Turbines

Two of the earliest sources of power for driving machinery were the waterwheel and the windmill . The waterwheel has little paddies or buckets mounted around the edge. When it is placed in a stream , the  flowing water spins it around . A windmill  has large sails, which turn when the wind blows through them.

Waterwheels and windmills are no used for dri-ving machinery today. But we do find uses for modern versions of them -water and wind turbines . Water turbines are the most useful. They are used to harness the energy in flowing water to drive electricity generators in hyroelec- tric power schemes.
Q What does the word "hydroelectric" literally mean?