Would it be more difficult do draw water through a straw at sea leavel or on top of a very high mountain?

Answer 1

The higher you go, the more difficult it will be to draw water through the straw, provided the straw is the same length.

In science and engineering, there is no such thing as "suction" - only a differential in pressure. So when you "suck" on the straw, what is happening is you are removing air from the straw and the air pressure in the straw is less than the ambient air pressure. Therefore the ambient air pressure outside the straw will push the water up the straw until the weight of the water column inside the straw is equal to the air pressure differential.

This principal applies to pumps as well. A "suction" pump at sea level is capable of drawing water from about 20 feet down. At 12,000 feet, the same pump can only draw water from about 7.5 feet, both scenarios at 60F. The colder, the more lift is possible. Of course the exact number is influenced by how close to a perfect vacuum the pump can draw air, the barometric pressure, altitude and temperature.

If that still doesn't make sense, let's bring this scenario to an extreme, or the "nth degree." If you have a glass of water in a vacuum, and ignoring the fact that the water will boil due to the zero pressure, there will be no air pressure differential between the straw and the ambient surroundings. Therefore it will not be possible to suck any water out of the straw in a vacuum.

Or let's increase the length of the straw, let's say to 20 feet. At sea level, it will just barely be possible to draw water, but at 12,000 feet the water column will rise to only 7.5 feet.


EDIT:

A note to prettygirl - sorry, I don't sell vacuum cleaners! A vacuum cleaner does not "suck" - what we commonly call "suction" is really the differential in pressure - or the difference in air pressure between the atmosphere and the intake side of the vacuum cleaner. The vacuum cleaner is essentially an air pump which blows air out the "back end", and the "nozzle end" allows air from the atmosphere to replace it. That movement of air moves dirt off the floor with it. So if you put your hand on the end of the nozzle, what seems like sucking is actually air from the atmosphere trying to push your hand into the nozzle because the atmospheric or ambient pressure is greater than the pressure inside the nozzle. I assure you there is no invisible force picking the dirt off your floor, it is only the air rushing in to fill the low pressure area produced by the pump. While the general term for that is suction, you won't find that term used by engineers and scientists. If you still don't believe me, think about trying to use a vacuum cleaner in space where there is no atmoshere. No such thing as suction!

Answer 2

There is no difference in the work (or pressure) required to draw water up a straw. Water moves up the straw whe the pressure on the water surface inside the straw is less than that inside the glass. Regardless of the absolute pressure, if you apply a pressure difference, the water will rise to the same height. The relation between the height (h), pressure difference (p), water density (d) and local gravity is: p = dgh. On a mountian top, gravity is reduced by a miniscule amount (at the top of Mount Everest, gravity is 99.8% of what it is at sea level) and that does reduce the required pressure by an insignificant amount.

The main difference in the two straws lies in how high you can draw the water. You cannot reduce the pressure in the straw below zero. Since the atmospheric pressure at sea level can be twice that on a high mountain, you have more of a pressure difference to work with. At sea level you could draw water to a height of nearly 34 feet. On a high mountain you would be limited to 17 feet.

In both cases, the water at the top of the straw would start to boil although it would not be hot, but that's a subject for another time.

The real difference

Answer 3

More difficult on the top of the mountain.

Understand that the mechanics of drawing a liquid through a straw is not "sucking" it through, as is commonly said. What you suck is the air between your mouth and the liquid within the straw. But atmospheric pressure "pushes" the water up the straw to equalize that pressure difference. Since the atmospheric pressure up high is lower, you have to remove more air pressure inside the straw for there to be a big enough difference in the atmospheric pressure for it to be able to do the "work" of pushing the required volume (weight) of liquid up the straw to your mouth.

Answer 4

Probably very little difference. The air pressure is greater at sea level, which means the pressure at the surface of the liquid is greater at sea level than at altitude. Newton's laws say for ever force there is an equal and opposite reaction force, which means the liquid itself has an upward force to conteract the downward force of air pressure.

When you suck through a straw, you're making a vacuum. The walls of your diaphram are expanding, drawing the liquid in (which you then stop in your mouth before it goes down the wrong way and you die). Since the vacuum that is created is independent of outside air pressure and can be assumed to be constant, and since the resultant upward force is greater at sea level, I would assume the effort required to create the vacuum is less at sea level than on a mountain. And while gravity is less on the mountain, the effect of air pressure on the liquid's surface is orders-of-magnitude more influential. Gravity can be assumed constant.

So to me it would be easier at sea level, but I might be missing something.

Answer 5

Well, it would be more difficult to draw water through a straw on top of the mountain, due to the less atmospheric pressure.

Answer 6

Very high mountain, less atmospheric pressure.

Answer 7

No such thing as suction in engineering? LOL!

You must "suck" as an engineer. Remind me never to buy a vacuum cleaner from you!!