Stone-faced embankment slopes and joystick: what they have in common

1. Step 1. Stone-faced embankment slopes — is part of — Levee. Slopes reinforced with stone or turf.
2. Step 2. Levee — uses — Universal gravitation. The weight of the embankment holds back the water.
3. Step 3. Universal gravitation — is used in — Pin tumbler lock. The pins drop into holes in the bolt under their own weight.
4. Step 4. Pin tumbler lock — is part of — Lock and key. The pins keep the cylinder from turning without a key.
5. Step 5. Lock and key — has part — Spring. Springs press the pins.
6. Step 6. Spring — is part of — Joystick. They return the stick to the centre.

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