Trackball and hammer: what they have in common

1. Step 1. Trackball — has part — Ball bearing. The ball rotates on supports.
2. Step 2. Ball bearing — is part of — Crankshaft. The main journals of the shaft are bearings (in combustion engines usually plain bearings).
3. Step 3. Crankshaft — is part of — Diesel engine. A crankshaft.
4. Step 4. Diesel engine — has part — Cylinder. Cylinders.
5. Step 5. Cylinder — is part of — Steam hammer. A steam cylinder.
6. Step 6. Steam hammer — evolved from — Hammer. A steam hammer is a hammer lifted by steam, used to forge huge parts.

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