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Mountain rivers flow at superhigh speeds because they are steep. The rivers strip away bits of rock and carry them downhill.
After thousands of years, the river strips away enough rock to form a canyon. That’s a wide, deep crack in solid rock. If water can carve a huge canyon, imagine what else it can do. People put water to work long ago. They used it to move heavy objects, to travel down rivers and across oceans, and even to keep time. Here are just a few of the water-powered machines and systems humans have built.
◀ Water clocks have been around for thousands of years. This fifth-century B.C. clepsydra (water clock) may have been based on Egyptian clocks of the fourteenth century B.C. If so, it was probably used as a way of telling the time during the night. Every evening, it was filled with water. The water flowed gradually through a hole near the base. The passage of time was measured by how far the water had dropped below the “hour” marks that could be seen inside.
▲ Hydrofoils are boats with underwater wings, or foils, which act like airplane wings. The water passing above the foils moves faster than the water traveling below them. The faster water lowers the pressure above the foils. So, the slower water pushes up, creating a force called lift. This force literally lifts the hydrofoil above the water!
▲ Water mills work like windmills, except they are powered by moving water—not wind. The ancient Romans used water mills 2,000 years ago. Water flowed downhill, forcing a series of paddle wheels to turn. The wheels then rotated gears that powered machines. The machines ground corn, among other jobs.
◀ Pyramid builders of ancient Egypt used water in their work. They poured buckets of water onto a mud-and-rubble ramp, making it slippery. Behind them, workers dragged two-ton blocks of stone strapped to wooden platforms. The slippery ramp let the platforms slide more easily to the top.
Fuel cells combine hydrogen and oxygen to create water and electricity. In space, they provide astronauts with drinking water and energy. On Earth, some cars and buses use fuel cells for power. The driver “fills up” the vehicle’s tank with hydrogen gas. The fuel cells take in oxygen from the air. The water is drained off, and the electricity powers the vehicle. ▶
Steam Power
Here’s how steam-powered ships of the nineteenth century used water to travel on water. ▼
The motion of the piston makes other parts of the furnace move. These different components help to turn a giant paddle wheel. The paddle wheel pushes water backward, which pushes the steamship forward.
The pressure forces the piston to move out. As the steam cools and condenses back into water, the piston drops back.
Heat from the furnaces boils water and converts it to steam. The steam heats up even more, and the water vapor expands. It puts pressure against the movable part of the furnace, called the piston.
Below decks, the ships carry huge stores of coal. Sailors constantly shovel the coal into hot furnaces.
