Military radio and archimedes’ screw: what they have in common

1. Step 1. Military radio — has part — Antenna. It needs an antenna.
2. Step 2. Antenna — is part of — Radar. An antenna emits and receives.
3. Step 3. Radar — works like — Sonar. The same echolocation principle: sound in water instead of radio waves.
4. Step 4. Sonar — is part of — Submarine. Underwater acoustics.
5. Step 5. Submarine — has part — Propeller. A propeller.
6. Step 6. Propeller — evolved from — Archimedes’ screw. The first propellers by Smith and Ericsson were a variation on the Archimedes’ screw.

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