Electromagnetic waves and sickle: what they have in common

1. Step 1. Electromagnetic waves — is used in — Radar. Radio waves reflect off the target.
2. Step 2. Radar — works like — Sonar. The same echolocation principle: sound in water instead of radio waves.
3. Step 3. Sonar — is part of — Submarine. Underwater acoustics.
4. Step 4. Submarine — has part — Diesel engine. Diesel-electric submarines.
5. Step 5. Diesel engine — is part of — Combine harvester. Self-propelled combines run on diesels.
6. Step 6. Combine harvester — evolved from — Sickle. The machine replaced reaping by hand.

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