Physics 11–12 · Year 11

Rolling resistance of a toy car from its stopping distance

Module 2: Dynamics (Forces, Acceleration and Energy)

Practical, model not builtLow risk

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The idea

Work done against rolling resistance removes the car's kinetic energy over its stopping distance, so speed and distance give the resistive force.

What you need

Toy car (about 27 g, as in the NSW Department of Education Module 2 guide) and up to 5 m of toy-car track laid level
Light gate and timer, or a phone video at 60 frames per second
Measuring tape, electronic balance

How to do it

Weigh the car and measure the length of the car (the light-gate flag).
Push the car through the light gate and record the entry speed v; measure the distance d it rolls before stopping.
Take ten runs at different speeds and tabulate v^2 against d.
From 0.5 m v^2 = F d, the resistive force is F = m v^2 / (2 d) and the coefficient of rolling resistance is F / (m g) = v^2 / (2 g d).

What you should see

v^2 against d is a straight line. The Module 2 guide's own run with a 26.6 g car on this track gave a deceleration of 0.4 m/s^2, so the coefficient of rolling resistance is 0.4 / 9.8 = 0.04. At that coefficient an entry speed of 1.00 m/s stops the car in 1.00^2 / (2 x 0.04 x 9.806 65) = 1.27 m, well inside a 5 m track, while an entry speed of 1.90 m/s uses nearly all of it (4.60 m). A coefficient of 0.04 is far below the 0.23 the same guide measured for a steel retort stand sliding on a benchtop, which is why the car rolls so far.

What changes

What you change: entry speed
What you measure: stopping distance
What you keep the same: level track
same car
same track surface

Common misconceptions

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

The car stops because it runs out of force; it stops because a small resistive force does negative work on it.
Rolling resistance and sliding friction are the same size; rolling resistance is far smaller.

Safety card

Low riskLearners carry it out

Hazards

trip hazard from a long track on the floor

Controls

lay the track along a wall

Note

Record the activity in RiskAssess (https://www.riskassess.com.au/) and follow the Science ASSIST risk management information sheet (https://asta.edu.au/resource/ais-risk-management-and-risk-assessment/).

Curriculum references

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

Physics Stage 6 Syllabus (2017), current: Year 11 until the end of 2026, Year 12 until Term 3 2027PH11-9 PH11/12-4
Physics 11-12 Syllabus (2025), not yet taught: Year 11 from Term 1 2027, Year 12 from Term 4 2027, first HSC examination 2028PY-11-01 PY-11WS-03
Australian Curriculum v9No Australian Curriculum v9 code is listed.

Sources

The pages the author read to write this activity.

All Concept Studio activities