Everything is made of atoms with positive protons that stay put and negative electrons that can move. Rubbing two materials moves electrons from one to the other, leaving one positive and one negative. Opposite charges attract, like charges repel, and a spark is the extra electrons rushing back to even things out.
Pull a woolly jumper over your head in the dark and you can see tiny sparks. Where does a spark come from?
You know the balloon-and-hair trick. This lesson says what actually moved.
Engage: Commit to a prediction before you test anything. A wrong guess is fine: it shows you what to look for.
Explore: Try it on the board and compare what happens with your prediction.
Explain: Use the particle model to explain what you saw.
Elaborate: Use the same idea in a new context.
Evaluate: Look back at your first ideas and what changed.
WidthMore contexts, same idea.
Make your prediction first. Help opens once you've locked it in.
EngageCommit to a prediction before you test anything. A wrong guess is fine: it shows you what to look for.
Engage: the balloon
ExploreTry it on the board and compare what happens with your prediction.
Explore: rub and discharge
Each press moves one electron. Look at the atoms in the wool: which ones now show only a +?
Try it yourselfYour edits are saved in this browser.
Press Rub until the wool has charge +3. What does the balloon have?
Use the board. This ticks when you get there.
Rub a few times, then press Touch metal. Watch what happens to the charges.
Use the board. This ticks when you get there.
ExplainUse the particle model to explain what you saw.
Explain: charge and force
In your book: draw a neutral balloon and a neutral wool cloth as atoms with + and −. Then draw them after rubbing, with arrows showing which way the electrons went and the net charge of each.
Do the two charged objects attract or repel?
A positive and a negative
Two negativesLike charges repel.
Two positivesLike charges repel.
Elaborate TypicalUse the same idea in a new context.
Elaborate: push and pull
Try it yourselfYour edits are saved in this browser.
Set the charges so the balls push each other apart.
Use the board. This ticks when you get there.
Now make them pull together.
Use the board. This ticks when you get there.
Elaborate WiderUse the same idea in a new context.
Elaborate: lightning
EvaluateLook back at your first ideas and what changed.
Evaluate: look back
Write one sentence: "At first I thought… Now I think… because…"
Revision summary
Atoms have positive protons that stay put and negative electrons that can move.
Rubbing moves electrons from one material to the other: one becomes positive, the other negative, by equal amounts.
Unlike charges attract; like charges repel.
A spark is the extra electrons rushing across to neutralise the imbalance.
For teachers
Students explain static electricity as the transfer of electrons between materials that leaves a charge imbalance, and use it to explain attraction, repulsion and electrostatic discharge (AC9S9U04, node 3). About 24 minutes.
I can say what moves when two materials are rubbed together.
I can say which charges attract and which repel.
I can explain what a spark is.
Before class
A concept tutorial for introducing or revising the idea. Set the width with ?width=minimum, typical (default) or wider. It follows the sound lesson and comes before How does current flow?, which uses the same particle picture inside a wire.
Not a hinge node, but students carry two misconceptions here: that rubbing makes charge, and that protons move. The prediction targets both.
Board notes: eight atoms per material; one electron moves each time Rub is pressed (at most 6). Which material loses electrons depends on the pair; wool to balloon is a typical case. Charging by induction and by contact are left to class demonstrations.
Running the lesson
Engage: tally the predictions. Ask the 'protons' group why only electrons are free.
Explore: ask what has to be true of the two net charges.
Explain: electron transfer and the spark are the success criteria.
In your own words: the before and after atom diagrams.
The hard part (on purpose)
Charge is moved, not made, and only electrons move. When a student says the balloon 'got a positive charge from the wool', ask which particle would have had to cross.
When students get stuck
A student says the wool and the balloon are both negative. Ask: Where did the balloon's extra electrons come from? Fix: From the wool, which now has fewer electrons than protons, so it is positive.
A student says protons moved. Ask: Are protons free to leave the atom? Fix: No: they are locked in the nucleus. Only electrons can be rubbed off.
A student thinks a neutral object has no charges at all. Ask: How many + and − are in each atom? Fix: Equal numbers, so they cancel. Neutral means balanced, not empty.
Stretch and support
Stretch: A glass rod rubbed with silk becomes positive and the silk negative. Which material lost electrons? Which gained? (The rod lost; the silk gained.)
Support: Give a two-column table (Before rubbing, After rubbing) with the + and − counts for each material, and let students fill the after column by moving one − at a time.
Where it leads
Next: How does current flow? uses the same picture inside a metal wire.
In class: rub a balloon on hair and pick up paper bits; a comb or ruler and a thin stream of water; an electroscope or a Van de Graaff generator if available. Many materials charge better in dry air.
What each step is for
Engage: the balloon: Students say the balloon 'picks up' positive charge, or that charge is made by rubbing. Only electrons are free to move, and they come from somewhere.
Explore: rub and discharge: Watching one electron at a time leave the atoms of one material and arrive at the other makes 'charge by transfer' concrete, and shows the two net charges are equal and opposite.
Explain: charge and force: Explaining charging as electron transfer, then using it for attraction, repulsion and sparks, meets the node's first success criterion and its static-electricity application.
Elaborate: push and pull: Making the balls repel and attract with charges the student sets turns the rule into something they can predict and test.
Elaborate: lightning: Lightning applies electron transfer and discharge at a scale the student cannot reproduce.
Now you can
Say what moves when two materials are rubbed together.