Explicit physics instruction
Collision analysis combines system momentum, kinetic-energy accounting, and force-time evidence. Each representation answers a different question.
Engineering safety often aims to reduce peak force by increasing interaction time or distance while managing the same momentum change.
A defensible design claim should state what is conserved, what changes form, and which criterion is optimized.
Vocabulary: collision model; impulse; kinetic energy; design criterion; tradeoff.
Worked example with reasoning
A crumple zone increases stopping distance/time. The vehicle’s momentum still changes to near zero, but the longer impulse interval can reduce average and peak force on occupants.
Guided question
Write a CER comparing a rigid-stop design with a padded-stop design for the same initial momentum.
Independent work
- Submit one collision classification with calculations.
- Interpret one force-time graph.
- Write one safety-design CER.
- Record one corrected misconception.
Spiral retrieval bridge
- From Week 15: state the external-impulse condition for momentum conservation.
- From Week 14: relate impulse to force-time area.
- From Week 12: distinguish energy from power.
- From Week 10: explain the v² dependence of kinetic energy.
Misconception check
Safety design does not 'absorb momentum'; momentum change is delivered by impulse while energy is redistributed and dissipated.
Formative understanding check
What design variable can lower average force for a fixed Δp?
Reveal response
Increasing the time over which the momentum change occurs.
Mentor evidence conference
Ask Archaemenes to compare momentum, energy, and impulse representations for consistency.
Teacher guidance
Foundation: Use an impulse-design sentence frame.
Core: Integrate momentum, KE, and force-time evidence.
Extended: Evaluate tradeoffs among force reduction, deformation distance, and system constraints.