Power in the Past
In the past the use of water as a power source was different to how it is used today. The movement in flowing water was used to turn water mills and other machinery, using the kinetic energy rather than converting it to electrical energy first. Later on steam or water vapour was used so flowing water was not required, but a heat source was.
Water under the bridge
Water has been used as a power source since the times of the Roman Empire, in 510BC, when water mills were used. The water was used to produce flour from grain, rather than to create electricity from the movement of water. The water mill used a water wheel which was turned by a river or stream. This then would drive the mechanism used to crush the grain into flour. Other uses of hydropower were for irrigation, textile manufacturing and in sawmills.
The industrial revolution was an important period in our history. Water played an important role in this change, partially the use of canals as transport but more importantly the use of steam power. The water was heated, often by a coal fire, and the steam would be used to do mechanical work. This made it possible for steam powered ships, locomotives, road vehicles and more to be used as transport.
The water is heated by a boiler and then expands, causing increased pressure, because the atoms have more energy so move more. This increased pressure would be used to push a piston then as the water cooled and contracted the piston would return to its original position
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Google Definition Irrigation
Google Definition Hydropower
Google Definition Kinetic Energy
Wikipedia Article Industrial Revolution
Wikipedia Article Steam Power