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.

• Year 11
• Physics
• 4 activities
• 30 min–60 min

Learning Objectives

1. Calculate the momentum of an object given its mass and velocity.
2. Determine the impulse applied to an object using its change in momentum.
3. Explain the impulse-momentum theorem using a real-world example of impact reduction.
4. Analyze how increasing impact time affects the magnitude of force during a collision.
5. Predict the change in momentum for a system undergoing a collision.

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.

Prepare & details

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.

Setup: Groups at tables with access to source materials

Materials: Source material collection, Inquiry cycle worksheet, Question generation protocol, Findings presentation template

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

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.

Prepare & details

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.

Setup: Groups at tables with access to source materials

Materials: Source material collection, Inquiry cycle worksheet, Question generation protocol, Findings presentation template

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

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.

Prepare & details

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.

Setup: Groups at tables with access to source materials

Materials: Source material collection, Inquiry cycle worksheet, Question generation protocol, Findings presentation template

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

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.

Prepare & details

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.

Setup: Groups at tables with access to source materials

Materials: Source material collection, Inquiry cycle worksheet, Question generation protocol, Findings presentation template

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

Teaching This Topic

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.

What to Expect

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

Common Misconception

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

What to Teach Instead

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.

Common Misconception

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

What to Teach Instead

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.

Common Misconception

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

What to Teach Instead

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.

Assessment Ideas

Quick Check

After the Trolley Collision Investigation, present students with a 3 kg trolley moving at 2 m/s that collides and stops. Ask them to calculate initial momentum, final momentum, and impulse delivered by the barrier, showing full calculations on paper.

Discussion Prompt

During the Egg Drop Design, ask groups to explain why moving their hand backward when catching a fast ball makes the catch easier, using impulse and momentum in their responses.

Exit Ticket

After the Marble Ramp Collisions, provide two scenarios with equal Δp but different Δt. Ask students to identify which scenario has larger force and justify with the impulse-momentum theorem in 2–3 sentences.

Extensions & Scaffolding

• Challenge students to design a landing pad for a 50 g marble dropped from 1 m that stops it in under 0.2 s with force below 2 N.
• For students who struggle, provide pre-labeled force sensors and step-by-step graph interpretation cards to help them connect area under the curve to impulse.
• Deeper exploration: Ask students to derive the impulse-momentum theorem from Newton’s second law and F = ma using the trolley collision data and kinematic equations in a mini-investigation.

Key Vocabulary

Momentum	A vector quantity representing an object's mass in motion, calculated as the product of its mass and velocity (p = mv).
Impulse	The change in momentum of an object, equal to the product of the net force acting on it and the time interval over which the force is applied (J = FΔt).
Impulse-Momentum Theorem	A physics principle stating that the impulse applied to an object is equal to its change in momentum (J = Δp).
Collision	An event in which two or more bodies exert forces on each other over a relatively short time interval.