Speedometer and modem: what they have in common

1. Step 1. Speedometer — has part — Permanent magnet. A rotating magnet drags the needle.
2. Step 2. Permanent magnet — is part of — Loudspeaker. A permanent magnet.
3. Step 3. Loudspeaker — is part of — Telephone. The earpiece reproduces the other person’s voice.
4. Step 4. Telephone — is used in — Modem. It works over a telephone line.

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