Static Electricity

Like winter static, rubbing two objects moves electrons so one side becomes (+) and the other (−). Before friction both are neutral; only electrons move, while protons stay fixed in the nucleus. Like charges repel and opposite charges attract, and an electroscope can show whether something is charged. Here you can watch electron transfer between a glass rod and cloth by friction.

Where Does Electricity Come From?

🧤 Winter Static — It's About Electron Transfer

①Rub a balloon on hair and the hair sticks to it

②Friction between two objects moves electrons (−) from one to the other

③The side that loses electrons becomes (+); the side that gains them becomes (−)

Charge Transfer by Friction

Electrons transferred3

💡 Core Principle

①Before friction: both objects have equal protons (+) and electrons (−), neutral

②Friction moves only electrons — protons are fixed in the nucleus

③Electrons-lost glass rod → (+); electrons-gained cloth → (−)

Forces Between Charges

Like charges → repel; opposite charges → attract

(+)/(+) and (−)/(−) → repel | (+)/(−) → attract

Charging & Electroscope

🔬 How an Electroscope Works

①Bring a charged object near the metal plate

②Like charges flow into the leaves

③The leaves spread apart — proof of charge!

Ways to Charge

Friction / Contact / Induction

Friction: rub to move electrons | Contact: touch the charged object | Induction: separation without contact

Summary

Static-Electricity Core

Friction → electron transfer → charging → electric force

Lose electrons → (+); gain electrons → (−)

🎯 Exam Key Points

①Only electrons (−) move during friction — protons (+) cannot move

②Like charges repel, opposites attract

③Uncharged objects have equal (+) and (−) (neutral)

④Spread leaves on an electroscope = charged

⑤Triboelectric series: glass > nylon > silk > ebonite > rubber

Examples and Unit Test

Example 1

After rubbing a glass rod with a cloth, the glass rod became positively charged. Which way did electrons move, and what charge does the cloth have?

When rubbed, electrons (negative) move from one object to another; the one that loses electrons becomes positive and the one that gains them becomes negative.

Since the glass rod became positive, electrons moved from the glass rod to the cloth, and the cloth that gained electrons has a negative charge.

▸ Electrons moved from the glass rod to the cloth / the cloth is negatively charged

In rubbing, losing electrons gives a positive charge and gaining electrons gives a negative charge.

Example 2

When two objects with the same negative charge are brought close, what force acts between them, and what force acts between a positive and a negative charge?

Between charges of the same kind, a repulsive force (pushing apart) acts.

Negative and negative are the same charge, so they repel; positive and negative are different charges, so an attractive force acts.

▸ Negative and negative = repulsion / positive and negative = attraction

Like charges push apart (repel); unlike charges pull together (attract).

Unit-test style

Which statement about the generation of electricity is correct?

①When rubbed, protons move to give a charge

②When rubbed, electrons move to give a charge

③Charges of the same kind attract each other

④An object that gains electrons becomes positively charged

⑤Charges of different kinds repel each other

▸ ② When rubbed, electrons move to give a charge