Physics — Algebra and Trigonometry · 40 minutes
Suggested grades 11–12 · Unit 3: Fields and Collision Design · Lesson 2 of 2
Reduce Force by Changing Stopping Time
Evaluate fictional cargo-protection data with impulse reasoning and design constraints.
Mr. S Teaches · Original starter lesson · HS-PHYS-06 · Grade range is planning guidance.Watch, notice, discuss
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Introduction to Impulse & Momentum - Physics
By The Organic Chemistry Tutor
Connect a fixed momentum change with stopping time and average force; use the introductory algebra examples for the packaging comparison.
Open on YouTube: Introduction to Impulse & Momentum - Physics (opens a new tab) ↗Introduction to Momentum, Force, Newton's Second Law, Conservation of Linear Momentum, Physics
By The Organic Chemistry Tutor
Use momentum conservation and force reasoning as a second explanation, then assess stopping-distance and space constraints.
Open on YouTube: Introduction to Momentum, Force, Newton's Second Law, Conservation of Linear Momentum, Physics (opens a new tab) ↗What idea from the video helps you recommend and refine a model packaging design using stopping time, average force and space constraints? Identify one useful example and one limit of the video's model or explanation.
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Learning objective
Recommend and refine a model packaging design using stopping time, average force and space constraints.
Before you begin
- Understand momentum and divide by a time interval.
Gather your materials
- Paper or notebook
- Pencil; calculator optional for numerical work; all task data supplied below
Language to know
- impulse
- Momentum change caused by a force acting over time.
- average force
- A time-averaged force over a specified interval.
- constraint
- A required bound on a design.
Understand the concept
Fictional cargo brief: A 1 kg model package moving at 4 m/s stops without rebounding. Designs A, B and C increase stopping times to 0.02 s, 0.08 s and 0.10 s respectively. They require 1, 4 and 7 cm of space; available space is 5 cm. Use |Favg|=|Δp|/Δt. Longer stopping time reduces average force for the same momentum change, but average force does not reveal the peak. No drops, impacts, helmets or safety equipment are built or tested here.
Teach it step by step
- Read the brief and calculate the common momentum-change magnitude.
- Calculate average force for each design and enter force and space in a matrix.
- Choose among designs meeting the space requirement, then propose a refinement without claiming a tested safety rating.
- Identify a missing peak-force measurement and explain why a real design would need repeated testing.
Make the thinking visible
Worked example or model response
|Δp|=4 kg·m/s. Average forces are A 200 N, B 50 N and C 40 N. C has the lowest modeled average but exceeds the 5 cm constraint; B is the best of the supplied feasible options for minimizing average force.
Guided practice
Together explain why a design that rebounds could have a different momentum change even with the same incoming speed.
Independent practice
Recommend a feasible design, propose a change to its cushioning model and name the force, size and rebound measurements needed to evaluate it. Include the three calculated averages.
Quick assessment
Does halving average force prove that every instantaneous force during a collision is halved?
Answer key & assessment criteria
Answers and teaching guidance
- Guided: Reversing velocity changes momentum by more than simply stopping, so the same incoming speed does not guarantee the same impulse.
- Independent: B is the supplied feasible choice; refinement must be retested against space and force constraints and should include peak force/rebound rather than only averages.
- Quick check: No. Different force-time profiles can have the same average or impulse and different peaks.
Look for: Assess the stated objective using the concrete criteria and explanations in the answer key. Invite an alternative supported solution; distinguish a model’s prediction from an established observation.
Make it work for your learner
More support
Provide a momentum-change box followed by a force/space comparison table.
Extension challenge
Sketch two different force-time rectangles or triangular profiles with the same impulse and discuss why a peak-force criterion could alter the design decision.
Verified references · Selected contributions
Standards connections
Selected NGSS high school-band contribution; full performance requires additional evidence and instruction.
Subject-content standards
These records identify the part of a subject standard practiced here. Course placement is instructional guidance; the source’s category or band remains authoritative.
Contributes to NGSS performance expectation
HS-PS2-3
NGSS · High school band
Evaluate and refine a device that reduces collision forces.
Read the official performance expectation ↗The lesson evaluates and proposes refinements using fictional cargo data. It does not construct or test a device, establish injury prevention or certify real protective equipment.
Verified 2026-11-04. Selected contribution, not full attainment.
Supporting literacy connections
These records apply to the specified reading, writing or communication task. They do not establish subject-content alignment.
Supporting Common Core literacy connection
RST.11-12.1
Common Core · Grades 11–12
Analyze technical details, distinctions and gaps using textual evidence.
Read the official standard ↗The activity explicitly analyzes the provided technical text, table or model. It contributes selected literacy practice rather than complete grade-band reading coverage or independent subject-content alignment.
Verified 2026-11-04. Selected contribution, not full attainment.