Impulse and Force

Active learning works for Impulse and Force because students often struggle with visualising invisible fields and forces. Hands-on experiments let them observe magnetic forces directly and feel the effects of changing variables like current or angle.

• Year 12
• Physics
• 3 activities
• 20 min–60 min

Learning Objectives

1. Calculate the impulse experienced by an object given its change in momentum.
2. Analyze the relationship between average force, impulse, and the time interval over which the force acts.
3. Evaluate the effectiveness of safety features like crumple zones in reducing impact forces based on impulse principles.
4. Design a simple safety device that minimizes force during an impact by maximizing the time of contact.

Inquiry Circle

⏱ 60 min·Small Groups

Inquiry Circle: Build a DC Motor

Students work in small groups to construct a simple electric motor using a battery, a magnet, and a coil of wire. They must troubleshoot their design and explain how the Right-Hand Rule applies to the motion they observe.

Prepare & details

Explain how crumple zones in cars reduce injury during a collision.

Facilitation Tip: During the DC Motor Build, circulate and ask groups to explain how the commutator reverses current to maintain rotation, rather than just watching it spin.

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

Stations Rotation

⏱ 50 min·Small Groups

Stations Rotation: Magnetic Force Applications

Stations include a mass spectrometer simulation, a loudspeaker teardown, and a 'jumping wire' demonstration. Students rotate to identify how the magnetic force is being used in each specific technology.

Prepare & details

Evaluate the impact of varying contact time on the force experienced during an impact.

Setup: Tables/desks arranged in 4-6 distinct stations around room

Materials: Station instruction cards, Different materials per station, Rotation timer

• Remember
• Understand
• Apply
• Analyze
• Self-Management
• Relationship Skills

Think-Pair-Share

⏱ 20 min·Pairs

Think-Pair-Share: Particle Paths

Students are given diagrams of charged particles entering magnetic fields at different angles. They must predict the resulting path (circular, helical, or straight) and explain their reasoning to a partner before a class-wide check.

Prepare & details

Design a safety device that utilizes the principle of impulse to minimize force.

Setup: Standard classroom seating; students turn to a neighbor

Materials: Discussion prompt (projected or printed), Optional: recording sheet for pairs

• Understand
• Apply
• Analyze
• Self-Awareness
• Relationship Skills

Teaching This Topic

Teach this topic by combining physical models with peer explanations. Avoid over-relying on abstract diagrams alone, since the three-dimensional nature of magnetic fields is hard to grasp from 2D images. Research shows that using the Right-Hand Rule kinesthetically, with students miming directions while holding a wire model, improves spatial understanding.

What to Expect

Successful learning looks like students confidently predicting directions of force, explaining why motors spin, and connecting particle paths to real-world devices. They should articulate the perpendicular relationship between force, velocity, and field.

Watch Out for These Misconceptions

Common Misconception

During the Jumping Wire experiment in Station Rotation, watch for students attributing the wire's movement to the metal being magnetic.

What to Teach Instead

Redirect by asking, 'What happens if we replace the copper wire with an aluminum wire of the same gauge? The wire still moves, proving it is the current that matters, not the metal's magnetic properties.'

Common Misconception

During the Think-Pair-Share activity on Particle Paths, watch for students drawing force vectors parallel to magnetic field lines.

What to Teach Instead

Have students use their hands to model the wire's position and direction of current while tracing the field lines with the other hand, reinforcing the perpendicular relationship.

Assessment Ideas

Quick Check

After the DC Motor Build, ask students to sketch the force direction on the motor's armature and explain how the commutator maintains continuous rotation using impulse concepts.

Discussion Prompt

During the Magnetic Force Applications station, ask students to explain why a loudspeaker's cone moves outward when current flows in one direction and inward when reversed, using impulse and force principles.

Exit Ticket

After the Particle Paths Think-Pair-Share, ask students to write down one example of how a particle accelerator uses magnetic fields to change a particle's direction, and explain how this relates to the Right-Hand Rule.

Extensions & Scaffolding

• Challenge: Ask students to design a modification to their DC motor to reverse its direction without changing the battery polarity.
• Scaffolding: Provide pre-drawn Right-Hand Rule diagrams for the Magnetic Force Applications station, with blanks for students to fill in directions of force.
• Deeper: Have students research how particle accelerators use magnetic fields to steer charged particles, then present a one-slide summary to the class.

Key Vocabulary

Impulse	The product of the average force acting on an object and the time interval over which that force acts. It is equal to the change in momentum of the object.
Momentum	A measure of an object's mass in motion, calculated as the product of its mass and velocity. It is a vector quantity.
Change in Momentum	The difference between an object's final momentum and its initial momentum. This change is directly caused by impulse.
Average Force	The constant force that would produce the same impulse over a given time interval as the actual, often varying, force.