Crutch handgrip and vacuum pump: what they have in common

1. Step 1. Crutch handgrip — is part of — Crutches. A grip for the hand.
2. Step 2. Crutches — evolved into — Wheelchair. Mobility aids.
3. Step 3. Wheelchair — has part — Ball bearing. Bearings.
4. Step 4. Ball bearing — is part of — Induction motor. Bearings.
5. Step 5. Induction motor — has part — Stator. The windings create a rotating field.
6. Step 6. Stator — is part of — Vacuum pump. A cylindrical chamber.

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