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Science and Technology K–6 · Year 5

Stretch and roll: how a stronger push sends a car farther

Physical sciences (NSW 2017 Stage 3 Physical World, forces); Science inquiry (Australian Curriculum v9 Year 5)

Practical, model not builtLow risk

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The idea

A stronger applied force, here a rubber band stretched further, transfers more energy to a toy car, so it rolls farther before friction stops it; for a band that stretches evenly, doubling the stretch roughly quadruples the distance.

What you need

  • a toy car of about 100 g, weighed on a kitchen balance
  • a long rubber band (about 15 cm as an unstretched loop) held between two heavy chair legs 20 cm apart
  • a spring balance, 0 to 10 N
  • a 30 cm ruler taped to the floor behind the band to read the stretch
  • a 10 m tape measure and masking tape for the release line
  • a smooth, level floor at least 8 m long (a hall or corridor)
  • safety glasses

How to do it

  1. Hook the spring balance to the middle of the band and pull it back 2, 4, 6, 8 and 10 cm. Record the force at each stretch.
  2. Put the car's back against the band at the release line, pull the band and car back 2 cm and let go. Measure the distance from the release line to where the car stops.
  3. Do three runs at each stretch of 2, 4, 6, 8 and 10 cm and work out the mean distance.
  4. Graph mean distance against stretch. Then graph mean distance against stored energy, worked out as half x force x stretch (in newtons and metres) for each stretch.
  5. Use the graph to predict the distance for a 12 cm stretch, then test the prediction.
  6. Explain what the stronger pull changed and what finally stopped the car.

What you should see

The distance climbs steeply with stretch. For a band pulling 1.0 N at 5 cm (stiffness 20 N/m), the energy stored is 0.025 J at 5 cm and 0.100 J at 10 cm; with a 100 g car and a rolling-friction coefficient of 0.03 the model's upper limit is 0.85 m at 5 cm and 3.40 m at 10 cm, four times as far for twice the stretch, with launch speeds of 0.71 and 1.41 m/s. Real runs fall short of these limits because some energy stays in the band and goes into the car's wobble and wheels, but if the fraction passed on stays about the same, the graph of distance against stored energy comes out close to a straight line. The spring-balance readings check the band: if the force doubles when the stretch doubles, it stretched evenly.

What changes

What you change
stretch of the band (strength of the applied force)
What you measure
distance the car rolls
What you keep the same
  • same car and band
  • same floor
  • same release line and release method
  • three runs per stretch

Common misconceptions

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

  • Doubling the stretch doubles the distance.
  • The car stops because the push runs out (friction stops it; the push ended at the release line).
  • A heavier car always goes farther because it has more force.

Safety card

Low riskLearners carry it out

Hazards

  • a snapping rubber band can hit an eye
  • a rolling car underfoot
  • latex allergy (rubber bands are natural rubber latex)

Controls

  • safety glasses for the launcher and the measurer
  • launch only along the floor, away from people
  • replace any band that shows cracks
  • check allergy records; use a latex-free band if a learner has a latex allergy

Note

Risk assessment before the lesson using Primary RiskAssess or the school's own template.

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), current, taught until 2026; code read from the syllabus document on 22 September 2026ST3-9PW-STST3-1WS-S
  • Science and Technology K-6 Syllabus (2024), implemented from 2027; NESA's timeline is 2026 plan and prepare and 2027 start teaching, and schools may choose to implement it during 2026; code read from the outcomes page on 22 September 2026ST3-PQU-01ST3-DAT-01
  • Australian Curriculum v9AC9S5I01AC9S5I02AC9S5I04

Sources

The pages the author read to write this activity.

  1. www.scootle.edu.au/ec/search?accContentId=AC9S5I02
  2. www.nsw.gov.au/education-and-training/nesa/curriculum/science/science-and-technology-k-6-2017
  3. curriculum.nsw.edu.au/learning-areas/science/science-and-technology-k-6-2024/outcomes
  4. primaryconnections.org.au/v84-sequences/smooth-moves
  5. www.questacon.edu.au/learn-and-play/activities/catapults

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