Catapult and telephone: what they have in common

1. Step 1. Catapult — is made of — Sinew. Torsion springs were twisted from sinew.
2. Step 2. Sinew — is material for — Tennis racket. The strings are natural gut.
3. Step 3. Tennis racket — is made of — Carbon fibre. Modern frames.
4. Step 4. Carbon fibre — is made of — Carbon. Carbon.
5. Step 5. Carbon — is material for — Hearing aid. The first hearing aids used a carbon microphone.
6. Step 6. Hearing aid — evolved from — Telephone. The first electric hearing aids were built from telephone components.

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