Like winter static, rubbing two objects moves electrons to one side, so one becomes (+) and the other (−).
Before the rub both are neutral; only electrons change place, and protons stay fixed in the nucleus.
Like charges push apart and opposite charges pull together, and an electroscope can show whether something is charged.
Follow the glass-rod-and-cloth picture and see which way the electrons cross.
Where Does Electricity Come From?
If you cannot tell how charge splits when two objects are rubbed, it is easy to read the scene as if only one side became electric and the other stayed as it was. Before rubbing, both sides are neutral; protons stay bound in the nucleus, and the only particles that actually cross are electrons. Electrons that were already there lean to one side, so one object looks (+) and the other (−), and the total charge is the same before and after the rub. Like signs push and unlike signs pull, so you have to decide what moved before the direction of the force can be read correctly.
🧤 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
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Electron transfer between a glass rod and cloth via friction
The left box is a glass rod and the right box is a cloth; plus marks stay inside the rod, and minus marks for electrons are split between the two boxes. Changing the number of transferred electrons from 0 through 5 changes how many minuses remain on the rod and how many have gone to the cloth; when the transferred count is 1 or more, dashed arrows run from the rod toward the cloth and the labels (+) positive and (−) negative appear underneath. At 0 both sides are marked neutral. The other picture has two circles; choosing (+) and (+), (−) and (−), or (+) and (−) places the circles farther apart with outward arrows when the signs match, and closer together with inward arrows when the signs differ.
3
💡 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 → (−)
It is easy to draw positive charge flowing when you rub, but the particle that changes place is the electron; protons stay in the nucleus. A glass rod that looks (+) has lost electrons toward the cloth, and the cloth looks (−). The metal leaves of an electroscope spread because like signs push each other, so drawing particles as if they traveled in the (+) direction just because of the sign reverses the story. The rule that like signs push and unlike signs pull applies to the signs created by that electron shift.
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Direction of force between like and unlike charges
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
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?
1
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.
2
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?
1
Between charges of the same kind, a repulsive force (pushing apart) acts.
2
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
1
What moves when rubbed is electrons; protons are fixed in the nucleus and do not move.
2
What moves is electrons (①), like charges repel (③), gaining electrons gives a negative charge (④), and unlike charges attract (⑤).