Physics · Grades 5–8
Measurements, units and sensible precision
Read scales, record units and separate measurements from assumptions.
Learn the idea
Record a quantity
Write a numerical value and its unit. A bare number is often insufficient to identify a measurement.
Scale reading
Align the object with the scale zero, look squarely at the scale and consider its smallest division.
Precision
More written digits do not automatically mean a more accurate measurement. Report what the instrument can support.
Repeats
Repeated measurements reveal variation. A mean can reduce random variation but will not repair a consistent zero error.
Worked examples
Which record is most informative for a measured length?
It gives both value and unit.
12.4 cm
A length is 0.75 m. Express it in centimetres.
There are 100 cm in 1 m, so 0.75 × 100 = 75 cm.
75 cm
Check your understanding
Measurements are 18, 20 and 22 seconds. Find their mean.
A ruler starts its numbered scale 5 mm from its end. Where should the object start?
- Always at the physical end
- At any number without adjustment
- At the scale's zero mark
Why is writing 12.000000 cm from a coarse ruler misleading?
Answers and marking notes
Answers and marking notes
- 20 s
Their sum is 60 s; divide by 3.
- At the scale's zero mark
The measuring origin is the marked zero, not necessarily the ruler's edge.
- The digits suggest precision the instrument did not establish.
Credit a distinction between displayed digits and measurement resolution.
Further reading and review references
These are reference links, not copied exercises, institutional endorsement or proof of independent review.
Independent educational review required. Grade bands are approximate; these are not officially aligned curricula.