MYP Physics: Measurement & Units — FAQ

Measurement and units is the MYP Physics topic covering the SI system (seven base units like kilogram, metre, second), derived units (newton, joule, pascal), significant figures, and uncertainty in measured quantities. It underpins every practical you'll run in MYP 4-5 and feeds directly into DP Physics's Tools and Inquiry Process skills.

The seven SI base units are the metre (length), kilogram (mass), second (time), ampere (current), kelvin (temperature), mole (amount of substance), and candela (luminous intensity). MYP Physics mainly uses the first five. Every derived unit — newton, joule, watt, pascal — breaks down into combinations of these.

Accuracy means how close a measurement is to the true value; precision means how consistent repeated measurements are with each other. You can be precise but inaccurate — five readings clustered tightly around the wrong number, say, because of a badly calibrated instrument. Examiners look for both terms used correctly, not interchangeably.

Count non-zero digits from the first non-zero digit; trailing zeros after a decimal point count too. Your final answer should carry the same number of significant figures as the least precise measurement used in the calculation — usually 2 or 3 sig figs for MYP-level data. Never round mid-calculation, only at the end.

For a single reading, uncertainty is usually half the smallest division on your instrument — a ruler marked in mm gives ±0.5 mm. For repeated readings, uncertainty is roughly half the range (highest minus lowest, divided by two). MYP assessments usually expect you to state this alongside your recorded value.

Most lost marks come from converting between prefixes incorrectly — mixing up centi-, milli- and kilo- — or forgetting to convert before substituting into a formula. A speed calculated in km/h left un-converted to m/s in a force equation will produce an answer that's wrong by a factor of thousands.

Top marks require correct units on every value, appropriate significant figures throughout, and a stated, justified uncertainty for any measured quantity — not just calculated ones. Criterion B's highest band explicitly asks for a scientifically justified explanation of precision and limitations, so name your instrument's resolution, don't just guess a number.

The three biggest: leaving units off a final answer entirely, inconsistent sig figs (mixing 2 and 4 sig figs across one calculation), and confusing uncertainty with percentage error. Examiners moderating Criterion B work flag missing units as the single most common and most avoidable deduction.

Quite a lot. The DP Physics guide, with first exams 2025, builds directly on these skills through the Tools programme — uncertainty propagation, error bars on graphs, and sig fig discipline are assessed every year in Paper 3 and the internal assessment. Students who skip this in MYP struggle noticeably at DP level.

Measurement and units are primarily assessed through Criterion A (Knowing and Understanding) for terminology and unit knowledge, and Criterion B (Inquiring and Designing) plus Criterion C (Processing and Evaluating) when you're running and analysing your own practical investigations, including justifying precision and identifying limitations.

No — related but not identical. MYP treats uncertainty fairly simply (half the smallest division, half the range). DP Physics requires propagating uncertainties through calculations, expressing them as percentages, and plotting error bars with a max/min gradient on graphs. MYP is the foundation; DP adds the mathematical rigour.

The most useful thing you can do is ask your child to explain why they chose a particular number of significant figures or unit in their homework — talking it through out loud usually reveals the gap faster than re-reading notes. Beyond that, a structured resource with worked examples helps far more than generic revision guides at this level.