# Is this an elaborate whoosh? Is geometry a force? **URL:** \ **Category:** Great Debates\ **Created:** [August 25, 2009, 11:23pm UTC](https://boards.straightdope.com/t/is-this-an-elaborate-whoosh-is-geometry-a-force/507708 "2009-08-25T23:23:22Z")\ **Posts on this page:** 20\ **Page:** 1
**Author:** ![rwjefferson](https://avatars.discourse-cdn.com/v4/letter/r/a6a055/32.png) [@rwjefferson](https://boards.straightdope.com/u/rwjefferson)\ **Post date:** [August 25, 2009, 11:23pm UTC](https://boards.straightdope.com/t/is-this-an-elaborate-whoosh-is-geometry-a-force/507708/1 "2009-08-25T23:23:22Z")
**movingfinger:** You are the first to show even attempt understanding. Honest questions deserve honest answers. you say inverse; I say in verse you say an elaborate whoosh; I say continued propagation by dogma. [The Smithsonian National Air and Space Museum](http://www.nasm.si.edu/exhibitions/gal109/NEWHTF/HTF511.HTM) is charged with teaching teachers and students and lovers of lift and flight. In so many words and exhibits, the message laid out clear. The shape and tilt of wing causes air to flow faster over. Air flowing faster over causes the low pressure that forces lift. shape and tilt of wing is the primary force of wing lift. Is this an elaborate whoosh? First question. Is shape and tilt the primary force of wing lift, really? Peace rwjefferson ---
**Author:** ![cerberus](https://avatars.discourse-cdn.com/v4/letter/c/71e660/32.png) [@cerberus](https://boards.straightdope.com/u/cerberus)\ **Post date:** [August 25, 2009, 11:32pm UTC](https://boards.straightdope.com/t/is-this-an-elaborate-whoosh-is-geometry-a-force/507708/2 "2009-08-25T23:32:25Z")
I believe that this is called the Bernoulli effect. The fluid moves faster over the curved upper surface, with lesser density. The higher density of the fluid flowing under the wing pushes up on the wing, … ---
**Author:** ![kaylasdad99](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/kaylasdad99/32/3398_2.png) [@kaylasdad99](https://boards.straightdope.com/u/kaylasdad99)\ **Post date:** [August 25, 2009, 11:32pm UTC](https://boards.straightdope.com/t/is-this-an-elaborate-whoosh-is-geometry-a-force/507708/3 "2009-08-25T23:32:44Z")
No. Pressure differential between the underside of the wing and the top side of the wing is the primary force of wing lift. Shape and tilt are not, strictly speaking, forces at all. They are factors that influence the way in which the pressure differential is generated, and the amount of pressure differential that is generated. At least, that’s how I interpret the statement in the link. ---
**Author:** ![Mangetout](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/mangetout/32/19_2.png) [@Mangetout](https://boards.straightdope.com/u/Mangetout)\ **Post date:** [August 26, 2009, 12:10am UTC](https://boards.straightdope.com/t/is-this-an-elaborate-whoosh-is-geometry-a-force/507708/4 "2009-08-26T00:10:59Z")
It looks like a simple case of bad wording, rather than bad science (although obviously, it’s both). I think they meant ‘cause’, not ‘force’ - it might even be a transcription error, if someone dictated the text. ---
**Author:** ![Bryan\_Ekers](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/bryan_ekers/32/183_2.png) [@Bryan\_Ekers](https://boards.straightdope.com/u/Bryan_Ekers)\ **Post date:** [August 26, 2009, 12:43am UTC](https://boards.straightdope.com/t/is-this-an-elaborate-whoosh-is-geometry-a-force/507708/5 "2009-08-26T00:43:57Z")
As an incidental note, describing the Bernoulli Effect as a “whooosh” appeals to me as nerd-jokes often do. ---
**Author:** ![Johnny\_L.A](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/johnny_l.a/32/1084_2.png) [@Johnny\_L.A](https://boards.straightdope.com/u/Johnny_L.A)\ **Post date:** [August 26, 2009, 12:46am UTC](https://boards.straightdope.com/t/is-this-an-elaborate-whoosh-is-geometry-a-force/507708/6 "2009-08-26T00:46:58Z")
> [@Bryan\_Ekers](#): > > As an incidental note, describing the Bernoulli Effect as a “whooosh” appeals to me as nerd-jokes often do. I liked it too. ---
**Author:** ![pulykamell](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/pulykamell/32/3166_2.png) [@pulykamell](https://boards.straightdope.com/u/pulykamell)\ **Post date:** [August 26, 2009, 12:55am UTC](https://boards.straightdope.com/t/is-this-an-elaborate-whoosh-is-geometry-a-force/507708/7 "2009-08-26T00:55:40Z")
I’m not sure I like their wording, but here’s [an in-depth](http://warp.povusers.org/grrr/airfoilmyth.html) explanation of what causes lift, and it’s because of a variety of factors, Bournelli’s principle being only partly a contributor, and generally not a contributor in the way most people have been taught (at least when I was in school.) ---
**Author:** ![rwjefferson](https://avatars.discourse-cdn.com/v4/letter/r/a6a055/32.png) [@rwjefferson](https://boards.straightdope.com/u/rwjefferson)\ **Post date:** [August 26, 2009, 12:58am UTC](https://boards.straightdope.com/t/is-this-an-elaborate-whoosh-is-geometry-a-force/507708/8 "2009-08-26T00:58:52Z")
> [@cerberus](#): > > I believe that this is called the Bernoulli effect. The fluid moves faster over the curved upper surface, with lesser density. The higher density of the fluid flowing under the wing pushes up on the wing, … you say fluid; I say [fluent.](http://en.wikipedia.org/wiki/Fluent_%28mathematics%29) Yes. Fluid flowing faster over a surface causes lower pressure. How does curve cause air to flow faster? What is the difference between density and pressure differential? peace rwj ---
**Author:** ![rwjefferson](https://avatars.discourse-cdn.com/v4/letter/r/a6a055/32.png) [@rwjefferson](https://boards.straightdope.com/u/rwjefferson)\ **Post date:** [August 26, 2009, 2:07am UTC](https://boards.straightdope.com/t/is-this-an-elaborate-whoosh-is-geometry-a-force/507708/9 "2009-08-26T02:07:57Z")
> [@kaylasdad99](#): > > Pressure differential between the underside of the wing and the top side of the wing is the primary force of wing lift. Can you name the force that causes pressure differential? rwj ---
**Author:** ![Chronos](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/chronos/32/134_2.png) [@Chronos](https://boards.straightdope.com/u/Chronos)\ **Post date:** [August 26, 2009, 2:21am UTC](https://boards.straightdope.com/t/is-this-an-elaborate-whoosh-is-geometry-a-force/507708/10 "2009-08-26T02:21:48Z")
If the so-called Bernoulli effect were the real cause for lift, then it would be possible to create a symmetric wing which would produce lift when moved forward or backwards. This doesn’t actually work, so that’s not the correct explanation for lift. The correct explanation is that a wing is tilted, and as a result deflects air downward, and the air deflected downward exerts an upward force on the wing. A tilted barn door, with no curve whatsoever, will provide lift. I say “so-called Bernoulli effect”, because while there is a real effect called the Bernoulli effect, the whole bit about air flowing faster over the top of the wing isn’t it. ---
**Author:** ![Larry\_Borgia](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/larry_borgia/32/156_2.png) [@Larry\_Borgia](https://boards.straightdope.com/u/Larry_Borgia)\ **Post date:** [August 26, 2009, 2:35am UTC](https://boards.straightdope.com/t/is-this-an-elaborate-whoosh-is-geometry-a-force/507708/11 "2009-08-26T02:35:06Z")
> [@Chronos](#): > > If the so-called Bernoulli effect were the real cause for lift, then it would be possible to create a symmetric wing which would produce lift when moved forward or backwards. This doesn’t actually work, so that’s not the correct explanation for lift. The correct explanation is that a wing is tilted, and as a result deflects air downward, and the air deflected downward exerts an upward force on the wing. A tilted barn door, with no curve whatsoever, will provide lift. > > I say “so-called Bernoulli effect”, because while there is a real effect called the Bernoulli effect, the whole bit about air flowing faster over the top of the wing isn’t it. This is my understanding. But then why are airplane wings given that distinctive shape? ---
**Author:** ![DSYoungEsq](https://avatars.discourse-cdn.com/v4/letter/d/c6cbf5/32.png) [@DSYoungEsq](https://boards.straightdope.com/u/DSYoungEsq)\ **Post date:** [August 26, 2009, 2:49am UTC](https://boards.straightdope.com/t/is-this-an-elaborate-whoosh-is-geometry-a-force/507708/12 "2009-08-26T02:49:37Z")
Um, y’all, don’t you recall [the last time that **rwjefferson** got the ball rolling on this issue](http://boards.straightdope.com/sdmb/showthread.php?p=6371426&#post6371426)? True, he wasn’t the OP last time, but his was the significant contribution to wrangling that spanned three years. 😉 ---
**Author:** ![rwjefferson](https://avatars.discourse-cdn.com/v4/letter/r/a6a055/32.png) [@rwjefferson](https://boards.straightdope.com/u/rwjefferson)\ **Post date:** [August 26, 2009, 2:59am UTC](https://boards.straightdope.com/t/is-this-an-elaborate-whoosh-is-geometry-a-force/507708/13 "2009-08-26T02:59:40Z")
> [@Chronos](#): > > …the whole bit about air flowing faster over the top of the wing isn’t it. Air flowing faster over the top of a wing is an effect of lift. effect is not the same as cause Pressure differential is the primary force that levitates a wing. Lower pressure differential results in verse greater fluid velocity over a wing. bernoulli Can you name the force that causes in verse pressure differential? rwj ---
**Author:** ![rwjefferson](https://avatars.discourse-cdn.com/v4/letter/r/a6a055/32.png) [@rwjefferson](https://boards.straightdope.com/u/rwjefferson)\ **Post date:** [August 26, 2009, 3:03am UTC](https://boards.straightdope.com/t/is-this-an-elaborate-whoosh-is-geometry-a-force/507708/14 "2009-08-26T03:03:30Z")
> [@Larry\_Borgia](#): > > This is my understanding. But then why are airplane wings given that distinctive shape? To guide the force that causes in verse pressure differential more efficiently downward. rwj ---
**Author:** ![kaylasdad99](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/kaylasdad99/32/3398_2.png) [@kaylasdad99](https://boards.straightdope.com/u/kaylasdad99)\ **Post date:** [August 26, 2009, 5:40am UTC](https://boards.straightdope.com/t/is-this-an-elaborate-whoosh-is-geometry-a-force/507708/15 "2009-08-26T05:40:24Z")
> [@rwjefferson](#): > > Can you name the force that causes pressure differential? > > rwj No. I don’t have the aerodynamics chops for it. But I’m also not buying outright the notion that the pressure differential is caused by a force. ---
**Author:** ![Beware\_of\_Doug](https://avatars.discourse-cdn.com/v4/letter/b/278dde/32.png) [@Beware\_of\_Doug](https://boards.straightdope.com/u/Beware_of_Doug)\ **Post date:** [August 26, 2009, 7:17am UTC](https://boards.straightdope.com/t/is-this-an-elaborate-whoosh-is-geometry-a-force/507708/16 "2009-08-26T07:17:46Z")
**Is geometry a _farce_?** No. You can tell because geometric theorems rarely involve door-slamming or illicit sex. ---
**Author:** ![Whack-a-Mole](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/whack-a-mole/32/141_2.png) [@Whack-a-Mole](https://boards.straightdope.com/u/Whack-a-Mole)\ **Post date:** [August 26, 2009, 7:45am UTC](https://boards.straightdope.com/t/is-this-an-elaborate-whoosh-is-geometry-a-force/507708/17 "2009-08-26T07:45:06Z")
> [@Larry\_Borgia](#): > > This is my understanding. But then why are airplane wings given that distinctive shape? The Master speaks (and as noted above this has been done here): > [@](#): > > Of all the flawed explanations of why planes fly, the one most people have heard involves the Bernoulli principle and “equal transit times.” The curved upper surface of the wing is longer than the bottom one, we’re told, and the air above the wing must therefore speed up to keep pace with its counterpart below. Start with this increased velocity on the top of the wing, mix in Bernoulli’s principle, and you find lower pressure above. This pressure differential sucks the airplane upward and voilà! A quarter-million pounds of jumbo jet stays aloft. > > This logic is taught to students of all ages, and finds its way into many respectable science textbooks. Its only problem is its complete lack of resemblance to reality. A given “piece” of upper-surface air has no compelling reason to keep pace with its estranged sibling below; it can’t know and doesn’t care what’s happening on the other side of that aluminum partition. > > That’s not to say this model totally misses the mark; it just underestimates the effect. The air really does accelerate over the top of the wing, but actually far outpaces the lower-surface air. It’s a good thing, too–if the air stayed in sync over the minuscule difference between the upper and lower paths, a Cessna 152 would have to fly at over 300 mph just to stay in the air! (In reality, it’s about 55 mph.) > > By this point I’m sure you’re tired of hearing all the non-reasons airplanes fly and would like a real answer. Where does lift come from? One important fact is that fluids have a tendency to adhere to curved surfaces as they flow past. This is called the Coanda effect. The explanation for it is outside the scope of this article, so you’ll have to take my word for it or check out the references. The bottom line is that if you correctly shape the top of the wing, the air will keep hugging the surface as it passes. > > The next step is realizing that when a fluid is made to curve, its pressure is “thrown” to the outside by centrifugal force (that’s the simplest way of describing it). As the air crests the hill at the top of the airfoil, it pulls away from the wing surface, creating a slight vacuum next to the metal. The pressure differential helps push the wing up. In addition, the wing causes the flow behind it to move downward. Some of the downward flow is caused by air deflected by the lower surface, and some comes from air that is forced down as it rounds the top. (That’s where the missing lift we mentioned in connection with the AOA explanation comes from!) In short, an airfoil generates lift up by deflecting the air flow down, a clear example of Newton’s Third Law. This illustration makes the notion of downward deflection a little clearer. > > Is it wrong to invoke the Bernoulli principle when explaining how an airfoil works? No, but it tends to confuse matters for the non-technical audience. In fact, airfoils can be explained in two ways. I’ve just given the “Newton” explanation–a wing generates lift because it deflects the airflow. The “Bernoulli” explanation has to do with pressure differentials. For complex reasons we needn’t get into (other than to say they have little to do with equal transit times), air moves faster over the top of a wing than beneath it. Bernoulli’s principle tells us that the higher the velocity of an airstream, the lower its static pressure. Because the static pressure below the wing is higher than that above, the wing generates lift. If you don’t quite follow all that, don’t worry–the Newton explanation is perfectly adequate. > > SOURCE: [How do airplanes fly, really? - The Straight Dope](http://www.straightdope.com/columns/read/2214/how-do-airplanes-fly-really) For debate on this see the link in **DSYoungEsq’s** post above. That’ll keep you busy awhile. ---
**Author:** ![Half\_Man\_Half\_Wit](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/half_man_half_wit/32/21766_2.png) [@Half\_Man\_Half\_Wit](https://boards.straightdope.com/u/Half_Man_Half_Wit)\ **Post date:** [August 26, 2009, 8:34am UTC](https://boards.straightdope.com/t/is-this-an-elaborate-whoosh-is-geometry-a-force/507708/18 "2009-08-26T08:34:38Z")
I remember reading that one of the reasons (if not _the_ reason) airfoils have the shape they do is because those shapes can be obtained in a mathematically simple way by performing a [Joukowski transform](http://en.wikipedia.org/wiki/Joukowsky_transform), which takes a circle in the complex plane to something that looks very much like that classic wing shape; so you can just compute the airflow around a circular ‘wing’, apply the transform, and you’re done. ---
**Author:** ![njtt](https://avatars.discourse-cdn.com/v4/letter/n/ecd19e/32.png) [@njtt](https://boards.straightdope.com/u/njtt)\ **Post date:** [August 26, 2009, 9:25am UTC](https://boards.straightdope.com/t/is-this-an-elaborate-whoosh-is-geometry-a-force/507708/19 "2009-08-26T09:25:33Z")
The [page linked to](http://www.nasm.si.edu/exhibitions/gal109/NEWHTF/HTF511.HTM) by the OP does not say what he/she says it does. It does not contain the word “force,” or even “cause.” Here is the entire text from the page (apart from links and stuff): > [@](#): > > A wing is shaped and tilted so the air moving over it moves faster than the air moving under it. As air speeds up, its pressure goes down. So the faster-moving air above exerts less pressure on the wing than the slower-moving air below. The result is an upward push on the wing–lift! > > Many factors affect the amount of lift a wing creates: the size and shape of the wing, the angle at which it meets the oncoming air, the speed at which it moves through the air, even the density of the air. Whether or not this is strictly correct, I see nothing there that suggests that geometry is a force. (Surely the OP does not think that the shapes of things have no effect on the ways that they move.) Is the OP an elaborate whoosh? ---
**Author:** ![Cheesesteak](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/cheesesteak/32/3694_2.png) [@Cheesesteak](https://boards.straightdope.com/u/Cheesesteak)\ **Post date:** [August 26, 2009, 10:38am UTC](https://boards.straightdope.com/t/is-this-an-elaborate-whoosh-is-geometry-a-force/507708/20 "2009-08-26T10:38:41Z")
> [@rwjefferson](#): > > Can you name the force that causes pressure differential? The wing could be pushed by an engine, such as with a plane (I’m guessing this is the bush you’ve been beating around) The wing could be falling, such as with a glider The wing could be rotated, as a propeller The wing could be just sitting there during a wind storm. There could be a thousand different ways for the pressure differential to occur. All that is required is a wing that is shaped and tilted correctly while air flows past it. What is important about wing design is the geometry, because it isn’t a wing if the geometry is wrong. [Next page](https://boards.straightdope.com/t/is-this-an-elaborate-whoosh-is-geometry-a-force/507708.md?page=2)