Magnetic Forces, Fields & Distance · Grade 6 Science
Chapter: Electricity, Magnetism & LightMagnetic Forces, Fields & Distance
Learning goals
- I can name which materials are magnetic and design a test to check a sample.
- I can describe a magnetic field and how its strength changes with distance.
- I can explain how an electromagnet differs from a permanent magnet.
Readings for this unit
Before this unit
Read the chapter opening and the named observation or diagram. Clarify one word or unit that blocks understanding. Recall the relevant earlier measurement, matter, or energy idea.
Study the unit across three 35–45-minute class sessions. Use the worked examples after an attempt and the supplied records when actual equipment is not available.
Almost every student arrives believing that magnets attract metal. Test it and the belief collapses in under a minute: a magnet ignores aluminium foil, a copper coin, a gold ring and a stainless steel sink, and grabs an iron nail and a steel paperclip. The magnetic materials are iron, nickel and cobalt, together with alloys containing them, and that is essentially the whole list.
A magnet acts without touching, through a region around it called a magnetic field. Every magnet has two poles, north and south, and the familiar rule applies: like poles repel, unlike poles attract. Cut a magnet in half and you do not get a separate north and a separate south, you get two complete magnets, each with both poles.
The field weakens dramatically with distance. Double the gap between a small magnet and a paperclip and the force does not halve, it falls to roughly an eighth. That is why a fridge magnet holds firmly when touching the door and drops away if a sheet of card is slipped behind it.
Build your understanding
Where this fits
This lesson sits between charge and light in the chapter on forces that act at a distance. Magnetism shares its shape with electrostatics from two lessons ago, with poles in place of charges and the same attract and repel rule, and the field idea introduced here is the one that returns in chapter 8 when gravity holds planets in orbit across empty space.
Use three flexible 40-45-minute sessions: poles and which materials respond; the field and how it changes with distance; Earth as a magnet and how electromagnets work, then the practice set, revision and the exit check. Workshop, review, quiz and exams have separate time.
Part 1 · Which materials actually respond
The test is quick and settles the question better than any explanation. Collect a copper coin, a strip of aluminium foil, a steel paperclip, an iron nail, a piece of brass, a stainless steel spoon and some coins of mixed composition, then bring a magnet to each in turn. The paperclip and the nail jump to it. The copper, the aluminium and the brass do nothing whatever, and most stainless steel does nothing either, because the chromium and nickel in it are arranged in a way that suppresses the effect. A student who has done this once never again says that magnets attract metal, which is the point of doing it rather than being told.
The materials that do respond are iron, nickel and cobalt, plus steel and other alloys containing them, and the reason is worth a sentence even at this level. In these metals the atoms behave like tiny magnets themselves and can line up in large groups all pointing the same way, so their individual effects add together instead of cancelling. In copper or aluminium the atoms cannot line up like this, so no amount of stroking with a magnet will magnetise them. This also explains why heating a magnet strongly or dropping it hard can weaken it: the lined-up groups are jostled out of alignment and the effects start cancelling again.
Pause and explain
A student says magnets attract metal. Describe a test that disproves this and explain the result.
Check your reasoning after answering
Bring a magnet to a copper coin, aluminium foil and a brass object alongside an iron nail; only the nail is attracted. Copper, aluminium and brass are all metals and none of them respond, so being a metal is not what matters. The magnetic materials are iron, nickel and cobalt and alloys containing them, because only in those can the atoms line up so their effects add.
Part 2 · The field, and how fast it fades
A magnetic field is the region around a magnet where its force can be detected, and although it cannot be seen it can be mapped. Scatter iron filings on paper over a bar magnet and tap gently: each filing turns to line up with the field and the pattern that appears shows lines running out of the north pole, curving round and back into the south pole. A small plotting compass does the same job one point at a time and has the advantage of showing direction, since the needle always points along the field at that spot.
The strength falls off far faster than students expect, and measuring it is more convincing than being told. Hang a paperclip from a thread and find the distance at which a magnet just lifts it, then try again with the magnet twice as far away: the pull is not half as strong but roughly an eighth, because for a small bar magnet the force falls with the cube of the distance. This explains the everyday behaviour of magnets completely. It is why they must be touching or nearly touching to hold anything, why a fridge magnet fails with a few sheets of paper behind it, and why magnetic catches on cupboard doors are designed to close the gap to nothing. Put numbers on it and the fall is stark. A small neodymium magnet might pull a steel washer with a force of about 4 N when touching, around 0.5 N at 2 mm, and under 0.1 N at 5 mm, so across a gap narrower than a pencil lead the force drops to a fortieth. Nothing else in this course changes that fast with distance, and it is the single fact that explains how magnets get used.
Pause and explain
A magnet just lifts a paperclip at 1 cm. What happens at 2 cm, and why does this matter in everyday life?
Check your reasoning after answering
The force falls to roughly an eighth, not a half, because for a small bar magnet it drops with the cube of the distance. That is why magnets have to be in contact or nearly so to be useful, why a fridge magnet slides off with card behind it, and why magnetic catches are made to close the gap completely rather than nearly.
Part 3 · Earth is a magnet
A compass needle is a small magnet free to turn, and it settles pointing roughly north because Earth itself has a magnetic field, produced by the motion of liquid iron in its outer core. That field is weak compared with a classroom magnet, measuring between about 25 and 65 microtesla at the surface, which is why a compass needle has to be delicately mounted and why holding a fridge magnet near one swamps it instantly. The field still extends tens of thousands of kilometres into space, where it deflects charged particles from the Sun and produces the aurora near the poles. The contrast in strength is worth holding on to. Earth's field is roughly 50 microtesla in most inhabited places, while a small neodymium magnet of the kind used in headphones reaches about 500 mT at its surface, around ten thousand times greater. Earth's field wins only because it is everywhere and never switches off, which is exactly why it works for navigation and would be useless for lifting anything.
There is a confusing detail here that is worth getting straight rather than glossing over. The end of a compass needle that points north is a north pole, and unlike poles attract, so the magnetic pole in the Arctic is actually a magnetic south pole. Worse, it is not in the same place as the geographic North Pole and it moves: it has drifted hundreds of kilometres over the last century and currently shifts by tens of kilometres a year. Maps therefore print a correction, called declination, telling you how far a compass reading differs from true north at that place and in that year.
Pause and explain
Why does a map print a declination figure that changes from year to year?
Check your reasoning after answering
Because a compass points to the magnetic pole, which is neither at the geographic North Pole nor fixed in place. The magnetic pole is produced by moving liquid iron in Earth's core and drifts by tens of kilometres a year, so the angle between magnetic north and true north differs by location and changes over time, and navigation needs the correction for that place and date.
Part 4 · Magnetism you can switch off
A current flowing in a wire produces a magnetic field around it, and winding that wire into a coil around an iron core concentrates the effect into an electromagnet. The crucial difference from a bar magnet is control: the field exists only while current flows, so it can be switched on and off, and its strength can be varied by changing the current or the number of turns in the coil. Reversing the current reverses the poles, which a permanent magnet cannot do at all.
That controllability is why electromagnets do most of the useful work. A scrapyard crane lifts a tonne of steel and releases it by opening a switch, which no permanent magnet could manage. A doorbell works by an electromagnet pulling a striker against a spring, breaking its own circuit as it moves, springing back and starting again many times a second. Electric motors, loudspeakers, hard disk drives and the relay in a car starter all depend on a magnetic field that can be created, reversed and removed on demand. The strengths available go far beyond anything a permanent magnet of the same size could manage. A scrapyard electromagnet lifts several tonnes, and a hospital MRI scanner runs at about 1.5 tesla, roughly thirty thousand times Earth's 50 microtesla and strong enough that a steel oxygen cylinder brought into the room becomes a lethal projectile. That is why MRI rooms are controlled so strictly.
Pause and explain
Why does a scrapyard crane use an electromagnet rather than a very strong permanent magnet?
Check your reasoning after answering
Because it has to let go. A permanent magnet's field cannot be turned off, so the steel could not be released at the destination, while an electromagnet's field exists only while current flows and disappears when a switch is opened. The strength can also be adjusted by changing the current, which a permanent magnet does not allow.
Apply the whole unit · Design the sorting test
A recycling centre receives a mixed load of drinks cans, some aluminium and some steel, along with copper wire offcuts. A magnet on a moving belt is proposed to separate them.
Your task
Predict what the magnet will separate, explain why, and identify what the method cannot do.
What your response should show
- Identifies steel as magnetic and aluminium and copper as not, with the reason
- Uses the rapid fall-off with distance to justify placing the magnet close
- Names a pair the magnet cannot separate
- Proposes a different property with figures that would separate them
Response guidance — after your attempt
State which items the magnet will lift and which it will leave, with the reason.
Explain why the magnet must be close to the belt, using what you know about distance.
Name one thing this method cannot separate and suggest a property that would.
The magnet will lift the steel cans, because steel is an iron alloy and iron is one of the three magnetic metals. It will leave the aluminium cans and the copper wire, since neither metal responds to a magnet at all, which is the point of the method: it sorts by a property rather than by appearance, and steel and aluminium cans look almost identical. The magnet has to run close to the belt because magnetic force falls with roughly the cube of the distance, so a magnet at 4 cm exerts about an eighth of the pull it would at 2 cm, and cans at the bottom of a deep layer would simply be missed. What the method cannot do is separate the aluminium from the copper, since neither is magnetic. Density would work instead, since aluminium is about 2.70 g/cm3 and copper about 8.96 g/cm3, so the two behave very differently in a water or air separator.
Scientific references for this unit
- National Oceanic and Atmospheric Administration: Earth's magnetic field and declination
- US Geological Survey: the geomagnetic field and why the poles move
- Institute of Physics: magnets, fields and electromagnets in the classroom
- US Environmental Protection Agency: how recycling plants sort metals
Parent / teacher teaching notes
Begin with the literal observation, quantity, or diagram relationship. Ask the learner to explain why the evidence supports the claim, check a relevant unit or boundary, then discuss an alternative. The supplied numbers are illustrative, not real observations. A parent can read aloud and allow a spoken rehearsal before writing. Judge science and evidence rather than political, faith, or family agreement. Use the complete data option whenever an actual procedure is unavailable or unsuitable.
The key idea
Only a handful of materials are magnetic, and the common belief that all metals are is wrong and easy to disprove. A magnet acts through a field whose strength falls away extremely quickly with distance, which is why magnets must almost touch to be useful.
Worked examples
Example 1 · Interpret a distance record
- Keep count distinct from measured force.
- Describe the ordered-distance pattern.
- Average the repeat counts and state a limit.
Example 2 · Transfer to a different case
- Identify the distinction and conditions in this new case.
- Use the relevant mechanism or quantity; preserve units and the chosen boundary.
- Explain why the answer fits and what further evidence would be needed.
Example 3 · Interpret a magnetic field model · a focused example
- State the literal condition or observation in the example.
- Apply the distinction explained in this teaching part.
- Check whether the claim stays within the given evidence.
Avoid these mistakes
- Misleading claim: Every metal must be strongly attracted by a magnet.
- Misleading claim: Dividing a bar magnet creates an ordinary magnet with only one pole.
- Omitting units, measurement timing, or a model boundary makes the evidence hard to interpret.
- Treating illustrative classroom data as real field measurements or copying a model is not an independent explanation.
Check your understanding
Are magnetic north and electric positive the same label?
Discuss the answer
No. They belong to different models; magnetic pole labels are not net electric charge labels.
Why can a nearby magnet affect a compass?
Discuss the answer
It contributes to the local magnetic field with which the compass aligns.
Does no visible movement prove the field is exactly zero?
Discuss the answer
No. The force may be too small to overcome friction or be detected by the procedure.
What does that record support?
Discuss the answer
A current-associated magnetic effect in the stated setup, with its detection limits; it does not establish every current strength or construction.
Sustained scientific explanation and revision
These activities are scheduled in the parent plan. Save a first response, a correction, and the reason for the change in the science notebook.
Activity 1 · Magnetic Forces, Fields & Distance · Model and explain
Read A Reading Lamp Is More Than a Bright Object and the linked unit teaching; use its complete supplied case and diagrams.
Your task
For Magnetic Forces, Fields & Distance, study Parts 3–4 and attempt the worked case: Describe the pattern and repeat variation without inventing a precise force law. Explain the steps before opening the model.
Success criteria
- An accurate scientific claim answering the actual question.
- Relevant evidence or a labeled model with quantities and units when applicable.
- Reasoning that connects evidence with the mechanism rather than only repeats it.
- A specific method, boundary, scale, or alternative-explanation limit.
Hint
Begin with the actual observation, quantity, or diagram relationship. Explain how it bears on the question before making a broad claim.
Response guidance — discuss after your attempt
The recorded holding count decreases as gap increases under this method. At 2 cm the mean is 5 clips and the range 4–6. Clip count is a practical proxy, not force in newtons, and these three distances do not establish an exact mathematical law or prove the field stops beyond 3 cm.
Activity 2 · Magnetic Forces, Fields & Distance · Practice, revise and exit
Read A Reading Lamp Is More Than a Bright Object and the linked unit teaching; use its complete supplied case and diagrams.
Your task
For Magnetic Forces, Fields & Distance, complete practice questions 1–6 and both choice checks, then answer independently: A magnet attracts one metal washer but not another. Is the second washer necessarily nonmetal? Save a correction explaining one changed claim or method.
Success criteria
- An accurate scientific claim answering the actual question.
- Relevant evidence or a labeled model with quantities and units when applicable.
- Reasoning that connects evidence with the mechanism rather than only repeats it.
- A specific method, boundary, scale, or alternative-explanation limit.
Hint
Begin with the actual observation, quantity, or diagram relationship. Explain how it bears on the question before making a broad claim.
Response guidance — discuss after your attempt
No. Metals differ in magnetic response, and the method has limits. Attraction is not a universal test for all metal identity.
Words to know
- magnetic field
- A representation of magnetic interaction around magnets or electric currents.
- pole
- A north or south magnetic orientation region in the simple magnet model.
- evidence
- A relevant observation, measurement, or record used to evaluate a claim.
- system boundary
- The chosen limit specifying what is included and which exchanges cross it.
- uncertainty
- A stated limit in measurement or knowledge, distinct from a careless mistake.
In the real world
Exit check
A magnet attracts one metal washer but not another. Is the second washer necessarily nonmetal?
Check your explanation after answering
No. Metals differ in magnetic response, and the method has limits. Attraction is not a universal test for all metal identity.
Explain your reasoning without notes. If a key idea is missing, revisit the lesson and try again.