Rubber crutch tip and aerosol can: what they have in common

1. Step 1. Rubber crutch tip — is part of — Crutches. It prevents slipping.
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 — Revolving door. The axis.
5. Step 5. Revolving door — uses — Pressure. It keeps warm air in.
6. Step 6. Pressure — is used in — Aerosol can. A propellant gas.

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