Steel edges and voltaic pile: what they have in common

1. Step 1. Steel edges — is part of — Snowboard. They cut the snow in a turn.
2. Step 2. Snowboard — evolved from — Surfboard. Surfing on snow.
3. Step 3. Surfboard — uses — Archimedes’ principle. Buoyancy.
4. Step 4. Archimedes’ principle — is used in — Hydrometer. A hydrometer floats: the buoyant force depends on the liquid's density, so how deep it sinks shows the density.
5. Step 5. Hydrometer — is used in — Lead–acid battery. A car battery's charge is checked with a hydrometer by the density of its acid.
6. Step 6. Lead–acid battery — evolved from — Voltaic pile. Planté’s battery developed the idea of a chemical current source by making it rechargeable.

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