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# Where does static charge come from?

Year 9 Physics · Wave and particle models

<!-- Speaker note: 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 (Engage and Explore 8 min · Explain 10 min · Evaluate 3 min · Typical adds 3 min, Wider about 2 min). -->

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## Today

**We are learning to** 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.

- 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.

<!-- Speaker note: 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. Teacher: In your own words: the before and after atom diagrams. -->

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## Why it matters

> Pull a woolly jumper over your head in the dark and you can see tiny sparks. Where does a spark come from?

<!-- Speaker note: You know the balloon-and-hair trick. This lesson says what actually moved. -->

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<span style="background:#dbeafe; color:#1a1a1a; border:1.5px solid #3b82f6; padding:6px 18px; border-radius:8px; font-size:1em; font-weight:500;">💬 Discussion</span>

## Engage: predict

**You rub a balloon on wool, and now the balloon is charged. What moved from one to the other?**

- Protons, from one material to the other
- Whole atoms
- Electrons, from one material to the other
- Nothing moved: rubbing made new charge

<!-- Speaker note: What happens: Electrons. They are the only charges free to move. Protons are locked inside the nuclei. The material that gains electrons becomes negative; the one that loses them becomes positive. Take two or three predictions before anyone runs it. -->

<!-- Speaker note: Teacher: tally the predictions. Ask the 'protons' group why only electrons are free. -->

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<span style="background:#fef3c7; color:#1a1a1a; border:1.5px solid #f59e0b; padding:6px 18px; border-radius:8px; font-size:1em; font-weight:500;">✍️ Activity</span>

## Explore it

{{embed: https://studio.learningwaypoints.com/tutorials/_playground-board/index.html?id=deck%2Fscience%2Fphysics-9%2Fstatic-charge%2Fstep-2&code=widget%3A+charge%0Amode%3A+static%0Arub%3A+Wool+%3E+Balloon%0A&fresh=1}}

[Open this step in the tutorial](https://studio.learningwaypoints.com/tutorials/science/physics-9/static-charge/?full=step-2#step-2)

<!-- Speaker note:  -->

<!-- Speaker note: Teacher: ask what has to be true of the two net charges. -->

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<span style="background:#dcfce7; color:#1a1a1a; border:1.5px solid #22c55e; padding:6px 18px; border-radius:8px; font-size:1em; font-weight:500;">✅ Check</span>

## What happened?

* Electrons. They are the only charges free to move. Protons are locked inside the nuclei. The material that gains electrons becomes negative; the one that loses them becomes positive.

<!-- Speaker note: Reveal after running. Ask who predicted it, and what made them think so. -->

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<span style="background:#dcfce7; color:#1a1a1a; border:1.5px solid #22c55e; padding:6px 18px; border-radius:8px; font-size:1em; font-weight:500;">✅ Check</span>

## Why positive

**The wool ends up positively charged. Why?**

- It gained protons
- It lost electrons, so it has more + than − charge
- It made positive charge when rubbed

* Answer: It lost electrons, so it has more + than − charge

<!-- Speaker note: Losing negative electrons leaves a surplus of positive charge from the protons that stayed behind. -->

<!-- Speaker note: Teacher: electron transfer and the spark are the success criteria. -->

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<span style="background:#dcfce7; color:#1a1a1a; border:1.5px solid #22c55e; padding:6px 18px; border-radius:8px; font-size:1em; font-weight:500;">✅ Check</span>

## Equal and opposite

**The balloon gained 3 electrons from the wool. What is the wool's charge?**

- −3, the same as the balloon
- +3: it lost the 3 electrons the balloon gained
- 0, because charge cancels

* Answer: +3: it lost the 3 electrons the balloon gained

<!-- Speaker note: No charge is created or destroyed: the balloon's −3 is balanced by the wool's +3, so the total is still zero. -->

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<span style="background:#dcfce7; color:#1a1a1a; border:1.5px solid #22c55e; padding:6px 18px; border-radius:8px; font-size:1em; font-weight:500;">✅ Check</span>

## Attract or repel

**Do the two charged objects attract or repel?**

Groups: Attract · Repel

A positive and a negative · Two negatives · Two positives

* Answer: A positive and a negative → Attract; Two negatives → Repel; Two positives → Repel

<!-- Speaker note:  -->

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<span style="background:#dcfce7; color:#1a1a1a; border:1.5px solid #22c55e; padding:6px 18px; border-radius:8px; font-size:1em; font-weight:500;">✅ Check</span>

## A spark

**What is a spark, in terms of electrons?**

- Extra electrons rushing across to neutralise a charge imbalance
- Heat from friction
- Protons jumping across a gap

* Answer: Extra electrons rushing across to neutralise a charge imbalance

<!-- Speaker note: When the charge imbalance is big enough, electrons jump the gap all at once to even things out: a spark, or on a huge scale, lightning. -->

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<span style="background:#fef3c7; color:#1a1a1a; border:1.5px solid #f59e0b; padding:6px 18px; border-radius:8px; font-size:1em; font-weight:500;">✍️ Activity</span>

## Elaborate: push and pull

{{embed: https://studio.learningwaypoints.com/tutorials/_playground-board/index.html?id=deck%2Fscience%2Fphysics-9%2Fstatic-charge%2Fstep-4&code=widget%3A+charge%0Amode%3A+pair%0Afirst%3A+2%0Asecond%3A+-1%0A&fresh=1}}

[Open this step in the tutorial](https://studio.learningwaypoints.com/tutorials/science/physics-9/static-charge/?full=step-4#step-4)

<!-- Speaker note: What this step is for: Making the balls repel and attract with charges the student sets turns the rule into something they can predict and test. -->

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<span style="background:#dcfce7; color:#1a1a1a; border:1.5px solid #22c55e; padding:6px 18px; border-radius:8px; font-size:1em; font-weight:500;">✅ Check</span>

## Which feels more

**Ball 1 is +3 and ball 2 is +1. What happens, and which ball feels the bigger force?**

- They repel, and ball 1 feels more
- They repel, and the force on each is the same size
- They attract, and ball 1 feels more

* Answer: They repel, and the force on each is the same size

<!-- Speaker note: Like charges repel. The two forces are equal in size and opposite in direction, whatever the sizes of the charges. -->

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<span style="background:#dcfce7; color:#1a1a1a; border:1.5px solid #22c55e; padding:6px 18px; border-radius:8px; font-size:1em; font-weight:500;">✅ Check</span>

## Elaborate: lightning

**In a thunderstorm, ice and water particles rub past each other and charge builds up in the cloud. What is lightning?**

- Positive charge falling from the cloud
- A huge discharge: electrons rushing between the cloud and the ground (or another cloud) to neutralise the charge imbalance
- Heat energy escaping from the cloud

* Answer: A huge discharge: electrons rushing between the cloud and the ground (or another cloud) to neutralise the charge imbalance

<!-- Speaker note: It is the same idea as the spark from the balloon, with far more charge and a much longer path. What this step is for: Lightning applies electron transfer and discharge at a scale the student cannot reproduce. -->

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## 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.

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<span style="background:#dcfce7; color:#1a1a1a; border:1.5px solid #22c55e; padding:6px 18px; border-radius:8px; font-size:1em; font-weight:500;">✅ Check</span>

## Exit ticket

**A plastic ruler is rubbed on a cloth and becomes negative. What happened to the cloth, and why?**

* The cloth became positive. Electrons moved from the cloth to the ruler, so the cloth has more + than −.

<!-- Speaker note: Students answer on paper or a mini whiteboard before the reveal. Anyone who cannot answer needs the main idea again next lesson. Where this 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. -->