Cutting edge ring and heron’s aeolipile: what they have in common

1. Step 1. Cutting edge ring — is part of — Tunnelling shield. The cutting edge of the shield.
2. Step 2. Tunnelling shield — works like — Dynamite. Two ways of driving tunnels — mechanical and explosive.
3. Step 3. Dynamite — evolved from — Gunpowder. A replacement for gunpowder in mining.
4. Step 4. Gunpowder — is used in — Rocket. The first rockets were powered by gunpowder.
5. Step 5. Rocket — uses — Reaction force. A rocket moves by reaction force.
6. Step 6. Reaction force — is used in — Heron’s aeolipile. Jets of steam spin the ball by reaction force.

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