Tennis racket and elevator: what they have in common

1. Step 1. Tennis racket — is made of — Sinew. The strings are natural gut.
2. Step 2. Sinew — is material for — Catapult. Torsion springs were twisted from sinew.
3. Step 3. Catapult — evolved into — Trebuchet. The trebuchet replaced torsion engines as a more powerful siege machine.
4. Step 4. Trebuchet — uses — Counterweight. A falling counterweight swings the throwing arm.
5. Step 5. Counterweight — is used in — Elevator. A counterweight balances the car.

Open Evothings