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Technologies K–10 · Years 7–8

Rubber-band racers: stored energy, wheel size and distance

Engineering Technologies and Systems focus area (NSW Technology 7–8, 2023); Design and Technologies: Knowledge and understanding, Technologies context: Engineering principles and systems (ACARA v9)

Practical, model not builtMedium risk

School laboratory, not for home

In a school laboratory, with a teacher supervising, under the school's risk assessment. Not for home.

This site has no interactive model of its own. Where a step or a material names a Concept Studio model, simulation or tool, it has not been built; an external simulation a step names (for example PhET) is not part of this site.

The idea

A wound rubber band stores elastic energy that the axle turns into motion, and each axle turn moves the racer one wheel circumference, so wheel size, winding and friction decide how far it goes.

Safety card

Medium riskA teacher supervises

Setting: In a school laboratory, with a teacher supervising, under the school's risk assessment. Not for home.

Hazards

  • Saw and drill injuries
  • Glue gun burns
  • Rubber bands snapping into eyes

Controls

  • Teacher demonstration and supervision of saws and drills; work held in a vice
  • Low-temperature glue gun on a stand; cool water nearby for burns
  • Safety glasses when winding and testing

Note

Follow NSW Department of Education TAS compliance advice (mandated controls and Equipment Safety in Schools), education.nsw.gov.au/teaching-and-learning/curriculum/tas/tas-compliance; record the activity on RiskAssess (riskassess.com.au).

What you need

  • Chassis material (pine, MDF or corflute) cut to less than 250 mm long and 10 to 120 mm wide, as set in the NESA sample unit
  • Wheels no larger than 150 mm diameter that were not made as wheels (for example old 120 mm compact discs or jar lids)
  • 6 mm dowel axles, drinking straws as bearings, rubber bands
  • Coping saw, hand drill, low-temperature glue gun; safety glasses
  • Slotted masses (10 × 100 g) and a ruler to measure how far a band stretches; 10 m tape measure; timer

How to do it

  1. Test the rubber band: hang 100 g masses one at a time up to 1 kg and measure the stretch; graph force against stretch and find its slope (the stiffness k).
  2. Design the racer within the size limits and draw it with dimensions; plan the build as a timeline and a cost list of materials.
  3. Build the chassis, fit the axles through straw bearings, and attach the band so it winds around the drive axle.
  4. Wind the axle 10 turns, release on a level floor and measure the distance. Repeat 3 times.
  5. Predict the powered distance from the wheel circumference and the number of turns, then compare.
  6. Change one feature (wheel diameter, number of turns, mass) and test again; evaluate the design against criteria agreed by the class, including the environmental impact of the materials used.

What you should see

A 120 mm disc wheel (the ECMA-130 disc diameter) rolls 0.377 m per turn, so 10 axle turns power the racer for up to 3.77 m if the wheels do not slip; the racer travels further only if it keeps coasting after the band lets go, and less if the wheels spin. Each turn winds about 18.8 mm of band onto the 6 mm axle, so 10 turns stretch the band by about 0.19 m; the learner checks that this stretch lies inside the range of their hanging-mass graph before using the graph for the stored energy. A rubber band's force–stretch graph is not a perfect straight line, so the learner fits the straight middle part to estimate k, or finds the stored energy as the area under the graph. The lightest racer is not always the one that travels furthest, a question the NESA sample unit asks learners to test. The learner knows it worked when measured distances are consistent across 3 trials and they can explain any gap from the predicted powered distance (slip, friction, coasting).

What changes

What you change
one design feature (wheel diameter, number of turns or mass)
What you measure
distance travelled (m)
What you keep the same
  • the same rubber band
  • the same floor surface
  • release without a push
  • 3 trials each

Common misconceptions

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

  • The fastest racer goes furthest (speed and distance depend on different features).
  • Bigger wheels always go further (they cover more ground per turn but need more force to turn).
  • The band gives out energy it did not get (every joule stored came from the work of winding).

Curriculum references

The NSW syllabus outcomes and Australian Curriculum v9 codes this activity supports. They are references, not a verified or complete curriculum alignment.

  • Technology 7–8 Syllabus (2023), NESA. Current: taught from 2026. Code read from the outcomes page on 2026-09-22.TE4-MSC-01TE4-PPM-01TE4-SAF-01
  • Technology Mandatory 7–8 Syllabus (2017), NESA. Outgoing: replaced by the Technology 7–8 Syllabus (2023) from 2026 and not available after December 2027. Code read from the official syllabus document (DOCX) on 2026-09-22.TE4-8ENTE4-1DPTE4-2DPTE4-3DP
  • Australian Curriculum v9AC9TDE8K03AC9TDE8P02AC9TDE8P03AC9TDE8P04AC9TDE8P05

Sources

The pages the author read to write this activity.

  1. curriculum.nsw.edu.au/learning-areas/tas/technology-7-8-2023/outcomes
  2. www.nsw.gov.au/education-and-training/nesa/curriculum/tas/technology-mandatory-7-8-2017
  3. www.nsw.gov.au/sites/default/files/noindex/2024-11/technology-mandatory-years-7-8-sample-unit-engineered-systems-rb-racers.docx
  4. ecma-international.org/publications-and-standards/standards/ecma-130
  5. education.nsw.gov.au/teaching-and-learning/curriculum/tas/planning-programming-and-assessing-tas-7-10/technology-7-8

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