Level 2 · Secondary physics teaching kit · Grades 10–12
Mechanics and conservation laws
Use the learner record during the live investigation, then use the instructor guide to facilitate comparison, address misconceptions, and assess evidence-bounded reasoning.
Learner lab record
Collision momentum and energy audit
Which quantities remain conserved when two carts collide, and what changes when they stick or rebound?
Setup
Use the collision laboratory. Hold the two masses fixed while comparing an elastic case with a sticking case, then change one mass and repeat.
Predict first
- 1. Predict the final direction of the system momentum.
- 2. Predict which collision preserves kinetic energy and which transfers it into other forms.
| Variable | Role | Unit |
|---|---|---|
| Cart masses | controlled, then independent | kg |
| Initial velocities | independent | m/s |
| Final velocities | dependent | m/s |
| Total momentum and kinetic energy | calculated | kg·m/s and J |
Observation columns
Analyze
- 1. Which before/after residual is closest to zero?
- 2. Where does kinetic energy go in the sticking model?
- 3. Why must the system include both carts?
- 4. Name one external impulse that would weaken the comparison.
Conclusion frame
Across ___ collision models, total momentum changed by ___ while kinetic energy changed by ___ because ___.
Instructor guide · 45–55 minutes
Teach the investigation, not the interface
Learning target: Learners use a declared system boundary to distinguish momentum conservation from kinetic-energy conservation.
Prepare
- • Review signed velocity and system boundaries.
- • Prepare one equal-mass and one unequal-mass case.
- • Define an acceptable numerical residual before the activity.
Facilitation moves
- • Ask for the system boundary before any equation.
- • Require signed momentum rather than speed alone.
- • Have groups exchange settings and reproduce one another's ledger.
Accessibility and participation
- • Pair arrows with signed numbers so direction is not color-dependent.
- • Offer a preformatted ledger and calculator access.
- • Allow keyboard entry for every model control.
Evidence of learning
- • A complete signed momentum ledger
- • A correct kinetic-energy comparison
- • A defended system boundary
Misconception checks
Momentum and kinetic energy are always both conserved.
Momentum is conserved in an isolated collision; kinetic energy is conserved only in the elastic idealization.
A stopped cart has no effect on the ledger.
Its mass and final motion still belong to the two-cart system.
Extension
Introduce a measured external impulse and test whether the corrected momentum ledger closes.