Common Misconceptions Many Reasonably Intelligent People Have and Your Corrections

[Shagnasty]

A common misperception is that airplanes can fly because their wings operate in this nonintuitive way called Bernoulli’s Principle that states that the curved surface of the top of the wing causes the air to move faster and create negative pressure over the top of the wing which causes the wing to lift. Why in hell would anyone think such a thing when it obvious to any child that has ever stuck her hand straight out a car window how lift is created? The reason is that almost all school text books teach it and it is almost but not entirely wrong. One of the questions science teachers hate most is why airplanes can fly upside down if the top shape of the wing is so important.

You don’t need Bernoulli’s Principle to explain the basics of lift. The common sense way to teach it is that lift is created through the wing’s angle of attack by simple air deflection. You can make a flat wing that works just fine just by deflecting air at an angle. That is how they get planes to fly upside down. They hold the wing at an angle while the engine pulls the plane along. Air doesn’t just magically speed up to meet its air molecule friends on the other side when going through a shaped wing either. Bernoull’s Principle is a real effect that influences lift but telling people that aren’t aeronautical engineers about it is like skipping over addition and multiplication and diving straight into advanced calculus. It isn’t necessary for wings to work and should never be given as a primary explanation. Angle of attack is the primary cause of lift and the essential component to airplane flight across all of its control surfaces not Bernoulli’s Principle.

[elfkin477]

From having been asked by multiple people, I know that a small percentage of otherwise intelligent people are apparently laboring under the miconception that people who were born on Easter have a different birthdate every year. I’m always too shocked to think of asking them if they believe this applies to Thanksgiving babies too.

[Richard_Pearse]

Shagnasty, Bernoulli’s principle can explain ALL of the lift produced by a wing. Acceleration (not deflection) of the air downward can ALSO explain ALL of the lift produced by a wing. The shape of the upper surface of a wing is very important in how the wing accelerates (turns) the air downward, wings stall when airflow over the UPPER surface is disrupted, lift spoilers work by spoiling the flow of air over the UPPER surface. If you measure the volume and velocity of air accelerated downward and apply newton’s principles, you can account for the lift, if you also measure the velocities of air around the upper and lower surface of the wing and calculate the resulting pressures you can ALSO account for the lift of the wing.

There are two bad explanations of lift and you are mislead in thinking the bernoulli principle is one of them, you are also actually perpetuating the other one.

The first bad explanation is that of equal transit time, it says “a wing has a curved upper surface which means the air has further to travel over the top compared to the bottom, it must travel faster to meet the same bit of air that’s travelling across the bottom and pressure is therefore reduced.” This is wrong, the transit time is not equal, in fact the air flowing over the top of the wing gets to the trailing edge much sooner than the air going across the bottom.

The other bad explanation is that the air is deflected. It is not deflected. “Deflected” implies that the bottom surface of the wing is simply deflecting the air downwards, this is far from the whole story and is very misleading, the entire air mass the wing is travelling through, including the air over the top surface, is accelerated downward.

You bring up aircraft flying upside down, yes they can, but, speaking as someone who has spent a lot of time flying aeroplanes upside down, they don’t do it anywhere near as well as they do flying the right way up, and that is with a symmetrical airfoil, try flying a typical non-symmetrical airfoil upside down and they are very inefficient. Why? Because that curved upper wing surface is designed to accelerate air downward, when the thing is upside down it basically results in a fight between angle of attack and wing shape, the result is very poor performance. A much higher angle of attack is required to get the same amount of lift, the difference in velocities over the top and bottom are reduced, the pressure difference is also reduced, as is the amount of air being accelerated downward.

So to sum up, there are two bad explanations, both have a kernel of truth. The equal transit explanation is wrong, not because of Bernoulli, but because of the equal transit time part. The deflection explanation simply ignores the very important roll the upper surface of the wing plays.

You can use Bernoulli or Newton to explain lift, they are both equally as valid, and can both explain all of the lift produced, they are complimentary, both happening at the same time, both different ways of describing the same thing.

Please read this page for further education:

http://www.grc.nasa.gov/WWW/K-12/airplane/bernnew.html

[Throatwarbler_Mangrove]

@Shagnasty

A common misperception is that airplanes can fly because their wings operate in this nonintuitive way called Bernoulli’s Principle that states that the curved surface of the top of the wing causes the air to move faster and create negative pressure over the top of the wing which causes the wing to lift. Why in hell would anyone think such a thing when it obvious to any child that has ever stuck her hand straight out a car window how lift is created? The reason is that almost all school text books teach it and it is almost but not entirely wrong. One of the questions science teachers hate most is why airplanes can fly upside down if the top shape of the wing is so important.

You don’t need Bernoulli’s Principle to explain the basics of lift. The common sense way to teach it is that lift is created through the wing’s angle of attack by simple air deflection. You can make a flat wing that works just fine just by deflecting air at an angle. That is how they get planes to fly upside down. They hold the wing at an angle while the engine pulls the plane along. Air doesn’t just magically speed up to meet its air molecule friends on the other side when going through a shaped wing either. Bernoull’s Principle is a real effect that influences lift but telling people that aren’t aeronautical engineers about it is like skipping over addition and multiplication and diving straight into advanced calculus. It isn’t necessary for wings to work and should never be given as a primary explanation. Angle of attack is the primary cause of lift and the essential component to airplane flight across all of its control surfaces not Bernoulli’s Principle.

If the angle of the wing is so important, why can airplanes fly upside down?

[Malacandra]

@Throatwarbler_Mangrove

If the angle of the wing is so important, why can airplanes fly upside down?

Are you thinking that with the nose pointing at the horizon, the wing has a positive angle of attack when the plane’s right side up? It does (rigging angle), but that doesn’t stop you pointing the nose above the horizon to compensate while flying inverted. But for the rest, I’ll let my betters carry on.

[Simplicio]

@JohnT

He put direct quotes from the Pope coming out of the mouth of a guy named (in English) “Simpleton”.

That sort of shit gets you noticed, even today.

Aint nothin’ wrong with that.

[Richard_Pearse]

@Malacandra

Are you thinking that with the nose pointing at the horizon, the wing has a positive angle of attack when the plane’s right side up? It does (rigging angle), but that doesn’t stop you pointing the nose above the horizon to compensate while flying inverted. But for the rest, I’ll let my betters carry on.

Well that’s it in a nutshell. The angle of attack is the angle between the wing and the airflow, not the wing and the fuselage, so it is not reliant on being the right way up. It’s probably important to note that aeroplanes performing manoevers such as rolls and loops are normally maintaining a positive angle of attack throughout the manoever and are not proof that wings work upside down. You will normally only see specialised aerobatic aircraft and military aircraft maintaining sustained inverted flight. These aircraft have fuel and oil systems designed for inverted flight and typically, but not always, have wings designed to be a compromise between good upright performance and good inverted performance. They also have enough thrust to overcome the additional drag you tend to get when flying inverted.

[zagloba]

@elfkin477

From having been asked by multiple people, I know that a small percentage of otherwise intelligent people are apparently laboring under the miconception that people who were born on Easter have a different birthdate every year. I’m always too shocked to think of asking them if they believe this applies to Thanksgiving babies too.

That’s no more a misconception than that a person born on Feb 29 is one fourth the age of someone born the day before.

[Scribble]

Many people think that, when a genome gets sequenced, every single base pair of the sequence is known with complete certainty. They think that finding out part or all of an organism’s genome is like figuring out how much money is stuck under your couch cushions. In the case of cash in the couch, the hard part is getting at the money. Once you’ve got it in your hands, you can easily identify each coin and count up the total amount. Many people think that the hard part in getting a DNA sequence is getting at the DNA. Once you’ve got that, they reason, you can use some sort of fancy-schmancy technique to see exactly which bases you’ve got.

In reality, getting the DNA is usually the easy part. Figuring out which bases you have is the touchy part. Not only are there sequencing errors, but, even with DNA stretches where the sequencing is good, the person reading over the sequencing results often has to make a judgment call about some bases. Our lab makes copies of DNA by PCR and then sends out the DNA forSanger sequencing. Sequences come back with certainty ratings for each base read in the sequence. What your tolerance for uncertainty is affects how you interpret the sequence. I might accept a read that someone else would reject, because my standards for certainty are lower than the other person’s.

There are plenty of sequenced genomes or parts of genomes that have mistakes, uncorrected misreads, or bad judgement calls in them. Newer methods for sequencing DNA (pyrosequencing) can get you lower error rates, but there’s still a level of probability attached to each base determined.

[aruvqan]

@Scribble

Many people think that, when a genome gets sequenced, every single base pair of the sequence is known with complete certainty. They think that finding out part or all of an organism’s genome is like figuring out how much money is stuck under your couch cushions. In the case of cash in the couch, the hard part is getting at the money. Once you’ve got it in your hands, you can easily identify each coin and count up the total amount. Many people think that the hard part in getting a DNA sequence is getting at the DNA. Once you’ve got that, they reason, you can use some sort of fancy-schmancy technique to see exactly which bases you’ve got.

In reality, getting the DNA is usually the easy part. Figuring out which bases you have is the touchy part. Not only are there sequencing errors, but, even with DNA stretches where the sequencing is good, the person reading over the sequencing results often has to make a judgment call about some bases. Our lab makes copies of DNA by PCR and then sends out the DNA forSanger sequencing. Sequences come back with certainty ratings for each base read in the sequence. What your tolerance for uncertainty is affects how you interpret the sequence. I might accept a read that someone else would reject, because my standards for certainty are lower than the other person’s.

There are plenty of sequenced genomes or parts of genomes that have mistakes, uncorrected misreads, or bad judgement calls in them. Newer methods for sequencing DNA (pyrosequencing) can get you lower error rates, but there’s still a level of probability attached to each base determined.

See, this is exactly why I have serious trouble believing the scientists who claim we are totally not related to cro magnon man …

They extract a tiny bit of DNA, then have to putz around with it to make enough to work with, and the DNA may only be fragmentary … which to me states they do not have the entire compliment of DNA, so they are starting with a flawed set… so how do they know the bit they are missing? That missing bit may be the part that is related to us …

[Left_Hand_of_Dorkness]

@Tengu

Strawberries ARE fruit.

The master’s staff speaks

@SDStaff

The answer here seems to be that a strawberry is not really a berry, and may not be a fruit, depending on whom you ask.
…
The strawberry is the enlarged end of the plant stamen, although it is sometimes classified as an aggregate fruit (a fruit that develops from several ovaries of a single flower).

[flodnak]

@aruvqan

See, this is exactly why I have serious trouble believing the scientists who claim we are totally not related to cro magnon man …

Erm, nitpick? Cro-Magnon Man were not only related to us, they were us - Homo sapiens in a slightly earlier edition. I think you mean Neanderthal, and even in that case, no one seriously says they weren’t related to us at all. They were definitely Homo something, but there is a dispute about whether they should be classified as a subspecies of our species (Homo sapiens neanderthalensis) or a separate species (Homo neanderthalensis). At the moment the separate species argument is dominant. But even in that case, they were our biological cousins, very close indeed.

[Kamino_Neko]

@Left_Hand_of_Dorkness

The master’s staff speaks

Which is saying exactly what me and California Jobcase said - it’s a freaking fruit, unless you’re going to come up with some weird definition that excludes it because only part of the eaten part is actually the fruit.

[Left_Hand_of_Dorkness]

@Tengu

Which is saying exactly what me and California Jobcase said - it’s a freaking fruit, unless you’re going to come up with some weird definition that excludes it because only part of the eaten part is actually the fruit.

No, it’s not saying what you guys are saying. It’s saying that it can be considered a fruit or not a fruit. Personally, since the part that everyone thinks of as a strawberry–the red fleshy sweet part–doesn’t meet the definition of a fruit, I think it makes more sense botanically not to consider it a fruit.

[aruvqan]

@flodnak

Erm, nitpick? Cro-Magnon Man were not only related to us, they were us - Homo sapiens in a slightly earlier edition. I think you mean Neanderthal, and even in that case, no one seriously says they weren’t related to us at all. They were definitely Homo something, but there is a dispute about whether they should be classified as a subspecies of our species (Homo sapiens neanderthalensis) or a separate species (Homo neanderthalensis). At the moment the separate species argument is dominant. But even in that case, they were our biological cousins, very close indeed.

gah, neanderthal, you are right … that is what i get for posting before coffee … stayed up way too late playing LOTRO and have been running on 3 hours of sleep …

And I am quite adamant that they fully interbred with us, are an inseparable part of us. Hell, mrAru has a heavy brow ridge, and a bone crest, barrel chest and his arms armspan is longer than he is tall … if you stood him next to a full on skeleton in a display, the anthropologists in any crowd would figure he was part of the display some interns dressed in modern clothing as a joke [until he moved]

[Scribble]

@aruvqan

See, this is exactly why I have serious trouble believing the scientists who claim we are totally not related to cro magnon man …

They extract a tiny bit of DNA, then have to putz around with it to make enough to work with, and the DNA may only be fragmentary … which to me states they do not have the entire compliment of DNA, so they are starting with a flawed set… so how do they know the bit they are missing? That missing bit may be the part that is related to us …

Here are a few things you might find interesting. Warning: this reply is long, but it’s as short as I could make it without making it wrong.

1. All that “putzing around with the DNA to make enough to work with” is PCR. That technology is pretty solid. It was invented in the early 80s and has since become pretty standard, for use in everything from DNA fingerprinting and paternity tests to reconstructing the evolutionary history of the earliest living things.

2. To start finding the most likely evolutionary history of a group of related organisms, you really only need about 6 stretches of DNA that you can compare among those organisms. Of course, the more stretches of DNA you can use, the better your reconstruction of the group’s evolutionary history is likely to be.

But, in lots of cases, it just isn’t feasible to get whole genomes to work with. So you have a choice between two imperfect alternatives: you can try to reconstruct evolutionary history with what you have, pointing out that there’s some likelihood that you’re wrong; or you can decide not to do the work at all. Guess which alternative is usually more fruitful.

BTW–even if you did get whole genomes to work with, there would still be some uncertainty about the evolutionary history you reconstruct. You have to try to find the most likely evolutionary history, but that doesn’t mean that the most likely evolutionary history is necessarily what happened. Sometimes, even with lots of DNA, you get a most likely evolutionary history that isn’t that much more likely than another, radically different, evolutionary history.

When people publish reconstructed evolutionary histories in scientific journals, they’re usually careful to let everyone know how likely their reconstruction is, and which parts of the reconstructed history are more likely than others. When those same accounts get put into the popular press, those caveats usually get stripped away. That often leads people to think that, by some magic, scientists have figured out a full evolutionary past for something, with remarkably little evidence.

3. The “tiny bit of DNA” that sometimes gets extracted from a fossil or remnant is usually a set of pretty long sequences. There’s plenty of information in that DNA, but sometimes there aren’t enough molecules of those sequences to let you try to get at the information more than once or twice. Lots of times, things in the lab go wrong several times before you can get them to go right. If you’re working with living organisms, you can often go back for more DNA if you run out. If you’ve extracted DNA from a fossil or remnant, that’s often not an option.

In the case of DNA from fossil specimens, sometimes some of the DNA has degraded, but there’s still usually quite a bit of the sequence left. If you’re looking at fossil organisms that are closely related to living organisms with established genomes, you can usually tell which pieces of DNA are missing. You sequence the DNA you have from the fossil and compare it to the published genome. The pieces you have will line up nicely with specific stretches of DNA from the relative with the established genome. You can look between the lined-up pieces to see where the gaps are. For Cro-Magnons and modern humans, that would be pretty easy to do.

Also, individual molecules of fossil DNA will be degraded in different places, at random. So, if you have enough DNA from a fossil specimen, you can sequence many different molecules of that DNA, so that gaps in one molecule are covered by another.

[ITR_champion]

@zagloba

No, Florida has about 2000 American crocodiles, Crocodylus acutus, family Crocodylidae. On the other hand, in Florida alone there are between 1 and 1.5 million American alligators, Alligator mississippiensis, family Alligatoridae.

Okay, I was wrong about the no crocodiles in Florida business. So sue me.

[put_down_the_sabre]

@ITR_champion

Okay, I was wrong about the no crocodiles in Florida business. So sue me.

I believe the mission of this board is fighting ignorance. So no need for a lawsuit.

[fachverwirrt]

Legally blind is not 20/200. It is 20/200 with correction (there’s also a “field of vision” definition). My vision, for example, is about 20/800, but with contacts it’s 20/20 or better. So I am not legally blind.

[california_jobcase]

Some people think the upcoming Indianapolis 500 will happen in Indianapolis.

It won’t.

It will happen in Speedway, Indiana.