What is the SI base unit of length?
- Metrecorrect
- Litre
- Gram
- Newton
The metre is the SI base unit of length; other length units like the kilometre are built from it.
Odd one outLevel 2
29. Which of these is NOT an SI base unit?
- Newtoncorrect
- Metre
- Second
- Kelvin
The newton is a derived unit (kg m/s^2), while the metre, second, and kelvin are true SI base units.
Choose all that applyLevel 3
30. Which of these are SI base units? (Select all that apply.)
- Amperecorrect
- Molecorrect
- Coulomb
- Pascal
The ampere and the mole are SI base units, while the coulomb and the pascal are derived units.

Where these questions come from. Each unit starts as a plan of the concepts it should cover and the difficulty it should span. Questions are written against that plan with AI assistance, then checked by a validator that rejects anything without a single defensible answer, an explanation, or plausible wrong options. How we write questions sets out the whole process, and corrections are fixed in the bank and reach the site and the app the same day.

How you practise

This unit mixes 16 different question formats, so you are recalling and applying rather than recognising the same layout every time.

Build the sentence
Choose all that apply
Fact or fib
Fill the blank
Guess the number
Listen and choose
Match the pairs
Multiple choice
Odd one out
Picture question
Put in order
Sort into groups
Spell it
Tap the pairs
True or false
Type the answer

Practise Measurement and Units

119 questions across 20 steps. Start with step one and crawl at your own pace.

Play this unit

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