Hydrometer and screw press: what they have in common

1. Step 1. Hydrometer — is used in — Lead–acid battery. A car battery's charge is checked with a hydrometer by the density of its acid.
2. Step 2. Lead–acid battery — is part of — Submarine. Underwater, electric motors run on batteries.
3. Step 3. Submarine — has part — Propeller. A propeller.
4. Step 4. Propeller — uses — Screw. A propeller “screws” itself into the water, like an Archimedes’ screw.
5. Step 5. Screw — is used in — Screw press. The force is produced by turning a screw.

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