Science 7–10 · Year 8
Rubber-band car: elastic potential energy transformed into motion
Physical sciences — Change, content group Energy transfers (NSW Stage 4 focus area)
The idea
Energy stored in a stretched rubber band is transformed into kinetic energy of the car and then into thermal energy through friction, so more winding stores more energy and drives the car further.
What you need
- rubber-band car kit or: cardboard chassis, 4 bottle-top wheels, 2 wooden skewer axles, a drinking straw for axle bearings, 1 set
- rubber bands 90 mm x 1.5 mm, 5
- 50 g slotted mass to tape to the chassis for the design change, 1
- alternative larger wheels: jar lids about 70 mm across, 4
- paperclip hook, 1
- tape measure 5 m, 1
- stopwatch, 1
- smooth floor 5 m long
How to do it
- Build the car so one rubber band is anchored to the front of the chassis and hooked to the rear axle; winding the rear wheels backwards wraps the band around the axle.
- Wind the rear axle exactly 5 turns, place the car on the start line and release. Measure the distance travelled to the nearest centimetre. Three trials, average.
- Repeat for 10, 15 and 20 turns. Stop if the band is at full stretch.
- Plot distance against turns and describe the pattern; use the data to argue for or against the claim that doubling the turns doubles the distance, and identify where the stored energy has gone once the car stops.
- Time the car over the first 1.0 m for 10 and 20 turns to compare average speeds.
- Change one design feature (wheel size, adding a second band, adding a 50 g load) and test how distance changes.
What you should see
Distance travelled rises with the number of turns, and often more steeply than in proportion, because a rubber band stores more energy per turn as it stretches further. The wheels may spin on the spot for the first moment if the band releases too fast. Adding a 50 g load changes the run: with the same stored energy, a heavier car has larger friction forces at the axles and on the floor, so it usually travels less far unless the unloaded wheels were slipping. The learner knows it worked when the run distance rises in a repeatable pattern with turns.
What changes
- What you change
- number of turns wound onto the axle
- What you measure
- distance travelled (m)
- What you keep the same
- same car and band
- same floor and start line
- release without pushing
Common misconceptions
Each of these ideas is wrong, and the activity is a chance to test it.
- The car keeps moving until its energy is used up and then the energy is gone.
- Doubling the turns must exactly double the distance.
- A heavier car goes further because it has more momentum.
Safety card
Hazards
- rubber band snapping near eyes
- skewer points
Controls
- eye protection while winding and releasing
- blunt the skewer ends with tape
Note
No hazardous chemicals or naked flames are used. Complete the school's risk assessment for the activity before the lesson; the NSW Department of Education Science safety and compliance page points to CSIS 1.7 (Risk assessment – a pre-requisite for risk control) for how to carry it out.
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 7–10 Syllabus (2023)SC4-CHG-01SC4-WS-03SC4-WS-06SC4-WS-07
- Australian Curriculum v9AC9S8U05AC9S8I02AC9S8I05AC9S8I07
Sources
The pages the author read to write this activity.