How the three ways of charging compare
| Friction | Contact | Induction |
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| What gets charged | Two different insulators, rubbed against each other (an amber rod and fur) | An uncharged conductor (a metal sphere) | An uncharged conductor (a metal sphere) |
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| Do they touch? | Yes: they are rubbed together | Yes: the charged conductor touches it | No: the charged object is only brought close |
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| Which electrons move, and where | Electrons go from one insulator to the other | Free electrons go between the charged conductor and the uncharged one | Free electrons flow between the conductor and the Earth, through the earth wire |
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| Earth wire needed? | No | No | Yes: connected, then removed while the charged object is still near |
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| Charge gained | The two insulators gain equal and opposite charges | The same sign as the charged conductor | The opposite sign to the charged object |
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- In all three, only electrons move from one object to another. The number of protons does not change.
- Charge is not created or destroyed: an object becomes negative by gaining electrons, and positive by losing them.