Pat Anderson":9sqx2khs said:
Guys - the opposite of negative pressure at the outlet is positive pressure at the inlet!
Actually, from physics point of view, there is no such thing as suction!
But don't tell that to the wrong persons under the wrong circumstances!
There is only positive pressure. A difference is positive pressure from one place to another place results in fluid (air or liquid) flow from one place to the other.
Therefore, you really can't suck on anything, but you can create a region of lower pressure, which then allows the greater force behind the higher pressure region to push that liquid in the direction of the lower pressure.
This is important in all types of science, from the weather to space travel to hydraulics to automotive engineering.
If you get a glass tube 100 feet long, put one end under water, and put a vacuum pump at the top end and run it for a long period, you'll find that you can't "suck" the water up any higher than about 33 feet or so. That's because even with zero pressure at the top end, the air pressure pushing down on the water's surface can't push the water up into the tube any more than the 33 or so feet, depending on the air pressure that day.
Incidentally, we've created a barometer in the process above, and can now use it to measure the air pressure and variations as the hours and days go by.
The inconvenience of the 30+ foot tube leads instrument makers to use liquid mercury instead of water, as the density of mercury is 13.5 g/cm∧3 , or 13.5 times that of water, and the liquid column can be shorted proportionately (inversely), to about 30 inches. (Most modern mobile barometers are aneroid, using a bellows tank that expands and contracts to measure air pressure.)
This also means that the same weight of force or pressure equaled by the 33 feet of water column works under water, too. So for every 33 feet you go down under water, the pressure created by the weight of the liquid above goes up by the equivalent of one atmosphere, or about 15 lbs, per square inch, so that at 66 feet, there's 2 atmospheres, or about 30 lbs/sq.", and at 330 feet, 10 atmospheres, or about 150 lbs./sq. ".
Bla, bla, bla, etc.
Now how much of that did you suck up and was it worth it? :lol:
Joe. :teeth :thup