Making Impacts Safer

Active learning works for this topic because force and momentum are abstract ideas that become concrete when students physically manipulate materials and observe collisions. When students drop eggs or test toy cars, they directly witness how padding changes outcomes, making the impulse-momentum theorem tangible rather than theoretical.

• 5th Year
• Principles of the Physical World: Senior Cycle Physics
• 4 activities
• 30 min–50 min

Learning Objectives

1. Calculate the impulse experienced by an object during a collision, given initial and final velocities and contact time.
2. Compare the peak forces experienced by an object landing on a hard surface versus a padded surface, using impulse-momentum calculations.
3. Explain how increasing the duration of a collision reduces the average force exerted, using the impulse-momentum theorem.
4. Analyze the design of safety equipment, such as helmets and airbags, in terms of their ability to increase impact time and reduce injury.

⏱ 50 min·Small Groups

Egg Drop Lab: Padding Designs

Provide eggs, tape, and materials like bubble wrap, foam, and newspaper. Students in groups design and build protective padding, drop eggs from 2 meters, and video impacts to measure contact time. Discuss which designs best extend time and prevent breakage.

Prepare & details

Why do playgrounds have soft surfaces?

Facilitation Tip: During the Egg Drop Lab, circulate with a force sensor and ask groups to watch how the padding material changes the force peak on their graphs as they vary thickness and type.

⏱ 35 min·Pairs

Video Analysis: Hard vs Soft Landings

Drop steel balls from 1 meter onto concrete and mats. Pairs use phone slow-motion video to count frames during impact and calculate average force with F = mΔv/Δt. Compare results and graph force reductions.

Prepare & details

How do helmets protect your head?

Facilitation Tip: For the Video Analysis, play the high-speed clips frame by frame to let students count how many frames the object takes to stop on each surface.

⏱ 45 min·Small Groups

Toy Car Crash Test: Crumple Zones

Roll toy cars down ramps into barriers with varying padding. Groups measure stopping distances and times, estimate forces, and redesign barriers for safer stops. Share data class-wide.

Prepare & details

What happens if you jump onto a hard floor versus a soft mat?

Facilitation Tip: In the Toy Car Crash Test, ensure students measure crumple zone deformation and compare it to undamaged cars to connect material choice to energy absorption.

⏱ 30 min·Whole Class

Helmet Demo: Fruit Impacts

Drop water-filled balloons or small fruits with and without helmet foam onto surfaces. Whole class observes cracking patterns and times impacts with stopwatches. Analyze why padding matters for head protection.

Prepare & details

Why do playgrounds have soft surfaces?

Teaching This Topic

Teach this topic by starting with the Egg Drop Lab so students experience the core idea firsthand. Avoid rushing to the formula; let students discover the relationship between time and force through measurement before introducing the impulse-momentum theorem. Research shows that students grasp impulse better when they first see the visual difference in collision durations.

What to Expect

Successful learning looks like students confidently linking padding to increased collision time and reduced force, not just memorizing the formula. You will see students using data from their tests to justify why certain materials protect better, and applying the impulse-momentum theorem to explain real-world safety designs.

Watch Out for These Misconceptions

Common Misconception

During the Egg Drop Lab, students may think padding absorbs all kinetic energy and eliminates force entirely.

What to Teach Instead

During the Egg Drop Lab, remind students to check their force-time graphs; they will see lower peaks but not zero force, reinforcing that padding spreads out the force over time rather than eliminating it.

Common Misconception

During the Video Analysis, students may assume that the drop height alone determines the force of impact regardless of surface.

What to Teach Instead

During the Video Analysis, have students pause the clip at the moment of impact and measure the time to full stop on each surface; this visual evidence will show how soft surfaces extend collision time and reduce force.

Common Misconception

During the Toy Car Crash Test, students may believe thicker padding always provides more protection.

What to Teach Instead

During the Toy Car Crash Test, ask students to test stacked materials and plot force peaks; they will discover that beyond a certain thickness, rebound increases force again, showing that optimal protection requires balancing time and rebound.

Assessment Ideas

Quick Check

After the Video Analysis, present students with two scenarios: a cyclist falling onto asphalt and a cyclist falling onto grass. Ask them to write one sentence explaining which scenario results in less force on the cyclist and why, referencing the contact time observed in the videos.

Discussion Prompt

During the Helmet Demo, pose the question: 'If a helmet is designed to protect your head, how does it achieve this protection?' Facilitate a discussion where students explain the role of foam padding in increasing impact time and decreasing force using the impulse-momentum theorem and observations from the fruit impact demo.

Exit Ticket

After the Egg Drop Lab, give students a scenario: An object with a momentum change of 10 kg m/s hits a surface. If it hits a hard surface for 0.01 seconds, what is the average force? If it hits a soft surface for 0.1 seconds, what is the average force? Students calculate and write both forces, using their lab data as a reference.

Extensions & Scaffolding

• Challenge students to design a protective case for a smartphone using no more than three common materials, testing drop heights until the phone survives.
• For students struggling to connect force-time graphs to safety, provide a scaffolded worksheet that guides them through labeling peak force, contact time, and momentum change on sample graphs.
• Deeper exploration: Have students research how airbags use sensors and gas generators to control deployment timing and force, linking their lab findings to automotive engineering.

Key Vocabulary

Impulse	The change in momentum of an object, calculated as the product of the average force and the time interval over which the force acts.
Momentum	A measure of an object's mass in motion, calculated as the product of its mass and velocity.
Deceleration	The rate at which an object slows down; a decrease in velocity over time.
Contact Time	The duration for which two objects are in physical contact during a collision or impact.