When I was a kid I was always challenging myself to swim to the bottom of the pool. (This was when pools were deeper than 5 feet.) The eight foot deep pool at my neighbor’s house was easily conquered, but the twenty footer at the country club was quite a challenge (especially since we weren’t actually members at the club). When I finally got all the way down to tag the bottom (staying clear of the drain thanks to a random episode of Baywatch) I noticed a little pain in my ears. Twenty feet of water was pushing down on me and my ears were feeling the pressure.
The technical term for what I was feeling is hydrostatic pressure. As dictionary.com explains it:
The pressure exerted by a fluid at equilibrium at a given point within the fluid, due to the force of gravity.
In layman’s terms… it’s the weight of a fluid (usually water) pressing down. Hydrostatic pressure is the reason it’s so difficult to recover shipwrecks and why we can’t make it to the deep ocean bottom.
It may sound like scientific jargon, but a practical understanding of hydrostatic pressure can be useful. For instance, an above ground swimming pool would have a drain at its bottom. Take a hose and attach it to the pool drain turned so the water shoots up. Instant fountain. And the height of the water fountain is the same as the depth of the water in the pool thanks to hydrostatic pressure. As the depth in the pool starts to go down the fountain would also get shorter and shorter.
The most important thing though…. hydrostatic pressure is dependent on the depth of the water, not the volume. So the fountain would be just as high whether it was caused by a 30 ft pool, or a 2 ft barrel. This is why rain barrels are useful.
Now that we’ve got this far, I can explain how hydrostatic pressure makes your ears pop when you travel to higher elevations. The principle of hydrostatic pressure applies to air just like it does to water. We live at the bottom of a seven mile deep atmosphere which causes a significant hydrostatic pressure on our bodies. This is called ‘standard pressure’ or ‘one atmosphere, and is equivalent to about 33 ft of water. When you drive up into the mountains you suddenly are experiencing a lower hydrostatic pressure, while your ears still have the higher pressure internally. The popping is part of the mechanism for adjusting the pressure inside your ear to be the same as the outside pressure. For the anatomical explanation, try this.
Hydrostatic pressure makes beer bongs possible, and is key to water filtration in all kinds of ways. Next time I’m going to explain how hydrostatic pressure makes sure water comes out of your faucets on demand.