Physics 11–12 · Year 11

Motion of a cart on an inclined plane (syllabus practical)

Module 2: Dynamics (Forces)

Practical, model not builtLow risk

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The idea

On a slope the weight component along the incline, less friction, sets a constant acceleration that can be predicted from the angle and checked by measurement.

What you need

Low-friction dynamics cart (about 0.5 kg) and a 1.2 m track or smooth board
Two light gates with timer, or a motion sensor, or a phone running Tracker video analysis
Protractor or a metre rule and set square to find the angle from rise and run
Retort stand and boss to set the incline at 5, 10, 15 and 20 degrees
Electronic balance

How to do it

Set the track at 10 degrees; measure rise and run and compute the angle with tan.
Release the cart from rest at a start mark and time it over the next 1.00 m with the clock started at release (a motion sensor, video, or a release switch with a light gate at the 1.00 m mark), because a = 2 s / t^2 holds only for a start from rest; repeat five times (the NSW Department of Education Module 1 guide runs carts up and down inclined planes with light gates, motion sensors or video).
Predict the acceleration from a = g sin(theta) before measuring; then compute the measured acceleration from a = 2 s / t^2.
Repeat at 5, 15 and 20 degrees and plot measured a against sin(theta).
The gradient of a against sin(theta) is g if friction is negligible; a non-zero intercept measures rolling resistance.
Extension: repeat with a solid ball instead of the cart and explain the lower value.

What you should see

At 10 degrees the frictionless prediction is a = 9.806 65 x sin(10 degrees) = 1.703 m/s^2; friction lowers the measured value, and with a rolling-resistance coefficient of 0.05 the prediction falls to 1.220 m/s^2. A solid ball rolls at 5/7 of the frictionless value, 1.216 m/s^2, because part of its energy goes into rotation (the Module 2 guide's caution). The a against sin(theta) plot is linear with gradient near 9.8 m/s^2.

What changes

What you change: angle of incline
What you measure: acceleration of the cart
What you keep the same: same cart and track
release from rest
same timing distance

Common misconceptions

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

A heavier cart accelerates faster down the same slope; mass cancels and only the angle and friction matter.
The normal force equals the weight on a slope; it equals the weight times cos(theta).

Safety card

Low riskLearners carry it out

Hazards

cart leaving the track
stand tipping at steep angles

Controls

catch box or padded stop at the bottom
clamp the stand

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 PH11/12-2
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-02
Australian Curriculum v9No Australian Curriculum v9 code is listed.

Sources

The pages the author read to write this activity.

All Concept Studio activities