MadSci Network: Physics Query:

### Re: Can the wind suck the air out of your lungs?

Date: Thu Nov 16 08:11:40 2000
Posted By: Kenneth Chivers, Grad student, B.S. Aerospace Engineering, In school for MBA:Management of Information Systems, NAWCAD, Lakehurst, NJ
Area of science: Physics
ID: 974131442.Ph
Message:

Yes, the wind can suck the air out of your mouth or make it harder to get your breath. However, it would take a SIGNIFICANT pressure loss infront of your mouth to actually suck the wind out of your lungs. I apologize if this response appears to be overly long. Though this observation may be easy to conceptualize, it's a lot more difficult to explain.I broke this into two parts a brief explanation and a more detailed explanation.

As your observations have shown, your lungs operate by using one fundamental fact in nature. Air (any gas) flows from a region with higher pressure to a region with a lower pressure. This is one significant reason why storm fronts form along pressure gradients in the atmosphere. The Bernoulli effect is a prime driver/governing model of how any given mass of air will react to its environment, I explain how this could affect the pressure later.

In order to breath, your lungs must expand and contract, an involuntary muscular reaction controlled by the muscles in your diaphram. As your lungs expand, they create a lower pressure region by increasing their volume. When your lungs contract, they decrease their volume and increase their pressure. At lower pressure, high altitude regions, not only is the air more scarce (less oxygen), but the pressure actually fights your lungs' ability to draw in the needed air, forcing them to depend on quicker gulps of air, requiring them to breath harder. ,p> In your situation, you were hiking on the leeward side (away from the prevalent wind) of the mountain. When the wind is forced to rise over a tall ubstruction like a ridge, it slows down and builds up pressure on the windward side. On the leeward side, as it decends down the obstruction the pressure decreases rapidly and the wind accelerates accordingly. When this happens, the pressure around a hiker on the leeward side can be significantly lower than what their lungs may normally be used to.

To you, it would feel as if the wind were being sucked out of your lungs, when in actuality, your lungs may have been unable to draw a proper breath in a particularily strong gust due to the rapid pressure decrease around your mouth. This unexpected pressure decrease would only be compounded by the altitude of your position, forcing your lungs to work extra hard to bring in the needed air, and if your lungs didn't expand quickly enough or wide enough, then they may not have drawn any air in at all. Must have been a great view though :)

Bernoulli's Effect on this observation The Bernoulli effect may also bare some responsability for this situation. Bernoulli models the effects on an air flow, due to the laws of conservation (mass, energy, and momentum). This effect models how the velocity profile (true velocity as well as all of the velocity components that characterize the air flowing around you in this situation) of the air may change as it reacts to its environmental surroundings and environmental characteristics, such as temperature, external pressure changes, and obstructions (you and the mountains, etc...)

Begin by picturing a unit cube of air mass and two points on a line representing the same unit mass at two different times and locations. The environmental characteristics between these two points govern how the unit volume will react by the time it reaches the second point. For instance if the temperature changes in the enviornment, the gas laws dictate a change in volume, where Volume is proportional to Temperature by a gas constant peculiar (unique) to the gases represented in the unit mass. In general, as the temperature increases, the volume increases and as the temperature decreases the volume decreases. The pressure of a gas is similarly related, being proportional to the volume. Bernoulli's effect expands greatly upon this simple truth.

Remember the picture we painted with the two dots, connected by a line, representing a change in time and location, from beginning to end, with all the environmental affects dictating the changes we see in our cube of air by the time it gets to the end of the line. Now, super-impose this image to your hiking trip, the wind blwing across the top of the range, and you hiking on a ridge below the crest of the range on the leeward side as discribed far above in my response.

Put the first dot at the top of the mountain, and the second dot where you are on the lower ridge. The air has been compressed by its fight to get over the mountain, due to the Bernoulli effect's demand for conservation of mass and energy, and momentum. Here the mountain (a serious obstruction) forced the air to climb or convert some of its kinetic energy into potential energy. Due to the Bernoulli effect, as the velocity decreases, mass stays constant, pressure increases, the air becomes compressed and converts the lost kinetic energy(when it was moving faster) to potential energy by compressing its volume and increasing its density and the air temperature decreases. The characteristics, then for the first dot are a compressed volume, cold temperature, and a high potential energy (depending on how fast the air was moving before it climbed the mountain.)

You are the second dot, at a lower altitude, the potential energy is rapidly converted back to kinetic energy via the conservation of the air's original momentum (ignoring any loss to entropy or friction affects-this would make the explanation a little too extensive...) and thus increasing the velocity, reducing the pressure, increasing the volume, and strangely enough increasing the temperature. This is also how a chinook (or warming wind) is formed.

So, if the wind was gusting extremely hard on the other side of the mountain, then it may have been gusting even harder at your location, depending on how far you were from the crest of the range. The pressure drop for a such a significant gust may have been enough to overtake your lungs' ability to bring in air, or if your were breathing out at the time, the wind may even have been sucked out of you!

Thanks for the question.

Ken C.

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