Physics · Year 11

Active learning ideas

Momentum and Impulse

Active learning works for momentum and impulse because students need to feel the difference between a sharp jolt and a cushioned stop. When they measure collisions with trolleys, wrap eggs in bubble wrap, or graph force over time, the abstract equations p = mv and J = FΔt become concrete experiences they can trust and explain.

• ACARA Content Descriptions
• AC9SPU07

• 30–60 min
• Pairs → Whole Class
• 4 activities

Activity 01

• Inquiry Circle
• 50 min · Pairs

Trolley Collision Investigation: Impulse Measurement

Set up a low-friction track with motion sensors or photogates. Pairs launch trolleys of varying masses into collisions, record pre- and post-velocities, and calculate Δp. Compare results to force-time graphs from data loggers, then discuss how changing collision time affects force.

Explain the relationship between impulse and change in momentum.

Facilitation Tip

During the Trolley Collision Investigation, place a piece of masking tape on the track where the trolley starts so every group begins from the same reference point for consistent measurements.

What to look for

Present students with a scenario: A 2 kg ball moving at 5 m/s collides with a wall and stops. Ask them to calculate the ball's initial momentum, its final momentum, and the impulse delivered by the wall. They should show their calculations.

• Analyze
• Evaluate
• Create
• Self-Management
• Self-Awareness

Activity 02

• Inquiry Circle
• 60 min · Small Groups

Egg Drop Design: Force Minimization

Provide materials like straws, cushions, and tape. Small groups build protective devices for eggs dropped from 2 meters, aiming to extend impact time. Measure deceleration with video analysis or accelerometers, calculate impulses, and redesign based on peer feedback.

Analyze how the impulse-momentum theorem explains the reduction of force during a long-duration impact.

Facilitation Tip

For the Egg Drop Design, provide only one sheet of graph paper per group to encourage focused sketches of proposed designs before building begins.

What to look for

Pose this question: 'Imagine catching a fast-moving baseball. Why is it easier to catch if you move your hand backward as you make contact? Explain your answer using the terms impulse and momentum.'

• Analyze
• Evaluate
• Create
• Self-Management
• Self-Awareness

Activity 03

• Inquiry Circle
• 45 min · Small Groups

Marble Ramp Collisions: Momentum Transfer

Construct ramps leading to a collision zone on a flat surface. Groups vary marble sizes or numbers, video-record collisions in slow motion, and compute momentum changes. Predict outcomes for elastic versus inelastic cases before testing.

Predict the effect of increasing impact time on the force experienced during a collision.

Facilitation Tip

In the Marble Ramp Collisions, use a level ramp and mark a starting line with a dry-erase marker so friction variations do not skew momentum changes across trials.

What to look for

Provide students with two impact scenarios: Scenario A (short impact time) and Scenario B (long impact time), with equal changes in momentum. Ask them to state which scenario involves a larger force and to briefly justify their answer using the impulse-momentum theorem.

• Analyze
• Evaluate
• Create
• Self-Management
• Self-Awareness

Activity 04

• Inquiry Circle
• 30 min · Whole Class

Bungee Impulse Demo: Whole Class Prediction

Suspend masses on elastic cords over increasing drops. The class predicts force-time curves, then uses force sensors to measure impulses. Debrief collectively on how stretch time reduces peak force.

Explain the relationship between impulse and change in momentum.

Facilitation Tip

During the Bungee Impulse Demo, have students sketch their force-time graphs on mini-whiteboards first so they can revise predictions before seeing the sensor output.

What to look for

Present students with a scenario: A 2 kg ball moving at 5 m/s collides with a wall and stops. Ask them to calculate the ball's initial momentum, its final momentum, and the impulse delivered by the wall. They should show their calculations.

• Analyze
• Evaluate
• Create
• Self-Management
• Self-Awareness

A few notes on teaching this unit

Teach this topic by letting students experience the variables first and derive the equations second. Start with a quick live demo of a ball bouncing off a force sensor to show how force changes over time, then guide students to measure impulse by finding the area under the curve. Avoid starting with lectures on p = mv, as students grasp momentum better when they see how mass and velocity both contribute to collision outcomes. Research shows that when students manipulate materials and collect their own data, their misconceptions about force and time diminish faster than with traditional instruction.

Students will move from calculating impulse formulas to justifying why padding reduces force in real collisions. By the end of these activities, they should predict outcomes, interpret graphs, and justify designs using the impulse-momentum theorem with clear connections to data and evidence.

---

Watch Out for These Misconceptions

• During the Trolley Collision Investigation, watch for students who say momentum depends only on speed and ignore mass.

  Have students calculate momentum for trolleys of different masses but the same starting velocity, then graph p vs. m. Ask them to explain why the heavier trolley transfers more impulse to the barrier in collisions.

• During the Egg Drop Design, watch for students who think longer collision time increases impulse.

  Challenge teams to measure Δt with a stopwatch and calculate J = FΔt using force plate data. Ask them to compare impulse values across trials to see that Δp stays the same even as Δt changes.

• During the Bungee Impulse Demo, watch for students who assume force is constant during a collision.

  Guide students to trace the force-time graph and calculate the area under the curve for impulse. Ask them to compare their predicted Δp to the measured change in momentum to correct the misconception.

---

Methods used in this brief

• Inquiry Circle