Electric Charge, Attraction & Materials · Grade 6 Science
Chapter: Electricity, Magnetism & LightElectric Charge, Attraction & Materials
Learning goals
- I can explain what happens to electrons when two materials are rubbed together.
- I can predict whether two charged objects attract or repel.
- I can explain why a charged balloon sticks to an uncharged wall.
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.
Rub a balloon on your hair and it will pick up small pieces of paper, stick to a wall, and make your hair stand up. Nothing has been created in the rubbing. Electrons have been scraped off your hair onto the balloon's surface, leaving the balloon with a surplus of negative charge and your hair with a shortage.
Charge comes in two kinds, called positive and negative, and the rule is short: like charges repel, unlike charges attract. Your hairs all lost electrons, so they all carry the same kind of charge and push each other apart, which is exactly what standing on end looks like.
Protons never move in any of this. They sit locked in the nuclei of atoms, and every example of static electricity in this lesson is electrons shifting from one place to another and then staying there until something lets them drain away.
Build your understanding
Where this fits
This chapter covers electricity, magnetism and light, and it starts with charge because circuits in the next lesson are charge in motion. The important move here is from describing what you see, a balloon sticking to a wall, to explaining it with something you cannot see, which is the skill chapter 1 called building a model.
Use three flexible 40-45-minute sessions: the two kinds of charge and the attraction rule; charging by friction and what actually moves; attraction without charging, and conductors against insulators, then the practice set, revision and the exit check. Workshop, review, quiz and exams have separate time.
Part 1 · Two kinds, and one rule
The evidence for two kinds of charge rather than one comes from a simple pair of observations. Rub two plastic rods with the same cloth, hang one from a thread and bring the other close: they push each other apart. Rub a glass rod with silk and bring it near the hanging plastic rod and the two pull together. One kind of charge cannot produce both results, so there must be two, and the names positive and negative were assigned by convention long before anyone knew what was moving. The rule that follows is that like charges repel and unlike charges attract, and the force grows rapidly as the objects come closer.
The scale of these forces is easy to underestimate because static effects look feeble. A balloon stuck to a ceiling carries perhaps a hundred-billionth of a coulomb of charge, an almost absurdly small quantity, and it is still enough to hold the balloon's whole weight against gravity. Scale the charge up and the effects become violent: a lightning strike moves something like 15 C in a few thousandths of a second, with a current around 30,000 A and a channel heated to roughly 30,000 degrees Celsius, which is about five times the surface temperature of the Sun. Between those two extremes sits the shock you get from a car door, which typically involves a few thousand volts but a current lasting well under a thousandth of a second. Voltage alone is a poor guide to danger, which is why a 3000 V static spark startles you and a 230 V mains socket can kill: what matters is how much charge keeps flowing and for how long.
Pause and explain
What observation shows that there must be two kinds of charge rather than one?
Check your reasoning after answering
That charged objects sometimes repel and sometimes attract. Two plastic rods rubbed with the same cloth push apart, while a rubbed glass rod pulls a rubbed plastic rod towards it. A single kind of charge could only ever produce one of those behaviours, so at least two kinds must exist, with like repelling and unlike attracting.
Part 2 · Rubbing moves electrons
When two surfaces are rubbed together, electrons are transferred from one to the other, and which direction they go depends on the pair of materials. Hair gives up electrons readily and polythene holds on to them, so rubbing a balloon on hair leaves the balloon negative and the hair positive. Rub glass with silk and the glass loses electrons instead, leaving it positive. Materials can be ranked in order of how strongly they hold electrons, and that ranking predicts the outcome for any pair.
Two details catch students out. The first is that nothing is created: the total charge of balloon and hair together is exactly what it was before, which is conservation of charge, an idea with the same shape as conservation of mass from chapter 2. The second is that only electrons move; protons stay in the nucleus. A material that becomes positively charged has not gained protons, it has lost electrons, and getting this the right way round matters because every later explanation in this chapter depends on it. The ranking itself is worth seeing once. Running from materials that give up electrons most readily to those that hold on hardest, a typical order is hair, glass, wool, cotton, paper, rubber, polythene and PTFE. Any two of these rubbed together leave the one earlier in the list positive and the later one negative, which is why a polythene balloon on hair works so reliably while two sheets of paper rubbed together do almost nothing.
Pause and explain
A glass rod rubbed with silk becomes positively charged. What has actually happened?
Check your reasoning after answering
The glass has lost electrons to the silk. Positive charge means a shortage of electrons, not an arrival of protons, which stay locked in the nuclei throughout. The silk has gained exactly the electrons the glass lost, so the total charge of the two together is unchanged, as conservation of charge requires.
Part 3 · Attracting something that is not charged
A wall is not charged, and a charged balloon still sticks to it. The explanation is polarization. The balloon's negative surface repels electrons in the part of the wall nearest it, pushing them slightly further away within their own atoms and molecules. That leaves the wall's surface facing the balloon very slightly positive and the region just behind it very slightly negative. Since the positive part is closer to the balloon than the negative part, and the force grows as distance shrinks, the attraction wins and the balloon stays put.
The same polarization explains the paper trick and several others. Small pieces of paper, a thin stream of water from a tap, and dust on a television screen all respond to a charged object without carrying any net charge themselves. It is a useful example of a model earning its keep: nothing about the paper looks different before and after, and the only evidence for the rearrangement inside it is that the prediction, that neutral objects will be attracted and never repelled, holds every single time. It is also why the attraction is temporary in a particular way. Hold the balloon against the wall and it stays for minutes or hours; bring a charged object near a conductor and the effect disappears the instant the charge drains away. A balloon will not stick to a metal radiator in the way it sticks to plaster, and that difference is the next section.
Pause and explain
A charged balloon attracts a neutral piece of paper. Why does the attraction win if the paper has no net charge?
Check your reasoning after answering
Because polarization separates the paper's charges slightly. The balloon's charge pushes like charges in the paper away and pulls unlike charges nearer, so the side facing the balloon carries the opposite charge and the far side the same charge. The attracting charges are closer than the repelling ones, and the force is stronger at shorter distance, so attraction wins.
Part 4 · Where the charge goes
Materials differ in whether charge can move through them. In a conductor, typically a metal, some electrons are free to travel through the whole material, so any excess charge spreads out immediately and drains away to earth at the first opportunity. In an insulator such as plastic, rubber, glass or dry wood, electrons stay where they are put, which is why charge builds up on these materials and stays long enough to do something noticeable.
This explains a pattern you can check against your own experience. Static shocks are common in winter and rare in humid summer weather, because damp air carries a thin film of moisture on every surface that conducts charge away as fast as it builds. It is why you get a shock from a car door after sliding across a synthetic seat but not from a wooden bench, and why aircraft refuelling and operating theatres use conducting floors and bonding cables on purpose: in those places a spark from accumulated charge is a genuine hazard rather than a nuisance. Earthing is the deliberate version of the same idea. Connecting an object to the ground with a conductor gives accumulated charge a path away, and the Earth is large enough to absorb any amount without becoming noticeably charged itself. A lightning conductor on a building is nothing more elaborate than a very good path to earth, offering the charge an easier route than through the brickwork.
Pause and explain
Why are static shocks far more common in winter than in humid weather?
Check your reasoning after answering
Because damp air leaves a thin film of moisture on surfaces, and that film conducts charge away as fast as rubbing can build it up. In cold dry conditions the air and surfaces are effectively insulating, so electrons transferred by friction stay in place and accumulate until there is enough to jump as a spark.
Apply the whole unit · Explain three observations
A student rubs a plastic ruler on a wool jumper. The ruler then picks up small pieces of paper, bends a thin stream of water from a tap, and pushes away a second ruler that was rubbed the same way.
Your task
Explain all three observations using charge, and say which one is evidence for polarization.
What your response should show
- States that electrons moved and names the resulting charge on each object
- Uses the like-repel rule to explain the two rulers
- Explains polarization in terms of charges separating within a neutral object
- Gives the never-repelled prediction as the test of the explanation
Response guidance — after your attempt
Say what moved during the rubbing and what charge each object ends up with.
Explain why the two rulers repel but the paper and water are attracted.
Identify which observation shows polarization and state the prediction that confirms it.
Rubbing transferred electrons from the wool to the plastic, since wool holds electrons less tightly, so the ruler is left negatively charged and the jumper positively charged, with the total unchanged. The two rulers repel because both were rubbed the same way and therefore carry the same kind of charge, and like charges repel. The paper and the water are not charged at all, so they must be attracted by polarization: the ruler's negative charge pushes electrons within each piece of paper slightly away, leaving the near face positive, and since the near face is closer than the pushed-back negative region the attraction exceeds the repulsion. The water stream bends for the same reason. The polarization evidence is the attraction of uncharged objects, and the prediction that confirms it is that neutral objects are always attracted and never repelled, whichever kind of charge the ruler happens to carry.
Scientific references for this unit
- National Oceanic and Atmospheric Administration: lightning, charge separation and currents
- Institute of Physics: electrostatics and charging by friction
- National Institute of Standards and Technology: electrostatic discharge and why it is controlled
- US Occupational Safety and Health Administration: static electricity hazards and bonding
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
There are two kinds of electric charge, and rubbing two materials together does not create either one: it moves electrons from one surface to the other, leaving one short and one with a surplus. A charged object can attract something uncharged, and the reason is worth understanding properly.
Worked examples
Example 1 · A conserved charge-transfer model
- Keep each object’s positive units unchanged.
- Transfer negative units rather than invent them.
- Compare both objects and the combined total.
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 · Explain interaction without contact · 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: Rubbing creates electric charge from nothing.
- Misleading claim: Attraction always proves two objects have opposite net charges.
- 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
Does losing electrons make the object negative?
Discuss the answer
No. It leaves more positive than negative charge in the stated model, so its net charge becomes positive.
Can repulsion occur without touching?
Discuss the answer
Yes. Electric interaction acts through a field; contact is not required for the modeled force.
Does attraction uniquely identify the paper’s net charge?
Discuss the answer
No. A shifted distribution in neutral material can also produce attraction; additional evidence is needed.
Why should handling be recorded?
Discuss the answer
It can affect charge movement and the observed interaction, so a difference cannot be assigned to material alone without comparable conditions.
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 · Electric Charge, Attraction & Materials · 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 Electric Charge, Attraction & Materials, study Parts 3–4 and attempt the worked case: Find each net imbalance and explain the total charge account. 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
A has ten positive and eight negative units, a net positive two. B has ten positive and twelve negative, a net negative two. The combined twenty positive and twenty negative units remain; charge is transferred, not created. These are model units, not measured coulombs or a rule for every rubbed material.
Activity 2 · Electric Charge, Attraction & Materials · 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 Electric Charge, Attraction & Materials, complete practice questions 1–6 and both choice checks, then answer independently: A charged object attracts a neutral water stream in a supplied model. Must the stream have acquired an opposite net charge? 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. Polarization can shift the interaction without requiring an opposite total net charge. Explain the modeled distribution rather than infer net charge from attraction alone.
Words to know
- net charge
- The imbalance between positive and negative charge in the chosen system.
- conductor
- A material in which charge can move relatively readily under stated conditions.
- 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 charged object attracts a neutral water stream in a supplied model. Must the stream have acquired an opposite net charge?
Check your explanation after answering
No. Polarization can shift the interaction without requiring an opposite total net charge. Explain the modeled distribution rather than infer net charge from attraction alone.
Explain your reasoning without notes. If a key idea is missing, revisit the lesson and try again.