Balloon envelope and barrel: what they have in common

1. Step 1. Balloon envelope — is part of — Hot air balloon. A nylon canopy that holds the heated air.
2. Step 2. Hot air balloon — uses — Convection. Hot air rises and fills the canopy.
3. Step 3. Convection — is used in — Hypocaust. Hot air under the floor.
4. Step 4. Hypocaust — is made of — Brick. The pillars of a hypocaust are brick.
5. Step 5. Brick — is material for — Arch. Arches were built of brick or stone.
6. Step 6. Arch — works like — Barrel. Staves squeezed by hoops hold their shape by the same compression as the stones of an arch.

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