Spear-thrower shaft and archimedes’ screw: what they have in common

1. Step 1. Spear-thrower shaft — is part of — Spear-thrower. A lever that extends the arm.
2. Step 2. Spear-thrower — has part — Hook spur. A hook against which the dart rests.
3. Step 3. Hook spur — is part of — Corkscrew. A rest on the bottle neck for the lever.
4. Step 4. Corkscrew — uses — Screw. A spiral.
5. Step 5. Screw — is used in — Archimedes’ screw. A rotating helical surface lifts water.

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