Dam and joystick: what they have in common

1. Step 1. Dam — is made of — Reinforced concrete. Concrete dams.
2. Step 2. Reinforced concrete — is material for — Skyscraper. Reinforced concrete.
3. Step 3. Skyscraper — has part — Elevator. A skyscraper is impossible without a lift.
4. Step 4. Elevator — has part — Elevator safety brake. Otis’s safety brakes.
5. Step 5. Elevator safety brake — has part — Spring. Springs throw out the catches when the rope goes slack.
6. Step 6. Spring — is part of — Joystick. They return the stick to the centre.

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