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Rudi Kiefer: Water pressure an important force in our daily lives
Rudi Kiefer
The laws of hydraulic action affect our everyday lives more than one might be aware. If you drove a car today, and used the brakes, you were using hydraulic action. If you opened a water faucet today, you were using hydrostatic action, which is somewhat similar.

Both the hydraulic and the hydrostatic principles use the fact that fluids aren’t compressible. You can’t squeeze a gallon of water into a pint bottle.

When we open the kitchen faucet, we expect a steady flow of water, without spattering or trickling. This would be difficult to accomplish directly with pumps, because pump pressure can change easily. Hydrostatic methods work much better. Community systems use pumps to keep a water tower reservoir filled. This tank needs to be taller than the highest building it serves. The weight of the water in the tank provides even pressure in the lines. That’s why water tanks are raised high and not underground. Skyscrapers have their own water tanks on their rooftops. If the level in a municipal water tank decreases due to high usage, the line pressure will also drop.

Hydraulic systems work in a similar way, but not with the weight of water. Instead of gravity providing the force, a noncompressible fluid is pressurized by a pump. Water is non-compressible, but we can’t use it in the brake lines of a car. The heat generated by the brakes would make it evaporate. Water vapor is a gas, therefore it’s compressible, and hydraulic action is lost.

One reason brakes can get spongy or even fail over time is the absorption of water in the brake fluid (which is an oil). Like any hydraulic fluid, brake fluid must be changed regularly to remain effective.

The biggest hydrostatic display in our area is Lake Lanier. You can see the Chattahoochee River supplying water into it. But the really big feeder is invisible: the groundwater, contained in the bedrock of the hills around and above the lake.

When rain penetrates the ground nearby, the weight of the water inside the bedrock creates upward pressure underneath the lake bed.

Consequently, the lake level rises. During drought, less groundwater is available, and the lake level drops.

Of course, Lanier is artificial, like all lakes in North Georgia. Lake levels can be modified and controlled by the engineers at the dam.

Rudi Kiefer, Ph.D., is a professor of physical science and director of sustainability at Brenau University. His column appears Sundays and at

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