Week 1: Magnetic Forces & Fields

Grade 8 Science | Rosche

MS-PS2-3 Forces and Interactions

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The Phenomenon: The Invisible Force Mystery

Anchoring Context & Focus Question

Why do some magnets attract through tables while others don't?

Magnetic field line patterns around a bar magnet showing dense lines near poles and sparse lines far away
Magnetic field lines curve from North to South pole. Denser lines = stronger force.
Magnetic field visualization around a cylindrical magnet
The invisible magnetic field extends in all directions around a magnet — not just at the poles! Wikimedia Commons

Before We Begin: Activate Your Prior Knowledge

Think back to Cycle 5: You learned how waves travel through materials — some pass through (transmission), some bounce back (reflection), some get absorbed. Now ask yourself: Magnetic forces also act through solid materials like wood and glass. Is a magnetic field a kind of wave? How can a force reach across empty space without anything touching? Keep this question in mind as you investigate today.

Hold a strong magnet above a wooden table. Slowly slide another magnet underneath. At some point, the top magnet jumps or spins — the force acts right through solid wood!

  • A strong neodymium magnet can attract a paperclip through a thick textbook.
  • A weak refrigerator magnet barely holds a single sheet of paper.
  • Two magnets can repel so strongly they fly apart — or attract so strongly you can't pull them apart.
  • Distance matters enormously — move just a centimeter away and the force drops dramatically.

St. Louis Connection

The Gateway Arch uses over 900 tons of steel — a magnetic material. During construction, workers had to account for Earth's magnetic field when using compass-based surveying instruments near all that steel. St. Louis is also home to Sigma-Aldrich, a major supplier of rare-earth magnetic materials used in MRI machines, electric vehicles, and wind turbines worldwide.

Why This Matters to YOU

Every electric motor — in your phone's vibration, your fan, your car — works because of magnetic forces. Understanding how distance and pole orientation affect force strength is the foundation of electrical engineering, one of the highest-paying career paths in STEM.

Focus Question: Why do some magnets attract through tables while others don't — and why does distance matter so much?

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

  • Describe magnetic fields and how they extend through space.
  • Explain how distance affects magnetic force strength (inverse relationship).
  • Identify factors that influence magnetic field strength.
  • Design an investigation to test magnetic force relationships.
NGSS 3D Standards

This Week's Standards

MS-PS2-3: Ask questions about data to determine the factors that affect the strength of electric and magnetic forces.

Spiral Standards (Review)

  • MS-PS4-2: Wave behavior through materials (Cycle 5)
  • MS-LS2-3: Energy flow in ecosystems (Cycle 4)
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
magnetic field campo magnético Region around a magnet where magnetic force acts
field lines líneas de campo Imaginary lines showing field direction and strength
poles polos The north and south ends of a magnet where the field is strongest
repulsion repulsión Force that pushes objects apart (like poles repel)
attraction atracción Force that pulls objects together (opposite poles attract)
inverse relationship relación inversa When one value increases, another decreases (force vs. distance)
levitation levitación Object floating using magnetic forces to counteract gravity

Hook – The Invisible Force Mystery

Observe magnetic field effects through various materials.

The Challenge

What You'll Do

  1. Watch the magnet-through-the-table demonstration
  2. Make predictions about WHY distance affects magnetic force
  3. Connect to Cycle 5: Do magnetic fields behave like waves?
  4. Answer diagnostic questions about field concepts

The Mystery Data

Your teacher holds a strong magnet above a table and measures how far below a paperclip jumps up:

Magnet TypeAttracts Through Paper?Through Textbook?Through Table?
Weak fridge magnetBarelyNoNo
Small neodymiumYesYesNo
Large neodymiumYesYesYes!

Key Question: The table is the same thickness for all three magnets. Why can the large neodymium attract through it but the fridge magnet can't even get through paper?

Stop & Think

Before you open the form below, formulate your hypothesis: If distance weakens all magnetic forces, what must be DIFFERENT about a strong magnet's field compared to a weak one?

Need a hint to check your thinking?
Think about field lines. A stronger magnet has MORE field lines packed into the same space. Even at a distance, those dense lines still have enough "reach" to pull a paperclip. A weak magnet's sparse field fades out before it gets through the table.
COMPLETE THE HOOK FORM

Observe and question factors affecting magnetic force.

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Worked Example and Simulation – Mapping Magnetic Field Lines

The Problem

Scenario: You place a compass near a bar magnet. The compass needle always points toward the magnet's south pole. You move the compass to different positions around the magnet and record which way the needle points at each location. Use your observations to map the magnetic field.

Iron filings showing magnetic field lines around a bar magnet
Iron filings reveal the invisible magnetic field around a bar magnet. Notice how lines are densest near the poles! Wikimedia Commons
Common Mistake — Read Before Solving

WRONG: "WRONG: "Magnetic fields only exist at the north and south poles of a magnet.""

RIGHT: "RIGHT:"

Step-by-Step Solution

Step 1: Place compass near the North pole

"The compass needle points AWAY from the N pole. This means the field direction at this point goes outward from North."

Step 2: Place compass near the South pole

"The compass needle points TOWARD the S pole. The field lines enter the magnet at South. So the pattern is: exit N → curve through space → enter S."

Step 3: Move the compass far from the magnet

"Far away, the compass barely responds — the field is very weak here. The field lines are spread out (low density = weak force)."

Now YOU Complete Steps 4-5:

Step 4: What happens when you place the compass between two magnets with N-N facing each other (repelling)? How do the field lines between them differ from N-S (attracting)?

Step 5: If field lines NEVER cross, what does this tell us about the direction of force at any point in space?

Fading Support: Steps 4 and 5 are YOUR turn. This builds your field-mapping skills before Station 1.

Now map the field yourself — Magnetic Field Simulator

Place compasses around different magnet configurations (single bar, N-S attracting, N-N repelling) and observe the field-line patterns. Use the data to answer Station 1's prediction questions.

Your Simulation Summary
Your prediction: —
Trial results: —
Average result: —
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Station 1 – Magnetic Field Mapping

Visualize fields using iron filings and compass arrays.
Magnetic field line patterns around a bar magnet
Field lines exit the North pole and enter the South pole. Denser lines = stronger field. Lines NEVER cross.

Your Mission: Visualize the Invisible

What to Observe with Iron Filings & Compass

ConfigurationField PatternWhere Densest?
Single bar magnetLines curve from N → SNear the poles
Two attracting (N-S)Lines connect between polesBetween the magnets
Two repelling (N-N)Lines push apart, compressSides of gap
PhET Simulation: Magnets and Electromagnets

Explore the simulation: Open PhET Magnet Simulation

  • Observe field line patterns around bar magnets
  • Move the compass around — watch the needle follow the field
  • Flip the magnet and see how the field reverses
  • Bring two magnets together — N-S vs N-N

Tip: Follow the POE Protocol — Predict before you start, Observe the patterns, then Explain why!

Hints & Sentence Starters

Key Concept Reminders:

  • Field lines show DIRECTION (N→S outside the magnet)
  • Denser lines = STRONGER field = MORE force
  • Lines NEVER cross (force has one direction at each point)
  • The field extends in ALL directions — not just at the poles

Sentence Starters:

  • "The field lines are densest near ___ which means..."
  • "When two N poles face each other, the lines..."
  • "The compass needle points ___ because the field direction is..."
Step-by-Step Help

Try these steps in order:

  1. Start with the PhET simulation — flip the magnet and watch field lines reverse
  2. Place the compass at the N pole — which way does the needle point?
  3. Move the compass to the S pole — does the needle reverse?
  4. Move the compass far from the magnet — does the needle respond weakly or strongly?

Phenomenon Check-In

Think back to the magnet-through-the-table demonstration. Now that you've mapped field lines, why does a strong neodymium magnet attract through a thick table while a fridge magnet can't even get through paper?

Need a hint to check your thinking?
A neodymium magnet has FAR more field lines packed tightly together. Even at the distance of a table's thickness, those dense lines still carry enough force to move a paperclip. A fridge magnet's sparse field fades to nearly zero after just a few millimeters.
COMPLETE THE STATION 1 FORM

Map and analyze magnetic field patterns.

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Station 2 – Force-Distance Investigation

Quantify inverse relationship and graph data.
Graph showing magnetic force decreasing rapidly with distance
The inverse relationship: force drops by ~4× every time distance doubles. This is NOT a straight line!

Your Mission: Measure the Invisible Force

Force vs. Distance Data (Spring Scale Measurements)

Distance (cm)Force (N)What Happened?
0.5 cm4.0 NVery strong — hard to separate
1.0 cm1.0 NDoubled distance → force ÷ 4
2.0 cm0.25 NDoubled again → force ÷ 4 again
4.0 cm0.06 NBarely detectable
8.0 cm0.015 NNearly zero
Hints & Sentence Starters

Key Pattern:

  • When distance DOUBLES, force drops by ~4× (not 2×)
  • This is called an inverse square relationship
  • The graph is a CURVE, not a straight line

Sentence Starters:

  • "When distance doubled from 1 to 2 cm, force changed from ___ to ___..."
  • "The graph shape is a curve because..."
  • "Refrigerator magnets only work close up because..."
Step-by-Step Help

Try these steps in order:

  1. Look at the data table — compare 0.5 cm (4.0 N) to 1.0 cm (1.0 N). How much did force drop?
  2. Now compare 1.0 cm to 2.0 cm. Same pattern?
  3. If distance doubles from 8→16 cm, predict: 0.015 ÷ 4 = ?

Stop & Think

Why do you think refrigerator magnets only work when touching the fridge? Use the data table to support your answer.

Need a hint to check your thinking?
Fridge magnets are WEAK ceramic magnets. At 0.5 cm they might only produce 0.1 N. By the inverse square pattern, at just 1 cm that drops to 0.025 N — not enough to hold anything. So they must be touching (essentially 0 cm gap) to work.
COMPLETE THE STATION 2 FORM

Measure and graph how magnetic force changes with distance.

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Station 3 – Design a Magnetic Levitation Device

Apply force understanding to engineering challenge.
Diagram of magnetic levitation system using repelling magnets with guide rails
Like poles repel — but keeping a floating magnet stable requires guide rails or active feedback. This is the core challenge of maglev engineering!

Engineering Challenge: Magnetic Levitation Display

Design Requirements & Constraints

RequirementDetailsPhysics Connection
Levitation height≥ 1 cm above baseForce-distance: need enough repulsion at 1 cm
StabilityObject doesn't flip or fallEarnshaw's Theorem: need guides
MechanismMagnetic repulsion onlyLike poles (N-N or S-S) facing
Object mass~50 gramsRepulsion force must exceed gravity

The Stability Problem (Earnshaw's Theorem)

In 1842, Samuel Earnshaw proved mathematically that static magnets alone cannot achieve stable levitation. The floating magnet will always want to flip or slide sideways. Real solutions: (1) physical guide rails or walls, (2) spinning the magnet (gyroscopic stability), or (3) electromagnets with feedback sensors (how real maglev trains work!).

Design Hints
📌 CER SCAFFOLD — Build your response in this order:
▶ CLAIM

Design Strategy:

  • Magnet choice: Neodymium (strong) for base; must overcome gravity at 1+ cm
  • Orientation: N-up on base, N-down on floating object
  • Stability fix: Guide rails, walls, or a central pole to prevent flipping

Sentence Starters:

  • "My design uses ___ magnets because the force at 1 cm needs to be..."
  • "I solved the stability problem by..."
  • "The force-distance relationship matters because..."

Stop & Think

Real maglev trains in Shanghai travel at 430 km/h. Why can't they use permanent magnets like your design? What advantage do electromagnets provide?

Need a hint to check your thinking?
Electromagnets can be turned on/off and their strength adjusted instantly by changing the electric current. Sensors detect the gap distance hundreds of times per second and adjust the current to maintain a stable hover. Permanent magnets can't do this — their strength is fixed.
COMPLETE THE STATION 3 FORM

Design a device that uses magnetic repulsion to levitate.

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Exit Ticket – Magnetic Force Integration

Synthesize understanding of magnetic forces and field behavior.

Show What You Learned

Question Types:

  • 2 NEW — Magnetic fields and force-distance relationship (this week)
  • 2 SPIRAL — Cycle 5 wave-material interactions + Cycle 4 energy flow review
  • 1 INTEGRATION + SEP-1 — Ask a testable question connecting magnetic forces to a real-world scenario

Stop & Think

Before starting the exit ticket, review: What is the relationship between field line density and force strength? What happens to force when distance doubles?

Need a hint to check your thinking?
Denser field lines = stronger force. When distance doubles, force drops by ~4× (inverse square). The field extends in all directions around the magnet, not just at the poles.
AUTONOMY SUPPORT: How to Ace the Exit Ticket

The Exit Ticket tests INTEGRATION — connecting ideas across weeks:

  • This Week: Magnetic fields extend through space; force decreases with distance (inverse square).
  • Cycle 5 Connection: Both waves and fields act at a distance through materials.
  • Cycle 4 Connection: Energy decreases from source — just like force decreases from a magnet.
COMPLETE THE EXIT TICKET

Demonstrate mastery of magnetic force concepts.

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Enrichment & Extension
Optional content if you finish early or want to go deeper.
Nikola Tesla with his electromagnetic equipment

Scientist Spotlight: Nikola Tesla

Nikola Tesla (1856–1943) was a Serbian-American inventor who revolutionized our understanding of magnetic fields and electromagnetic forces. He invented the alternating current (AC) motor by discovering how rotating magnetic fields could spin a metal rotor — the exact force-distance principles you explored today. The unit of magnetic field strength (the Tesla, T) is named after him. Every electric motor in your home uses his invention.

Environmental Justice: Rare Earth Mining

The neodymium magnets you used today contain rare earth elements mined primarily in China and the Democratic Republic of Congo. Mining these materials causes significant environmental damage — toxic waste ponds, deforestation, and water contamination that disproportionately affects Indigenous communities and low-income populations near mine sites. As demand grows for electric vehicles and wind turbines (which rely on powerful magnets), understanding the physics helps us design motors that use LESS rare earth material, reducing the human and environmental cost.

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Week 1 Complete!

Next Week: Electromagnetism & Energy Transfer — how can spinning a magnet create electricity?