Lesson 4: Momentum & Impulse in 1D/2D Collisions
Demonstrating understanding of mechanical principles, motion, forces, and energy for NCEA Level 2 Physics.
🎯 Ngā Whāinga Akoranga | Learning Intentions
Linear momentum (p = mv), impulse (Delta p = F Delta t), conservation of momentum in isolated systems, and elastic vs inelastic collisions.
Calculate vector momentum before and after 1D/2D collisions, and explain crumple zones and airbags using impulse-force-time relationships.
🎥 Media Anchor & Pedagogical Scaffold
Momentum Conservation & Impulse Mechanics
Video Clip: Momentum in collisions — conservation of momentum explained with bowling ball examples (Runtime: 5m 23s).
🧠 1. Before Viewing (Activate & Predict)
Why do car crumple zones and airbags save lives during high-speed collisions by extending impact time?
👁️ 2. During Viewing (Watch With a Job)
- Define: write the formula for momentum. What are the units? Is momentum a scalar or vector quantity?
- State the law: what does conservation of momentum say happens in a closed system? Restate it in your own words.
- Calculate: a 0.5 kg ball moving at 4 m/s strikes a stationary 0.5 kg ball. Using conservation of momentum, what is the combined speed if they stick together?
🗣️ 3. After Viewing & Kaiako Move (Process & Apply)
Kaiako Move: Use dynamics air-track or marble collision ramps to demonstrate 1D momentum conservation hands-on.
Immediate Task: Complete Section 4 of your Mechanics Portfolio: 1D/2D Collision Vector Analysis & Safety Impulse Justification.
⚡ Whakaoho | Do Now: Physics Mechanics Recall (10 mins)
An airbag does not reduce your momentum change. You still go from full speed to zero — the change is identical with or without it.
Two minutes: if Δp is the same either way, what exactly is the airbag changing? Look at Δp = FΔt and say which quantity it stretches and which it therefore shrinks. That single rearrangement explains airbags, crumple zones, catching a ball with soft hands, and why gymnasts land on mats.
📖 Activity 1: Mechanical Investigation & Vector Problem Solving (25 mins)
Conserve it (15 min). Solve three collision problems — one elastic, one inelastic, one explosion. Momentum is a vector, so assign directions before you start and keep the signs. Then check kinetic energy before and after, and state which collisions conserved it and which did not.
Impulse in practice (10 min). Calculate the average force on a driver stopping in 0.1 s versus 0.5 s from the same speed. Compare the two numbers, then explain a crumple zone using them rather than describing it.
📝 Activity 2: Level 2 Physics Portfolio Task & Merit/Excellence Scaffolding (20 mins)
Portfolio — Section 4. Submit: (1) three collision problems with directions assigned and momentum conservation shown; (2) your kinetic energy check identifying elastic and inelastic; (3) the two impulse forces calculated and a crumple-zone explanation built on those numbers.
🏫 Kaiako Planning & Pedagogy Notes
NCEA Level 2 Alignment: Direct preparation for Level 2 Physics (Demonstrate understanding of mechanics). Emphasise linking mathematical working directly to physical concept explanations for Merit/Excellence grades.