Physics 11–12 · Year 11
Momentum in one- and two-dimensional collisions (syllabus practical)
Module 2: Dynamics (Momentum, Energy and Simple Systems)
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The idea
In a closed system the total momentum before a collision equals the total after, whether or not kinetic energy is conserved.
What you need
- Two dynamics carts with magnetic bumpers (elastic) and velcro or plasticine ends (inelastic), or two gliders on a linear air track
- Two light gates with timer, or a phone video for Tracker analysis
- Slotted masses to load one cart, electronic balance
- For two dimensions: two marbles or air-hockey pucks on a large sheet of paper, filmed from above
How to do it
- Weigh both carts. Level the track.
- Elastic run: push cart A (0.500 kg) at cart B (0.500 kg) at rest with magnetic bumpers facing; record both speeds before and after with the light gates.
- Repeat with cart B loaded to 1.000 kg, then with the velcro ends so the carts stick.
- For each run compute total momentum and total kinetic energy before and after; five repeats per case.
- Two-dimensional run: film two marbles colliding off-centre from above; measure velocity components with Tracker and add the momentum vectors.
What you should see
Equal masses, elastic: A stops and B moves off at A's speed. A (0.500 kg) at 1.00 m/s striking a 1.000 kg cart at rest elastically: A rebounds at 0.333 m/s and B moves at 0.667 m/s. The same masses sticking together move at 0.333 m/s, momentum 0.500 kg m/s is conserved, and kinetic energy falls from 0.250 J to 0.083 J. The learner knows it worked when the momentum totals before and after agree within about 5 per cent on a level, low-friction track.
What changes
- What you change
- type of collision and mass of the target cart
- What you measure
- velocities after the collision
- What you keep the same
- level track
- same initial speed
- carts start from rest except the projectile
Common misconceptions
Each of these ideas is wrong, and the activity is a chance to test it.
- Momentum is lost in a sticky collision; kinetic energy is lost, momentum is not.
- The heavier cart exerts the larger force during the collision; the forces are equal and opposite.
Safety card
Hazards
- carts running off the track
- strong magnets pinching fingers
Controls
- padded stops
- keep magnets away from phones and cards
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 2027PH11-9PH11/12-2
- Physics 11-12 Syllabus (2025), not yet taught: Year 11 from Term 1 2027, Year 12 from Term 4 2027, first HSC examination 2028PY-11-01PY-11WS-03
- Australian Curriculum v9No Australian Curriculum v9 code is listed.
Sources
The pages the author read to write this activity.
- www.nsw.gov.au/sites/default/files/noindex/2025-03/physics-stage-6-syllabus-2017.docx
- education.nsw.gov.au/content/dam/main-education/teaching-and-learning/curriculum/key-learning-areas/science/s-6/physics/Physics-module-2-guide.docx
- phet.colorado.edu/en/simulations/collision-lab
- curriculum.nsw.edu.au/learning-areas/science/physics-11-12-2025/outcomes