Measuring accurately and judging whether to trust it
Anyone can write a number down. The skill is choosing the right instrument, reading it properly, and then being honest about how much your method can actually be trusted.
Part of your national curriculum
- Working scientifically: Make and record observations and measurements using a range of methods, and evaluate the reliability of methods
Lesson overview
What you'll learn in this lesson
Make and record observations and measurements using a range of methods, and evaluate the reliability of methods
Key learning points
- • Choosing the instrument
- • Recording as you go
- • Judging reliability
- • Improving it
This lesson at a glance
- 30 minutes
- 19 parts to scroll through
- 4 quick checks
- Marked quiz at the end
- Gentle pace: short sittings with pauses
Words to know
Scroll down — the lesson carries on below
Watch & discover
Part 1 of 19
Watch first
Measuring accurately and judging whether to trust it
An English teaching video on this topic from Miacademy & MiaPrep Learning Channel. Watch it, then scroll down for the lesson.
Do it for real
The practicals below use what the film shows, with a full method you can follow at home.
In a nutshell
Make and record observations and measurements using a range of methods, and evaluate the reliability of methods
What you already know
Part 2 of 19
Before we start
What you already know
You should be able to identify independent, dependent and control variables in a fair test.
Key words
Part 3 of 19
Key words
Words you'll need today
- Resolution
- The smallest change an instrument can show.
- Repeatable
- You get similar results when you repeat the method yourself.
- Reproducible
- Someone else gets similar results with their own equipment.
- Anomaly
- A reading that does not fit the pattern of the others.
- Mean
- The average of repeated readings, after excluding anomalies.
Learning cycle
Part 4 of 19
Learning cycle 1 of 2
Taking measurements well
A short piece of teaching, then a check to make sure it has landed.
Explore the idea
Part 5 of 19
Learn
Choosing the instrument
Match the instrument to the size of the thing and to the precision you need. A ruler with millimetre marks has a resolution of 1 mm; a stopwatch reading hundredths is precise but your reaction time is roughly 0.2 s, so timing a single swing of a pendulum is pointless - time ten swings and divide. Measuring cylinders are read at eye level from the bottom of the meniscus, or the parallax error is bigger than the quantity you are arguing about.
Explore the idea
Part 6 of 19
Learn
Recording as you go
Write readings straight into a prepared table, in the units and to the resolution of the instrument, and never onto scrap paper 'to copy up later'. Repeat each reading at least three times, look for anomalies, exclude them from the mean and say why you excluded them. Repeats also tell you something the single reading cannot: how much your measurements scatter.
Quick check
Part 7 of 19
Quick check
The resolution of a millimetre ruler is...
Quick check
Part 8 of 19
Quick check
Why time ten pendulum swings rather than one?
Reset break
Part 9 of 19
Pause
That's sitting 1 of 2 done
Stretch, get a drink, look out of the window. There is no timer and nothing is counting down — your place is saved, so you can come back in five minutes or tomorrow.
Learning cycle
Part 10 of 19
Learning cycle 2 of 2
Evaluating the method
A short piece of teaching, then a check to make sure it has landed.
Explore the idea
Part 11 of 19
Learn
Judging reliability
Close repeats suggest the method is repeatable; wide scatter suggests something is not controlled. A method can be beautifully repeatable and still wrong - a scale that reads 5 g too high every time gives consistent, consistently wrong readings. So check zeroes, and where possible check against a known value or another method.
Explore the idea
Part 12 of 19
Learn
Improving it
An honest evaluation names what limited the accuracy and says what you would change: a data logger instead of a stopwatch, insulation to stop heat leaking, a wider range of values, more repeats, a light gate instead of hand timing. That is far more useful than 'I would be more careful'. If another class got a different answer with different equipment, your result is not yet reproducible - and that matters more than a neat graph.
Quick check
Part 13 of 19
Quick check
A balance that always reads 5 g high shows...
Quick check
Part 14 of 19
Quick check
Results are reproducible when...
Common mix-ups
Part 15 of 19
Common mix-ups
Things people often get wrong
- Precise is not the same as accurate - a wrong instrument can be very precise.
- Anomalies are excluded from the mean, not silently deleted from the table.
- Repeatable means you get the same result; reproducible means others do too.
- More repeats reduce the effect of random error but not a systematic zero error.
Challenge round
Part 16 of 19
Game · Sort it
Which of these are true?
Drag each card into the right column. Tap a card first if dragging is fiddly.
True
Not true
Challenge round
Part 17 of 19
Game · Fill the gaps
Finish the sentences
Choose the word that belongs in each gap.
Repeats also tell you something the single reading cannot: how much your ____ scatter.
Mastery quiz
Part 18 of 19
Marked quiz
End of lesson quiz: Measuring accurately and judging whether to trust it
6 questions, marked with the reasoning shown. No timer.
1. A liquid volume should be read...
2. An anomalous result should be...
3. Repeating readings mainly reduces...
4. Which improvement is a real one?
5. Wide scatter across repeats suggests...
6. Precise but inaccurate means readings are...
Lesson round-up
Part 19 of 19
Lesson round-up
Ready when you are
Quiz score
Not sat
Games
Not played
Points this lesson
0
Best run
0 in a row
Luna: 0 out of 4 on the practice checks. Only if you feel up to it — one more?
Ask LunaDo the work
Your written work for this lesson
This is the part you'd do in your book at school. Pick the pieces below, write here or on paper, and photograph anything you draw or work out.
Why the school greenhouse failed
A science club grew tomato plants in the school greenhouse. In June the plants grew well: leaves were dark green and the fruit set quickly. In July the club went away for two weeks and left the greenhouse door shut. When they came back, the leaves were curled and pale and most of the fruit had dropped.
The club had a data logger inside. It showed the temperature reached 46 °C on several afternoons and the soil moisture fell close to zero. The club knew photosynthesis needs light, water and carbon dioxide, and that enzymes in a plant work best in a narrow range of temperature. Above that range the enzymes stop working properly.
The club repeated the summer with the door propped open and a water bottle drip on each pot. Temperature peaked at 31 °C and the plants survived.
Written for Good Learning Co.
Reading questions
- Name the variable the club changed the second time, and one variable they kept the same.
- Explain, using the words photosynthesis and enzymes, why the plants were damaged in July.
- Write a conclusion for the club's report, saying how far the evidence supports it.
Method and results
WritingWrite the aim, what you changed, what you measured and what you kept the same, then record your results in a table.
1 page + results table
Conclusion
WritingExplain what your results show and why, using the scientific words from the lesson. Say how you know you can trust them.
6–8 sentences
Labelled diagram
DiagramDraw the apparatus or the process in pencil, label it fully, and photograph it.
1 labelled diagram
Reading and notes
ReadingRead the lesson text again and write the key ideas in your own words.
Half a page of notes
Saved as you type.
Part 1 of 19 · Watch & discover
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Make and record observations and measurements using a range of methods, and evaluate the reliability of methods