SI Units

  • SI units and prefixes
  • the estimation of physical quantities
  • the limitations of physical measurements
  • estimating uncertainty

A secure understanding of these fundamental concepts which underpin the whole of physics is crucial for all students. They need to be able to look at an answer and know if the answer is too big, too small or just about right. This is a concept that a lot of students struggle with. Start by teaching the prefixes required, and the sizes that these relate to, before introducing the SI units. It is useful for students to be able to derive these. Estimation and limitations complete the sequence.

Students should be familiar with orders of ten and SI units from their work at GCSE. They may not have come across uncertainty or deriving SI units previously.

Whilst this list provides a source of information and ideas for experimental work, it is important to note that recommendations can date very quickly. Do NOT follow suggestions which conflict with current advice from CLEAPSS or recent safety guides. eLibrary users are responsible for ensuring that any activity, including practical work, which they carry out is consistent with current regulations related to Health and Safety and that they carry an appropriate risk assessment. Further information is provided in our Health and Safety guidance.

Links and Resources

Estimating Length Using Standard Form

These materials are designed to raise awareness of the importance of estimating and to practise the skill. It would make a good introductory lesson to the course, or could be used as part of a bridging unit between GCSE and A level courses.

The activity includes discussion and matching sets of measurement cards to cards describing an object, as well as a lesson plan suggesting how these activities are best used, which will be useful to a teacher new to A level physics.

The measurement matching cards consist of a picture, a measurement and a measurement in standard form. This would be good completed by students in pairs to enable discussion while they are working, and then encourage each pair to compare with another in the class to ensure they all agree before running through the answers with them. It will also enable you to pick up and deal with any misconceptions early on in the topic.


publication year
2000 - 2009

4 files



Errors *suitable for home teaching*

The Nuffield Foundation provides this activity which helps students understand how big errors may be, and how errors accumulate when measurements are used in calculations. This is particularly important in scientific contexts.

There are a series of worked examples on the activity sheet, followed by practice questions for students to complete. This would make a good homework task, but could equally be used in class to test understanding and knowledge.


publication year
2010 to 2019

3 files



Measurement Good Practice Guide: a Beginner's Guide to Uncertainty of Measurement *suitable for home teaching*

This publication from the National Physical Laboratory is an ideal resource for secondary teachers but could also be used by students at post-16 level. It can be used as a basis for best practice for taking measurements within the laboratory.

The guide explains the basics of errors, uncertainties, spread, standard deviation, random and systematic error, sources of error and uncertainty, reducing uncertainty and combining uncertainties. There is also a useful appendix on understanding the terminology.

There is a lot of reading, so this again is possibly best set as homework, or used to support lesson planning.

publication year
2000 - 2009

1 file



Symbols and Units: a Survival Guide *suitable for home teaching*

  • the guide contains six sections:
  • SI base units
  • derived units
  • secondary units and prefixes
  • units outside the SI
  • using SI units and their symbols
  • some useful physical constants

Although this is a resource developed by SAPS, the content is entirely relevant to the physics course and is an ideal starting point for either use in class, home learning or as a reference material throughout the course.

It would be useful to provide each student with a copy of this, particularly sections one, two and three. 

As an introduction to the course these could be provided with gaps missing to see what knowledge students already have or can derive.

publication year
2000 - 2009

1 file



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