Barrel and smartphone: what they have in common

1. Step 1. Barrel — works like — Arch. Staves squeezed by hoops hold their shape by the same compression as the stones of an arch.
2. Step 2. Arch — is part of — Amphitheatre. Arcades.
3. Step 3. Amphitheatre — works like — Stadium. The Greek stadium is older than the Roman amphitheatre; modern stadiums combine both layouts.
4. Step 4. Stadium — has part — Street light. Floodlights.
5. Step 5. Street light — has part — LED. LEDs.
6. Step 6. LED — is part of — Smartphone. The camera flash.

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