Technologies K–10 · Years 9–10
Reaction times from a falling ruler: validating and analysing a class data set
Computing Technology 7–10 (NSW, 2022); Digital Technologies: Processes and production skills, Acquiring, managing and analysing data (ACARA v9)
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The idea
A falling-ruler test turns a catch distance into a reaction time, and a class data set needs validation rules and an outlier check before its trends are trusted.
What you need
- 30 cm ruler per pair
- Spreadsheet with a shared form or sheet for class data entry
How to do it
- The dropper holds the ruler with 0 cm between the catcher's open finger and thumb and releases it without warning; the catcher reads the distance at the top of the thumb.
- Record 20 catches per learner with each hand; record a miss as 'more than 30 cm', not as 30 cm and not left blank.
- In the spreadsheet, set validation: distance must be a number from 0 to 30 cm or the entry 'more than 30 cm'; flag anything else.
- Convert each distance to a time with t = √(2d ÷ g), g = 9.80 m/s².
- Find each learner's median and the class quartiles, placing each miss above every caught value; flag values above Q3 + 1.5 × IQR or below Q1 − 1.5 × IQR.
- Build an interactive chart (filter by hand and by trial number) and describe any trend with evidence.
What you should see
Catch distances convert to times of 0.101 s at 5 cm, 0.143 s at 10 cm, 0.175 s at 15 cm, 0.202 s at 20 cm, 0.226 s at 25 cm and 0.247 s at 30 cm, the longest time a 30 cm ruler can measure. Entries outside 0 to 30 cm are flagged by validation; a miss is kept as 'more than 30 cm' (slower than 0.247 s), because leaving it out would drop the slowest reactions and bias the data towards short times, and entering 30 cm would understate it. Medians and quartiles still hold with misses in the data, because a miss only has to sit above every caught value: a learner's median needs fewer than half of their trials to be misses, and the upper quartile fewer than a quarter. Values beyond the 1.5 × IQR fences are flagged as outliers and checked against notes (for example a distracted trial). The learner knows it worked when the conversions match these values and every flagged value has a stated reason.
What changes
- What you change
- hand used and trial number
- What you measure
- reaction time (s)
- What you keep the same
- the same ruler
- the same dropper
- release without warning
Common misconceptions
Each of these ideas is wrong, and the activity is a chance to test it.
- A longer catch distance means a faster reaction (it means a slower one).
- Outliers should be deleted (they are flagged and checked; some are real).
- One trial measures a person's reaction time (variation needs many trials and a median).
Safety card
Hazards
- Ruler edge hitting fingers
Controls
- Drop from just above the open hand
Note
No chemicals or heat.
Curriculum references
The NSW syllabus outcomes and Australian Curriculum v9 codes this activity supports. They are references, not a verified or complete curriculum alignment.
- Computing Technology 7–10 Syllabus (2022), NESA. Current elective syllabus. Code read from the outcomes page on 2026-09-22.CT5-DAT-02
- Australian Curriculum v9AC9TDI10P02AC9TDI10P01
Sources
The pages the author read to write this activity.
- curriculum.nsw.edu.au/learning-areas/tas/computing-technology-7-10-2022/outcomes
- education.nsw.gov.au/teaching-and-learning/curriculum/mathematics/mathematics-curriculum-resources-k-12/thinking-mathematically-resources/mathematics-s3-reaction-time-test
- www.digitaltechnologieshub.edu.au/plan-and-prepare/scope-and-sequence-f-10/years-9-10