The bladed spinning machine that converts the energy of moving fluid into rotary motion — and the device through which almost all the world's electricity passes, whether the fuel is coal, gas, nuclear, water, or wind.
Almost every time you flip a light switch, somewhere a shaft is spinning. Coal, nuclear, geothermal, and concentrated-solar plants make heat that boils water and drives a steam turbine. Natural-gas plants often burn fuel in a combustion turbine directly, and the most efficient add a second steam turbine running on the waste heat. Hydroelectric dams spin water turbines; wind farms spin air turbines. Solar panels are the major exception — they make electricity with no moving part at all. Apart from solar and a few smaller technologies, almost all large-scale generation still runs through spinning machinery. The turbine is the hidden heart of the modern energy system — the machine civilization built to turn heat, water, and wind into the current in the wire.