Slide 1 of 7 · Settling starter · Science · Year 8
5 minutesCalculating Means and Anomalies in an Insulation Investigation
When scientists repeat an experiment four times, one reading sometimes goes wrong because of a mistake in the method. Today you will spot an anomaly in a Year 8 thermal insulation practical, calculate means and percentage heat loss, and explain which material is the best insulator.
While the register is called: write your name, class and date on your worksheet, then read Sections 1 and 2 of the stimulus sheet and answer the starter question in rough.
Starter question: Look at the 4 repeat temperature drops for Bubble wrap (17.5°C, 18.5°C, 29.0°C, 18.0°C). Which reading does not fit the pattern, and what mistake in the lab notes caused it?
Slide 2 of 7 · Today’s brief and key words · Science · Year 8
5 minutesToday’s brief and key vocabulary
Class 8B at Ysgol Bryn Celyn poured 200 cm³ of hot water at 80.0°C into five beakers wrapped in different materials and measured the temperature drop over 15 minutes. You will process their raw data and write the conclusion.
Data and calculation
- Anomaly (outlier): a result that does not fit the pattern of the other repeats.
- Mean (average): sum of valid repeats ÷ number of valid repeats.
- Range: highest valid reading − lowest valid reading (shows spread).
Physics of heat transfer
- Thermal conductor: a material that lets heat energy pass through it quickly (such as metal).
- Thermal insulator: a material that slows down heat transfer, often by trapping pockets of air.
Slide 3 of 7 · Step 1: Variables and spotting the anomaly · Science · Year 8
10 minutesStep 1: Variables and why anomalies must be excluded
First identify the independent, dependent and control variables in Step 1(a). Then compare what happens to the Bubble wrap mean if you mistakenly include the 29.0°C anomaly versus excluding it.
Rule for anomalies when calculating a mean:
- Wrong way (including Repeat 3): (17.5 + 18.5 + 29.0 + 18.0) ÷ 4 = 83.0 ÷ 4 = 20.75°C (20.8°C to 1 d.p.).
- Correct way (excluding Repeat 3 and dividing by 3): (17.5 + 18.5 + 18.0) ÷ 3 = 54.0 ÷ 3 = 18.0°C.
Notice that when you cross out 1 anomaly from 4 repeats, you must divide the remaining sum by 3, not 4!
Slide 4 of 7 · Step 2 & Step 3: Means, ranges and percentage heat loss · Science · Year 8
10 minutesStep 2 and Step 3: Calculating means, ranges and percentage heat loss
Complete the results table in Step 2, then work out the final water temperature and percentage heat loss from the 80.0°C starting temperature in Step 3.
Worked example (Beaker A: No insulation control):
- Mean temperature drop: (32.5 + 31.5 + 32.0 + 32.0) ÷ 4 = 128.0 ÷ 4 = 32.0°C.
- Range of valid repeats: 32.5 − 31.5 = 1.0°C.
- Final temperature after 15 min: 80.0 − 32.0 = 48.0°C.
- Percentage heat loss from 80.0°C: (32.0 ÷ 80.0) × 100 = 40.0%.
Slide 5 of 7 · Step 4: Writing the scientific conclusion · Science · Year 8
12 minutesStep 4: Writing your structured conclusion
Use your completed tables in Steps 2 and 3 and the physics fact box in Section 4 of the stimulus sheet to write a 4-part conclusion.
Include these 4 parts in your Step 4 conclusion:
- Rank order: Rank the materials from best thermal insulator to worst, quoting their mean temperature drops (°C) and percentage heat losses (%).
- Best insulator explained: Explain why sheep’s wool fleece (12.0°C drop, 15.0% loss) and bubble wrap (18.0°C drop, 22.5% loss) performed best by linking trapped pockets of air to slow thermal conduction.
- Worst wrap explained: Explain why aluminium foil had a large drop (28.0°C, 35.0% loss) because metal is a good thermal conductor with no trapped air.
- Control & anomaly: State why Beaker A (unwrapped, 32.0°C) was needed and how excluding Repeat 3 fixed the Bubble wrap mean.
Slide 6 of 7 · Partner and self check · Science · Year 8
5 minutesCheck your calculations and conclusion against the success criteria
Check your own worksheet or swap with your partner. Tick each box in the success criteria table only when you have verified the working and units.
- Did you circle 29.0°C as the anomaly and calculate the Bubble wrap mean both ways (20.8°C with it vs 18.0°C without it)?
- Are all five means and ranges in Step 2 accurate to 1 decimal place?
- Are all five final temperatures and percentage heat losses in Step 3 correct?
- Does your Step 4 conclusion quote figures and explain how trapped air reduces thermal conduction?
Slide 7 of 7 · Plenary quick-check · Science · Year 8
3 minutesPlenary: Quick-check results table
Check your completed numbers against the master table below before handing in your worksheet.
| Beaker & material | Valid mean drop (°C) | Range (°C) | Final temp (°C) | Percentage heat loss (%) |
|---|---|---|---|---|
| A: No insulation (control) | 32.0 | 1.0 | 48.0 | 40.0% |
| B: Aluminium foil | 28.0 | 1.0 | 52.0 | 35.0% |
| C: Corrugated cardboard | 22.0 | 1.0 | 58.0 | 27.5% |
| D: Bubble wrap (excl. 29.0°C) | 18.0 | 1.0 | 62.0 | 22.5% |
| E: Sheep’s wool fleece | 12.0 | 1.0 | 68.0 | 15.0% |