Kettle spout and boyle’s air pump: what they have in common

1. Step 1. Kettle spout — is part of — Kettle. A drain.
2. Step 2. Kettle — evolved into — Electric kettle. A kettle with a heater.
3. Step 3. Electric kettle — has part — Heating element. A heating element in the base heats the water.
4. Step 4. Heating element — works like — Incandescent light bulb. A lamp and a heater use the same effect — a conductor heated by current; they differ in purpose, light or heat.
5. Step 5. Incandescent light bulb — uses — Vacuum. The bulb was evacuated so the filament would not burn out.
6. Step 6. Vacuum — is used in — Boyle’s air pump. The pump draws out the air.

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