G8 C02 W3: Week 3 Content - Kairos Academy Skip to main content

Week 3: Week 3 Content

Grade 8 Science | Rosche | Kairos Academies

Text-to-Speech: Chrome (Right-click → "Read aloud") | Edge (Icon in address bar)
Need Support?: Look for green and red "Hint" and "Walkthrough" boxes!

Choose Your Path: Select one of the following investigation pathways based on your interests: - Path A: Biological Force Pairs - Analyze how animals use Newton's 3rd Law to run, swim, and fly - Path B: Collision Physics - Use PhET simulations to measure forces in vehicle crashes - Path C: Space Propulsion - Design rocket systems using action-reaction principles

Specialist Track: As you progress, you'll develop expertise in force pair analysis and system modeling. Advanced learners: Calculate Earth's acceleration when you jump (Challenge at bottom).

Career Connection: Biomechanics engineers, aerospace engineers, and crash test analysts use Newton's Third Law daily. High school physics builds on these force concepts with momentum and impulse.

You're in Control: Design your own force pair demonstration to answer: How can we prove forces are always equal and opposite? Use the scientific method, but YOU decide the objects, procedure, and measurement strategy.

Skip to main content

Accessibility & Learning Support

  • Need text read aloud? Chrome: Right-click then "Read aloud" | Edge: Click speaker icon in address bar
  • Working from home? Look for the HOME ALTERNATIVE boxes at each station
  • Need extra support? Click the green "Need help?" buttons for hints and sentence starters
  • Stuck? Look for the red "Stuck?" boxes with step-by-step help

NGSS Standards Covered This Week

MS-PS2-1 (Primary)

What it means: Apply Newton's Third Law to design a solution to a problem involving the motion of two colliding objects.

In student language: I can use Newton's 3rd Law (action-reaction pairs) to explain and predict what happens when objects collide or interact.

3-Dimensional Learning

Dimension What You'll Practice
SEP-4 Analyzing and Interpreting Data Analyze collision data from PhET simulation
DCI PS2.A Forces and Motion Master Newton's Third Law and force pairs
CCC-4 Systems and System Models Identify which forces act on which objects

Success Criteria - How You'll Know You've Got It

Target 1: Apply Newton's Third Law - Every force has an equal and opposite partner

Self-check: Can I identify action-reaction pairs in collisions and animal motion?

Target 2: Explain why force pairs don't cancel out (they act on different objects)

Self-check: Can I explain why you move when you push a wall, even though forces are equal?

Target 3: Calculate different accelerations from equal forces using a=F/m

Self-check: Can I explain why an elephant and mouse exert equal forces but have different accelerations?

Why This Matters to YOU:

Every time you walk, swim, or jump, you use Newton's Third Law! When you push the ground backward, the ground pushes you forward with equal force. This is how all animal motion works—from cheetahs chasing prey to fish swimming upstream. Understanding force pairs explains car safety (airbags), rocket launches, and even why you can't run on ice!

The Phenomenon: The Gravity Paradox

Consider this mind-bending thought experiment:

  • Earth pulls you downward with the force of gravity (your weight)
  • According to Newton's Third Law, you must pull Earth upward with an equal force
  • But when you jump, only YOU accelerate upward - Earth doesn't move!
  • If forces are equal, why do accelerations differ?

Even stranger: When you jump off a boat, both you AND the boat move! Why does Earth stay still but the boat moves?

Focus Question: How do force pairs work, and why don't they cancel out?

Learning Targets

By the end of this week, you will be able to:

Dr. Mae Jemison: Forces in Space

Dr. Mae Jemison (1956–present) is an engineer, physician, and NASA astronaut who became the first African American woman to travel to space aboard the Space Shuttle Endeavour in 1992. Her journey into space required a deep understanding of Newton's Third Law—the very principle you're studying this week.

During her eight days in orbit, Dr. Jemison experienced Newton's Third Law in action constantly. When the rocket launched, it expelled hot gas downward with tremendous force, and by Newton's Third Law, the gas pushed the rocket upward with equal force—even though the rocket was massive. This is the same principle you'll explore today: equal forces producing different accelerations because of mass differences (a = F/m).

In space, Newton's Third Law becomes even more obvious. When astronauts push off a wall, they float backward because the wall pushes them with equal force. Dr. Jemison had to master force pair concepts to move safely in microgravity—the same concepts you're learning today.

Beyond her NASA career, Dr. Jemison founded the Jemison Group, a technology consulting firm, and leads the 100 Year Starship project—an initiative to develop capabilities for human interstellar travel. Her work demonstrates that understanding fundamental physics principles like Newton's Third Law opens doors to extraordinary achievements. As you learn about force pairs this week, you're building the same foundation that enabled Dr. Jemison to reach the stars.

Why This Matters in St. Louis

Newton's Third Law shapes St. Louis transportation and safety daily. MetroLink uses force pairs for braking—wheels push tracks backward, tracks push train forward. When cars collide on I-64/I-70, equal forces cause different damage based on mass (a=F/m)—why small cars sustain more damage than trucks. St. Louis athletes (Cardinals, Blues, CITY SC) use ground reaction forces for acceleration—the exact physics you're learning this week!

Vocabulary

Key Vocabulary (7 terms) — Practice Tool

Cognate Strategy: Many science words look similar in English and Spanish — use your Spanish to learn science!

Term Spanish Definition
force pair par de fuerzas Two equal and opposite forces acting on different objects
action-reaction acción-reacción Newton's Third Law: every force has an equal opposite partner
Newton's Third Law Tercera Ley de Newton For every action, there is an equal and opposite reaction
system sistema The objects we are analyzing in a situation
collision colisión When two objects hit each other
simultaneous simultáneo Happening at the same time
acceleration aceleración Change in velocity (speed or direction)

Worked Example

Common Mistake: "Objects need force to keep moving"

WRONG: "Objects stop moving when the force runs out."

RIGHT: "Objects keep moving at constant speed unless a force acts on them (Newton's First Law). Friction is the force that slows things down, not "running out of force.""

Common Mistake

Target 4: Identify biological force pairs in animal locomotion

Self-check: Can I identify force pairs when a cheetah runs or a fish swims?

Step-by-Step Problem Solving

Problem Scenario

Review the problem scenario and work through each step below.

↑ Back to Navigation
Need extra support? Click here for hints and sentence starters

Key Concept Reminder:

  • Newton's Third Law: For every action, there is an equal and opposite reaction
  • Force pairs ALWAYS have equal magnitude (strength)
  • Force pairs ALWAYS have opposite directions
  • Force pairs act on DIFFERENT objects (this is why they don't cancel!)

Sentence Starters:

  • "Ball 1's momentum changed by ___ kg·m/s, and Ball 2's momentum changed by ___ kg·m/s."
  • "Even though the masses are different, the momentum changes are equal because..."
  • "Equal momentum changes in equal time means equal forces (Impulse = F×t = Δp)"

Word Bank:

equal, opposite, simultaneous, different objects, Newton's Third Law, force pair, collision

Stuck? Click here for step-by-step help

Try these steps in order:

  1. Open the PhET simulation link above
  2. Click the "Intro" tab at the bottom of the simulation
  3. Find the mass sliders on each ball - set Ball 1 to 0.5 kg, Ball 2 to 1.5 kg
  4. Find the velocity controls - set Ball 1 to +2 m/s, Ball 2 to 0 m/s
  5. Check "Momentum" and "Values" boxes on the right panel to see numbers
  6. Write down the momentum for each ball BEFORE you click play
  7. Click the green PLAY button and let the collision happen
  8. Write down the momentum for each ball AFTER - calculate the change (Δp) for each
  9. The momentum changes should be equal and opposite! This proves equal forces.
  10. Still stuck? Email Mr. Rosche with your screenshot

COMPLETE THE STATION 1 FORM BELOW

Use the PhET simulation to answer questions about force pairs in collisions.

[EMBED G8.C2.W3 Station 1 Form Here]

Form ID: ________________

Station 2 - Biological Force Pairs (C3 Bridge) ⭐ CRITICAL

20 Points | ~15 Minutes

Your Mission: Identify Force Pairs in Animal Locomotion

Why This Matters for Cycle 3:

Next cycle, you'll analyze predator-prey dynamics using force pairs. A cheetah chasing a gazelle, a hawk diving for a rabbit—all require Newton's Third Law! This station prepares you for that work.

Biological Force Pair Examples:

Animal Action Force (Animal → Environment) Reaction Force (Environment → Animal) Result
Cheetah running Paw pushes ground backward Ground pushes paw forward Cheetah accelerates forward
Fish swimming Tail pushes water backward Water pushes tail forward Fish moves forward
Bird flying Wings push air down and back Air pushes wings up and forward Bird stays aloft and moves
Gazelle jumping Legs push ground down Ground pushes legs up Gazelle jumps vertically

C3 PREVIEW ACTIVITY: Cheetah Force Calculation

Let's preview Cycle 3 content using what you learned in Week 2 (F=ma):

SCENARIO:

A 50 kg cheetah accelerates at 10 m/s² when chasing prey. Calculate the force the cheetah's paw exerts on the ground.

STEP 1: Use F=ma from Week 2

F = ma = 50 kg × 10 m/s² = 500 N backward on ground

STEP 2: Apply Newton's Third Law (this week!)

If cheetah pushes ground with 500 N backward, ground pushes cheetah with 500 N forward (equal-opposite pair)

ANSWER:

The cheetah exerts 500 N on the ground (backward), and by Newton's Third Law, the ground exerts 500 N on the cheetah (forward). This 500 N forward force causes the cheetah's 10 m/s² acceleration!

Need extra support? Click here for hints

Force Pair Strategy:

  • Step 1: Identify the two objects interacting (e.g., cheetah and ground)
  • Step 2: Name the action force (e.g., cheetah pushes ground backward)
  • Step 3: Name the reaction force (ground pushes cheetah forward)
  • Step 4: Forces are ALWAYS equal magnitude, opposite direction!

Sentence Starters:

  • "The [animal] pushes [environment] [direction], so the [environment] pushes [animal] [opposite direction]."
  • "By Newton's Third Law, the forces are equal because..."

COMPLETE THE STATION 2 FORM BELOW

Identify force pairs in biological scenarios and solve the cheetah calculation.

[EMBED G8.C2.W3 Station 2 Form Here]

Form ID: ________________

Station 3 - Design a Force Pair System

25 Points | ~20 Minutes (Highest Value!)

Engineering Challenge: Design Your Own Newton's 3rd Law Demonstration

Your Mission:

Design a demonstration or device that clearly shows action-reaction force pairs using Newton's Third Law principles.

Possible Ideas:

  • Balloon rocket: Air pushes backward → balloon moves forward
  • Skateboard push: You push wall backward → wall pushes you forward
  • Water bottle rocket: Water sprays down → bottle flies up
  • Two-chair collision: Wheeled chairs push apart equally after collision

Your Design Must Include:

Component What to Include
Force Pair Identification Identify both action and reaction forces
Objects Identified State which object each force acts on
Equal-Opposite Explanation Explain why forces are equal magnitude
No Cancellation Explanation Explain why pairs don't cancel (different objects)
Acceleration Calculation If masses given, use a=F/m to calculate accelerations
Need extra support? Click here for design hints

Design Tips:

  • Choose a simple system with two clear objects (e.g., balloon + air, you + wall)
  • Identify BOTH forces in the pair (object A on B, object B on A)
  • Remember: Forces act on DIFFERENT objects, so they can't cancel
  • Use a=F/m to explain why lighter objects accelerate more

Sentence Starters:

  • "Object A exerts [force] on Object B, so Object B exerts [equal force] on Object A."
  • "These forces don't cancel because..."
  • "Even though the forces are equal, Object A accelerates more because it has less mass (a=F/m)."

COMPLETE THE STATION 3 FORM BELOW

Design your Newton's Third Law demonstration!

[EMBED G8.C2.W3 Station 3 Form Here]

Form ID: ________________

Exit Ticket - N3L Mastery + C3 Preview

23 Points | ~15 Minutes

Show What You Learned

Question Types:

  • 2 NEW - Newton's Third Law, force pairs, biological applications
  • 2 SPIRAL - Week 2 F=ma calculations (building connection!)
  • 1 INTEGRATION - C3 cheetah preview (F=ma + N3L combined)
  • 1 SEP-4 - Analyze collision data from PhET

C3 Bridge Question:

Your integration question will ask you to combine F=ma (W2) with N3L (W3) to analyze a cheetah-gazelle scenario. This prepares you for Cycle 3 predator-prey dynamics!

COMPLETE THE EXIT TICKET BELOW

This is your final assessment for Week 3. Take your time!

[EMBED G8.C2.W3 Exit Ticket Form Here]

Form ID: ________________

Enrichment & Extension
Optional deep dives for early finishers.

Optional content if you finish early or want to go deeper.

Scientist Spotlight

Research a scientist who contributed to this week's topic area and describe their key findings.

Environmental Justice Connection

Explore how this week's science concepts connect to environmental justice issues in our community.

↑ Back to Navigation