Neodymium magnet e railway semaphore: o que têm em comum

1. Passo 1. Neodymium magnet — é um tipo de — Permanent magnet. A kind of magnet.
2. Passo 2. Permanent magnet — funciona como — Eletroímã. An electromagnet attracts iron like a permanent magnet, but only while current flows.
3. Passo 3. Eletroímã — faz parte de — Relay. An electromagnet switches the contacts.
4. Passo 4. Relay — faz parte de — Traffic light. Relay controllers.
5. Passo 5. Traffic light — evoluiu de — Railway semaphore. The first traffic light was a railway-style semaphore.

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