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Technologies K–10 · Years 5–6

Gear trains: counting turns to change speed and direction

Physical World (NSW Science and Technology K–6, 2017), design and production outcome only: neither NSW K–6 syllabus has a content point on gears; Design and Technologies: Knowledge and understanding, Technologies context: Materials and technologies specialisations (ACARA v9)

Practical, model not builtLow risk

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The idea

When two gears mesh, the same number of teeth pass each other, so a small gear turning a gear with 5 times as many teeth turns it 5 times more slowly, in the opposite direction, and with more turning force.

What you need

  • 1 plastic gear set with a pegboard: two 8-tooth gears, one 16-tooth gear, one 24-tooth gear and two 40-tooth gears, with a way to fix an 8-tooth gear to a 40-tooth gear so they turn together on one axle
  • 1 crank handle
  • Small paper flags taped to each gear
  • Counting sheet

How to do it

  1. Mesh an 8-tooth gear (the driver) with a 40-tooth gear. Tape a flag on each.
  2. Turn the driver 10 full turns and count the turns of the 40-tooth gear. Note the directions.
  3. Swap them so the 40-tooth gear drives the 8-tooth gear. Turn the driver 2 turns and count.
  4. Put a 16-tooth gear between the 8 and the 40 (an idler). Count turns and note directions again.
  5. Build a compound train: 8 drives 40; an 8-tooth gear on the same axle as that 40 drives a second 40. Turn the first gear 10 turns and count the last gear's turns.
  6. Design a gear train that makes an output turn 3 times for each input turn, then test it.

What you should see

8 driving 40: 10 input turns give 2.0 output turns (a ratio of 5 to 1) in the opposite direction. 40 driving 8: 2 input turns give 10 output turns. The idler, whatever its size, makes the output turn the same way as the input and keeps the ratio at 5 to 1. The compound train has a ratio of 25 to 1, so 10 input turns give 0.4 of a turn. A 24-tooth gear driving an 8-tooth gear gives the 3-times-faster output. Ignoring friction, the turning force rises by the same factor that the speed falls. The learner knows it worked when counted turns match the ratio of teeth.

What changes

This activity lists no variables to change, measure and keep the same.

Common misconceptions

Each of these ideas is wrong, and the activity is a chance to test it.

  • A bigger gear always turns faster (a bigger driven gear turns more slowly).
  • The idler gear changes the speed (it changes only the direction).
  • Gears create energy (they trade speed for turning force; friction wastes a little).

Safety card

Low riskLearners carry it out

Hazards

  • Pinched fingers between gear teeth

Controls

  • Turn by the crank handle, not by the teeth

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.

  • Science and Technology K–6 Syllabus (2017), NESA. The syllabus taught in 2026; the 2024 syllabus replaces it from 2027. Code read from the official syllabus document (DOCX) on 2026-09-22.ST3-2DP-T
  • Science and Technology K–6 Syllabus (2024), NESA. Implementation from 2027, so this code describes the future syllabus. Code read from the outcomes page on 2026-09-22.ST3-DDT-01
  • Australian Curriculum v9AC9TDE6K05AC9TDE6P02AC9TDE6P03

Sources

The pages the author read to write this activity.

  1. www.nsw.gov.au/education-and-training/nesa/curriculum/science/science-and-technology-k-6-2017
  2. curriculum.nsw.edu.au/learning-areas/science/science-and-technology-k-6-2024/outcomes
  3. www.teachengineering.org/activities/view/nyu_gears_activity1
  4. www.teachengineering.org/lessons/view/umo_challenges_lesson02

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