Physics 11–12 · Year 12

Centripetal acceleration on a turntable measured with a phone accelerometer

Module 5: Advanced Mechanics (Circular Motion)

Practical, model not builtLow risk

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

At a fixed rotation rate the centripetal acceleration grows in proportion to the radius and points towards the axis.

What you need

Record turntable at 33 1/3 and 45 revolutions per minute, or a lazy Susan spun at a measured rate
Phone running phyphox centripetal acceleration (records radial acceleration and gyroscope rate), taped in place; ruler; stopwatch
Optional wireless accelerometer (the NSW Department of Education Module 5 guide activity)

How to do it

Predict the direction the accelerometer will report before spinning (the guide's predict-then-measure task).
Tape the phone with its sensor 10.0 cm from the axis; spin at 33 1/3 rpm and record the radial acceleration for 20 s.
Move the sensor to 15.0 cm and repeat; then use 45 rpm at 10.0 cm.
Plot acceleration against radius at fixed rate and against the square of the angular speed at fixed radius.

What you should see

At 33 1/3 rpm (omega = 3.49 rad/s) the phone reads 1.22 m/s^2 at 10.0 cm and 1.83 m/s^2 at 15.0 cm, directed towards the axis; at 45 rpm and 10.0 cm it reads 2.22 m/s^2. If readings differ from these, the sensor inside the phone is probably not at the marked radius; dividing the reading by the square of the angular speed phyphox measures gives the sensor's true radius.

What changes

What you change: radius, then rotation rate
What you measure: centripetal acceleration
What you keep the same: rotation rate (series 1) or radius (series 2)
phone taped flat

Common misconceptions

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

The accelerometer will read outward because that is the direction you feel pushed; the acceleration is inward.
Constant speed means zero acceleration; the direction is changing, so there is acceleration.

Safety card

Low riskLearners carry it out

Hazards

phone flying off the turntable

Controls

tape firmly, use a phone case, no faster than 45 rpm

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 2027PH12-12 PH11/12-5
Physics 11-12 Syllabus (2025), not yet taught: Year 11 from Term 1 2027, Year 12 from Term 4 2027, first HSC examination 2028PY-12-01 PY-12WS-03
Australian Curriculum v9No Australian Curriculum v9 code is listed.

Sources

The pages the author read to write this activity.

All Concept Studio activities