Windscreen wiper and rocket: what they have in common

1. Step 1. Windscreen wiper — is made of — Vulcanized rubber. The blade is rubber.
2. Step 2. Vulcanized rubber — is material for — Weather balloon. The envelope is rubber or latex.
3. Step 3. Weather balloon — is made of — Hydrogen. Filled with hydrogen or helium.
4. Step 4. Hydrogen — is used in — Liquid-propellant rocket engine. Hydrogen is an efficient fuel.
5. Step 5. Liquid-propellant rocket engine — evolved from — Rocket. Goddard switched to liquid fuel.

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