Hot air balloon and steam turbine: what they have in common

1. Step 1. Hot air balloon — evolved into — Airship. A steerable balloon.
2. Step 2. Airship — uses — Hydrogen. Zeppelins were filled with hydrogen.
3. Step 3. Hydrogen — is used in — Liquid-propellant rocket engine. Hydrogen is an efficient fuel.
4. Step 4. Liquid-propellant rocket engine — has part — De Laval nozzle. A nozzle.
5. Step 5. De Laval nozzle — evolved from — Steam turbine. De Laval invented the nozzle for a steam turbine.

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