Bobsleigh and pneumatic tube: what they have in common

1. Step 1. Bobsleigh — has part — Steering wheel. A steering wheel.
2. Step 2. Steering wheel — has part — Airbag. An airbag hides in the steering wheel and inflates instantly in a crash.
3. Step 3. Airbag — uses — Chemical reaction. The gas comes from an instant reaction of sodium azide.
4. Step 4. Chemical reaction — is used in — Capsule. The shell dissolves in the stomach.
5. Step 5. Capsule — is part of — Pneumatic tube. A container for letters.

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