Things you were wrong about - 2021 Science Edition
August 7, 2021 5:10 PM Subscribe
I'm in my 50s, and thought I knew it all. In the past few weeks, I've learned that I was wrong (dead wrong!) about a couple of scientific "facts" that I had assumed were kind of "general knowledge" (for a certain nerdy sciencey kind of person).
Fact 1: When an aircraft crosses the speed of sound, there is a distrubance, and this distrubance is the sonic "boom". It happens once at that point. Actual fact: yes, there is a disturbance at the crossing, but that is not the sonic boom: once supersonic an aircraft makes a continual sonic boom that follows it everywhere it goes in a cone shape. "A sonic boom does not occur only at the moment an object crosses the speed of sound..."
Fact 2: Leaded gasoline protects engines, by some sort of coating or cooling mechanism on valve stems and seats, so you can't just remove lead from gasoline even if you were able to increase the octane number. Actual fact: it's really entirely about the anti-knock (anti-detonation) properties. Link
What other sciency general-knowledge "truths" did you (and presumably "everyone") believe in, that you realized were not true.
I'm mostly interested in ones that you learned about quite late in your life, where the incorrect understaning seems to be common: e.g. "common misconceptions".
Fact 1: When an aircraft crosses the speed of sound, there is a distrubance, and this distrubance is the sonic "boom". It happens once at that point. Actual fact: yes, there is a disturbance at the crossing, but that is not the sonic boom: once supersonic an aircraft makes a continual sonic boom that follows it everywhere it goes in a cone shape. "A sonic boom does not occur only at the moment an object crosses the speed of sound..."
Fact 2: Leaded gasoline protects engines, by some sort of coating or cooling mechanism on valve stems and seats, so you can't just remove lead from gasoline even if you were able to increase the octane number. Actual fact: it's really entirely about the anti-knock (anti-detonation) properties. Link
What other sciency general-knowledge "truths" did you (and presumably "everyone") believe in, that you realized were not true.
I'm mostly interested in ones that you learned about quite late in your life, where the incorrect understaning seems to be common: e.g. "common misconceptions".
Window glass does not flow, and any observations that the lower sections of windows in old buildings are thicker than the higher sections of the same windows are not due to the glass flowing.
posted by mr_roboto at 5:26 PM on August 7, 2021 [25 favorites]
posted by mr_roboto at 5:26 PM on August 7, 2021 [25 favorites]
Babies have object permanence younger than we thought. When you hide an object, it's not that they think the object has vanished from existence. They just don't have the executive functioning and motor planning abilities to pick up the blanket/cup/pillow/whatever you hid the object behind, so they start crying. You monster.
posted by brook horse at 5:27 PM on August 7, 2021 [46 favorites]
posted by brook horse at 5:27 PM on August 7, 2021 [46 favorites]
I actually have a pet peeve on this, which has me routinely screaming at podcasters, who repeat this untruth constantly (I'm looking at you, Rich Roll).
If you put a frog in boiling water, it will jump out. If you put it in tepid water and slowly raise the temperature, IT WIlL STILL JUMP OUT.
posted by FencingGal at 5:37 PM on August 7, 2021 [24 favorites]
If you put a frog in boiling water, it will jump out. If you put it in tepid water and slowly raise the temperature, IT WIlL STILL JUMP OUT.
posted by FencingGal at 5:37 PM on August 7, 2021 [24 favorites]
Goldfish do not have three-second memories. They can remember things for weeks, months, and even years.
posted by FencingGal at 5:39 PM on August 7, 2021 [19 favorites]
posted by FencingGal at 5:39 PM on August 7, 2021 [19 favorites]
I've been wrong about so many things it's hard to pick one. How about tourniquets? Everyone knew (and I taught for years) that applying a tourniquet pretty much guaranteed a limb would be lost, so it should only be done after all other methods to control bleeding had failed.
Actually tourniquets can be left on far longer than we thought without destroying the limb. (For 16 hours in one case.) And trying all those other methods first was a great way to waste time and allow life threatening bleeding to continue.
posted by wjm at 5:43 PM on August 7, 2021 [6 favorites]
Actually tourniquets can be left on far longer than we thought without destroying the limb. (For 16 hours in one case.) And trying all those other methods first was a great way to waste time and allow life threatening bleeding to continue.
posted by wjm at 5:43 PM on August 7, 2021 [6 favorites]
This Reddit thread from a month ago had people sharing what they learned too late in life. It’s not all science related, but it’s pretty darn funny and relatable.
posted by ejs at 5:49 PM on August 7, 2021 [6 favorites]
posted by ejs at 5:49 PM on August 7, 2021 [6 favorites]
Response by poster: Great answers, keep them coming! And to clarify, my comment above "ones you learned about late in life" -- I'm looking for "true facts" learned as a kid or young adult, where the falsity didn't come until much later.
posted by soylent00FF00 at 5:58 PM on August 7, 2021
posted by soylent00FF00 at 5:58 PM on August 7, 2021
There is no evidence that honeyguides actually lead honey badgers to honey. (They really do guide people to honey, though.)
posted by Redstart at 6:28 PM on August 7, 2021
posted by Redstart at 6:28 PM on August 7, 2021
The author of your linked page for Fact 2 seems like kind of a blowhard. It only took me about 30 seconds to find “scientific data” on valve seat recession.
posted by doctord at 7:19 PM on August 7, 2021 [3 favorites]
posted by doctord at 7:19 PM on August 7, 2021 [3 favorites]
The so-called "butterfly effect" is treated by many people as established fact, but it is entirely a myth. In reality, it is best understood as a thought experiment, an interesting "what if" exercise.
posted by yclipse at 7:54 PM on August 7, 2021 [4 favorites]
posted by yclipse at 7:54 PM on August 7, 2021 [4 favorites]
I was robbed of many decades of flavorful food because of the 80's-era advice on diet and health. In the 80's they blamed fat for everything, and the supermarket shelves were lined with rice-cakes and fat-free cream cheese.
Much too late, it came out that the sugar industry paid researchers to blame fat, at Harvard among others.
Also, the advice to run a calorie deficit to lose weight was also wrong. Humans don't process food by combustion like a bomb calorimeter. The Minnesota starvation experiment (using conscienscious objectors) had already shown that starvation causes obsession about food.
posted by dum spiro spero at 7:58 PM on August 7, 2021 [22 favorites]
Much too late, it came out that the sugar industry paid researchers to blame fat, at Harvard among others.
Also, the advice to run a calorie deficit to lose weight was also wrong. Humans don't process food by combustion like a bomb calorimeter. The Minnesota starvation experiment (using conscienscious objectors) had already shown that starvation causes obsession about food.
posted by dum spiro spero at 7:58 PM on August 7, 2021 [22 favorites]
Urine is sterile.
Sugar makes kids hyper.
Plastic shopping bags are horrible for the environment (they’re not great, but the standard alternatives of paper and cloth are worse).
posted by Betelgeuse at 8:05 PM on August 7, 2021 [6 favorites]
Sugar makes kids hyper.
Plastic shopping bags are horrible for the environment (they’re not great, but the standard alternatives of paper and cloth are worse).
posted by Betelgeuse at 8:05 PM on August 7, 2021 [6 favorites]
It is now known that lock washers don't "lock" anything and are essentially equivalent to a flat washer. Basically a waste of money and labour if you already have a flat washer or wouldn't benefit from a flat washer.. I know this and yet, sometimes, I still use [useless] lock washers "Just in Case".
I can tell you from personal experience with numerous used leaded gas engines (mostly V8 small and big block engines in light and medium duty applications but also /6 dodge in light and medium duty applications) converted to (no lead) LPG that lack of lead in LPG will wear the valve seats in to the point of performance degradation in about 60K kilometres and that doesn't happen with engines with hardened unleaded gas seats. Pull the heads and install hardened seats and you can get another 300k-400k out of those otherwise identical engines no problem.
This is in no way controversial in the LPG conversion community; it has been observed and documented 10s of thousands of times and I've read dead tree documentation regarding the issue from the LPG conversion companies. Though as with so much technical documentation produced pre internet I can't find any papers on line regarding it. (And the supply of leaded gas engines being converted has essentially dried up now anyways as most are at least 40 years old now making this mostly a moot point).
posted by Mitheral at 8:10 PM on August 7, 2021 [2 favorites]
I can tell you from personal experience with numerous used leaded gas engines (mostly V8 small and big block engines in light and medium duty applications but also /6 dodge in light and medium duty applications) converted to (no lead) LPG that lack of lead in LPG will wear the valve seats in to the point of performance degradation in about 60K kilometres and that doesn't happen with engines with hardened unleaded gas seats. Pull the heads and install hardened seats and you can get another 300k-400k out of those otherwise identical engines no problem.
This is in no way controversial in the LPG conversion community; it has been observed and documented 10s of thousands of times and I've read dead tree documentation regarding the issue from the LPG conversion companies. Though as with so much technical documentation produced pre internet I can't find any papers on line regarding it. (And the supply of leaded gas engines being converted has essentially dried up now anyways as most are at least 40 years old now making this mostly a moot point).
posted by Mitheral at 8:10 PM on August 7, 2021 [2 favorites]
That a randomized double-blinded controlled prospective trial is the one and only way to make medical decisions. For an example, read about the infant fish-oil (Omegaven) story.
posted by dum spiro spero at 8:24 PM on August 7, 2021 [9 favorites]
posted by dum spiro spero at 8:24 PM on August 7, 2021 [9 favorites]
Blood in your body is never blue, even when it is low in oxygen. It is an optical illusion that it looks that way under your skin. I learned this like 3 years ago. Link.
posted by Toddles at 8:44 PM on August 7, 2021 [10 favorites]
posted by Toddles at 8:44 PM on August 7, 2021 [10 favorites]
Didn’t find this out till a few months ago, but locusts are just what we call grasshoppers when they swarm.
Speaking of swarms, a “swarm of bees” always seemed like the most threatening agglomeration of our hymenopterid friends, but in fact bees are at their least aggressive when they’re swarming.
Sharks, obviously, not nearly as dangerous as we were led to believe.
No need to wait after eating before you swim.
Heavy metal doesn’t make people dangerous or delinquent. In fact they’re more likely to do well in school and be successful in life.
Carrots don’t contain inordinate amounts of vitamin A. At least not any more than other vegetables like spinach.
Apples, not particularly good for you. Mostly empty calories, although the fiber is helpful.
Cleopatra was closer to us historically than she was to the construction of the pyramids.
By Columbus’ time, it was well known that the earth was round.
We didn’t evolve from apes; we share a common ancestor.
posted by panama joe at 9:18 PM on August 7, 2021 [8 favorites]
Speaking of swarms, a “swarm of bees” always seemed like the most threatening agglomeration of our hymenopterid friends, but in fact bees are at their least aggressive when they’re swarming.
Sharks, obviously, not nearly as dangerous as we were led to believe.
No need to wait after eating before you swim.
Heavy metal doesn’t make people dangerous or delinquent. In fact they’re more likely to do well in school and be successful in life.
Carrots don’t contain inordinate amounts of vitamin A. At least not any more than other vegetables like spinach.
Apples, not particularly good for you. Mostly empty calories, although the fiber is helpful.
Cleopatra was closer to us historically than she was to the construction of the pyramids.
By Columbus’ time, it was well known that the earth was round.
We didn’t evolve from apes; we share a common ancestor.
posted by panama joe at 9:18 PM on August 7, 2021 [8 favorites]
The visible light spectrum was ROY G BIV - red, orange, yellow, green, blue, indigo, violet. Now it is either done in the same order but without indigo for a 6-colour spectrum, or: red, orange, yellow, green, cyan, blue, purple for a modern 7-colour spectrum.
I was also taught that Neanderthals were a stage of evolution for homo sapiens, a direct ancestor of modern humans, whereas now we consider them a different species or sub species that is extinct.
"dinosaurs are extinct" - now, it seems pretty accepted that birds are directly descended from some of the dinosaurs and we can no longer call them extinct in the way we we used to.
The appendix was known as a vestigial organ. It isn't.
posted by euphoria066 at 9:20 PM on August 7, 2021 [7 favorites]
I was also taught that Neanderthals were a stage of evolution for homo sapiens, a direct ancestor of modern humans, whereas now we consider them a different species or sub species that is extinct.
"dinosaurs are extinct" - now, it seems pretty accepted that birds are directly descended from some of the dinosaurs and we can no longer call them extinct in the way we we used to.
The appendix was known as a vestigial organ. It isn't.
posted by euphoria066 at 9:20 PM on August 7, 2021 [7 favorites]
The myth that there is some mystery about the mechanics of how bumblebees fly that can't be explained by conventional aerodynamics. It's just not true. Bumblebees flap their wings in a spinning pattern that creates the lift they need, it can be easily observed and explained by the science of aerodynamics.
The myth that shells, flowers, the human body, the Parthenon and other examples of classical art and architecture all display the Golden Mean ratio, which is uniquely aesthetically pleasing. It's all confirmation bias. All those objects also display any number of other ratios depending on how you measure them, and there is nothing uniquely beautiful about the Golden Mean as opposed to many other proportions.
The myth that being cold makes you susceptible to getting a cold or flu. It does not.
The myth that shaving hair makes it grow back darker or coarser.
The myths that wolves live in packs that are always vying for dominance, and are ruled over by the current "alpha" dominant wolf. And that dogs also display this behavior, so that you should "dominate" your dog in order to gain its respect. Wolves do have hierarchies, but the role of dominance and submission is much more subtle and complex than it's usually described as. Dogs are not wolves, and when it comes to training, they respond better to positive reinforcement.
posted by Zumbador at 9:32 PM on August 7, 2021 [16 favorites]
The myth that shells, flowers, the human body, the Parthenon and other examples of classical art and architecture all display the Golden Mean ratio, which is uniquely aesthetically pleasing. It's all confirmation bias. All those objects also display any number of other ratios depending on how you measure them, and there is nothing uniquely beautiful about the Golden Mean as opposed to many other proportions.
The myth that being cold makes you susceptible to getting a cold or flu. It does not.
The myth that shaving hair makes it grow back darker or coarser.
The myths that wolves live in packs that are always vying for dominance, and are ruled over by the current "alpha" dominant wolf. And that dogs also display this behavior, so that you should "dominate" your dog in order to gain its respect. Wolves do have hierarchies, but the role of dominance and submission is much more subtle and complex than it's usually described as. Dogs are not wolves, and when it comes to training, they respond better to positive reinforcement.
posted by Zumbador at 9:32 PM on August 7, 2021 [16 favorites]
We're often taught that many societies have, historically, eschewed drinking water in favor of beer, wine and other alcoholic drinks because of pathogens in the water.
Although it's always been understood that some water was good and some water was bad, and individuals have expressed strong reservations about consuming it, there's no evidence that it was avoided in any culture. There have been many reasons for drinking lots of alcohol throughout history -- such as the easy calories available from beer -- but fear of waterborne disease wasn't one of them.
posted by theory at 9:57 PM on August 7, 2021 [9 favorites]
Although it's always been understood that some water was good and some water was bad, and individuals have expressed strong reservations about consuming it, there's no evidence that it was avoided in any culture. There have been many reasons for drinking lots of alcohol throughout history -- such as the easy calories available from beer -- but fear of waterborne disease wasn't one of them.
posted by theory at 9:57 PM on August 7, 2021 [9 favorites]
tongue rolling ability and de/attached earlobes are mendelian characteristics, inherited in a predictable dominant/recessive way. Blue eyes are a recessive characteristic, so two blue eyed parents can't have a brown eyed child.
Nope. Turns out nearly all the 'fun mendelian quirks' you are taught to use in class to learn about mendelianism are myths http://udel.edu/~mcdonald/mythintro.html
posted by AFII at 3:17 AM on August 8, 2021 [9 favorites]
Nope. Turns out nearly all the 'fun mendelian quirks' you are taught to use in class to learn about mendelianism are myths http://udel.edu/~mcdonald/mythintro.html
posted by AFII at 3:17 AM on August 8, 2021 [9 favorites]
Raindrops are not tear-shaped.
Electricity does not take the path of least resistance.
posted by Rhomboid at 3:50 AM on August 8, 2021 [8 favorites]
Electricity does not take the path of least resistance.
posted by Rhomboid at 3:50 AM on August 8, 2021 [8 favorites]
Digital audio does not have 'stairsteps' from the sampling, and using higher sample rates does not make the sound more clear or remove artifacts by somehow 'filling in missing information between samples'.
posted by Rhomboid at 4:05 AM on August 8, 2021 [5 favorites]
posted by Rhomboid at 4:05 AM on August 8, 2021 [5 favorites]
Peeing on a jellyfish sting doesn’t deactivate the stingers or help at all, except possibly if you’re really hung over (dehydrated, with concentrated urine so that the urea helps the stingers detach).
Betelgeuse said urine isn’t sterile...
posted by jumanjinight at 4:12 AM on August 8, 2021 [1 favorite]
Betelgeuse said urine isn’t sterile...
posted by jumanjinight at 4:12 AM on August 8, 2021 [1 favorite]
We didn’t evolve from apes; we share a common ancestor.
Funny enough, we did descend from apes -- and, indeed, we are still apes -- just not from modern apes; e.g., chimpanzees or gorillas.
posted by nosewings at 4:19 AM on August 8, 2021 [6 favorites]
Funny enough, we did descend from apes -- and, indeed, we are still apes -- just not from modern apes; e.g., chimpanzees or gorillas.
posted by nosewings at 4:19 AM on August 8, 2021 [6 favorites]
Not so much something I was wrong about as much as something I hadn't thought of, never considered, and when I found out it really blew my mind, the universe is expanding faster than the speed of light.
posted by Rufous-headed Towhee heehee at 4:53 AM on August 8, 2021 [3 favorites]
posted by Rufous-headed Towhee heehee at 4:53 AM on August 8, 2021 [3 favorites]
Given the question, Rufous, that's an ironic takeaway and one the author takes care to disaffirm (i.e. it's a speed per distance).
posted by DeepSeaHaggis at 6:01 AM on August 8, 2021 [1 favorite]
posted by DeepSeaHaggis at 6:01 AM on August 8, 2021 [1 favorite]
Speaking of food, bananas aren't particularly high in potassium. Lots of foods have more.
And vegetarians and vegans don't have to think about combining proteins. This idea was started in the 1970s by the well-intentioned Frances Moore Lappe in her book Diet for a Small Planet. Lappe has repeatedly said she was wrong, but the myth persists, and even some dietitians still believe it. In fact, every whole food contains all essential amino acids, though some in trace amounts. If you don't believe me, you can check the USDA nutrient database.
posted by FencingGal at 6:05 AM on August 8, 2021 [7 favorites]
And vegetarians and vegans don't have to think about combining proteins. This idea was started in the 1970s by the well-intentioned Frances Moore Lappe in her book Diet for a Small Planet. Lappe has repeatedly said she was wrong, but the myth persists, and even some dietitians still believe it. In fact, every whole food contains all essential amino acids, though some in trace amounts. If you don't believe me, you can check the USDA nutrient database.
posted by FencingGal at 6:05 AM on August 8, 2021 [7 favorites]
Two cars going 45 mph who collide head on does not equate to 90 mph destruction (taught in school in the early 70s). It is still equivalent to a 45 mph head on collision with a brick wall.
posted by baegucb at 8:06 AM on August 8, 2021
posted by baegucb at 8:06 AM on August 8, 2021
“Decimate” means to reduce by a factor of 10. So when you hear someone say “that town was decimated by a flood” it’s not an accurate use of the term, instead it is being used to say “destroyed.”
posted by glaucon at 8:12 AM on August 8, 2021 [2 favorites]
posted by glaucon at 8:12 AM on August 8, 2021 [2 favorites]
enervate does not mean energized. It means the opposite. I got well into my thirties before I figured this out.
posted by philip-random at 8:21 AM on August 8, 2021 [3 favorites]
posted by philip-random at 8:21 AM on August 8, 2021 [3 favorites]
Two cars going 45 mph who collide head on does not equate to 90 mph destruction (taught in school in the early 70s). It is still equivalent to a 45 mph head on collision with a brick wall.
No, it's still worse than the brick wall.
A 90mph collision with an immovable object dissipates four times the energy of a 45mph collision because kinetic energy is proportional to the square of speed. A head-on between two cars of roughly the same size, each moving at 45mph, is not as bad as that but still involves roughly twice the crash energy of a 45mph immovable-object collision because each of the colliding cars contributes kinetic energy to the crash. This opens possibilities for destruction modes that wouldn't happen when driving into an immovable object at 45mph, depending on exactly how the dissipating crash energy gets distributed inside the colliding mess.
So if you're ever unfortunate enough to encounter a decision point where your only remaining options are (a) crash squarely into a massive concrete wall or (b) crash head-on into an approaching vehicle that's at least as big and fast as yours, pick (a) and brake like you've never braked in your life.
posted by flabdablet at 9:46 AM on August 8, 2021 [11 favorites]
No, it's still worse than the brick wall.
A 90mph collision with an immovable object dissipates four times the energy of a 45mph collision because kinetic energy is proportional to the square of speed. A head-on between two cars of roughly the same size, each moving at 45mph, is not as bad as that but still involves roughly twice the crash energy of a 45mph immovable-object collision because each of the colliding cars contributes kinetic energy to the crash. This opens possibilities for destruction modes that wouldn't happen when driving into an immovable object at 45mph, depending on exactly how the dissipating crash energy gets distributed inside the colliding mess.
So if you're ever unfortunate enough to encounter a decision point where your only remaining options are (a) crash squarely into a massive concrete wall or (b) crash head-on into an approaching vehicle that's at least as big and fast as yours, pick (a) and brake like you've never braked in your life.
posted by flabdablet at 9:46 AM on August 8, 2021 [11 favorites]
Gravity is not a force and in general you might find that YouTube channel interesting for other such "clarifications" of what you and I (in my 60's) were taught.
I heard this next one debunked when I was in my 20's, but almost every time I mention it folks are convinced I'm wrong and that the prevailing "truth" is correct (why does that sound familiar these days?):
Mirrors don't flip images left and right
posted by forthright at 10:19 AM on August 8, 2021 [3 favorites]
I heard this next one debunked when I was in my 20's, but almost every time I mention it folks are convinced I'm wrong and that the prevailing "truth" is correct (why does that sound familiar these days?):
Mirrors don't flip images left and right
posted by forthright at 10:19 AM on August 8, 2021 [3 favorites]
The oldest meaning of decimate is reduce by 10% rather than reduce to 10%, but here's a more complete discussion.
A lot of forensic techniques made famous by CSI and the likes, like bloodspatter analysis, don't have much, if any, scientific basis. And they're used in actual real-life court cases nevertheless. Here's a good podcast episode (last part of a three-part series) about it.
I learned (and believed) that biological sex is binary: your DNA has either XX and XY chromosomes, and that's it. Another podcast episode taught me that it is much more complicated, you can have XXY, XXX, XXYY chromosomes and other variations. And you can even have XX and XY chromosomes in the same body!
posted by snusmumrik at 10:49 AM on August 8, 2021 [7 favorites]
A lot of forensic techniques made famous by CSI and the likes, like bloodspatter analysis, don't have much, if any, scientific basis. And they're used in actual real-life court cases nevertheless. Here's a good podcast episode (last part of a three-part series) about it.
I learned (and believed) that biological sex is binary: your DNA has either XX and XY chromosomes, and that's it. Another podcast episode taught me that it is much more complicated, you can have XXY, XXX, XXYY chromosomes and other variations. And you can even have XX and XY chromosomes in the same body!
posted by snusmumrik at 10:49 AM on August 8, 2021 [7 favorites]
I learned that encephalitis lethargica -- the Oliver Sacks Awakenings disease -- was an aftereffect of the flu pandemic. This is unlikely. The timing doesn't actually line up, and the case for a tie to influenza is not compelling. There's suggestive evidence towards an enterovirus.
posted by away for regrooving at 11:28 AM on August 8, 2021 [1 favorite]
posted by away for regrooving at 11:28 AM on August 8, 2021 [1 favorite]
Panda bears are not more closely related to racoons than to actual bears (what I learned in school)... they are in fact taxonomically more closely related to bears. Red pandas, however, are more closely related to raccoons.
posted by honeybee413 at 12:23 PM on August 8, 2021 [1 favorite]
posted by honeybee413 at 12:23 PM on August 8, 2021 [1 favorite]
Best answer: This is a terrific classic MetaFilter thread that is somewhat related: "You were doing it wrong: What in life did it take you a surprisingly long time to realize you've been doing wrong all along?"
posted by Conrad Cornelius o'Donald o'Dell at 1:17 PM on August 8, 2021 [1 favorite]
posted by Conrad Cornelius o'Donald o'Dell at 1:17 PM on August 8, 2021 [1 favorite]
Best answer: Wikipedia has a page for this: List of common misconceptions
posted by O9scar at 1:40 PM on August 8, 2021
posted by O9scar at 1:40 PM on August 8, 2021
Hot air doesn't "hold" more water.
posted by klangklangston at 1:52 PM on August 8, 2021
posted by klangklangston at 1:52 PM on August 8, 2021
Hot air doesn't "hold" more water
Please elaborate. I've survived a few thermodynamics courses and this is a thing I think is true. I won't pretend I excelled in those courses, but I don't have any other way to explain dew.
posted by Acari at 3:47 PM on August 8, 2021
Please elaborate. I've survived a few thermodynamics courses and this is a thing I think is true. I won't pretend I excelled in those courses, but I don't have any other way to explain dew.
posted by Acari at 3:47 PM on August 8, 2021
Unless the "air" is the key, in which case okay, pretend I said nothing (just air is kind of omnipresent)
posted by Acari at 3:49 PM on August 8, 2021
posted by Acari at 3:49 PM on August 8, 2021
I'm going to push back against a couple of these.
Gravity is not a force
Yes, general relativity uses spacetime curvature rather than a Newtonian mass-acceleration relationship to describe gravitation. In practical terms, though, gravity is almost always treated as a force. For instance, when we formulate the governing equations for fluid mechanics, gravity is included as a body force term, resulting an an acceleration proportional to the mass of a differential fluid element. This treatment of gravity as a force is pretty much universal across engineering disciplines, as well as most branches of physics, astronomy, geophysics, etc. with exceptions for the study of unusual gravitational phenomena like neutron stars, black holes, and gravity waves. The distinction between "force" and "not a force" is an ontological question that really has no practical implications. When it comes down to brass tacks, Newton's Second Law is the big game, and gravity represents a force term.
Hot air doesn't "hold" more water.
It's not clear what you mean here, but there's no question that the vapor pressure of water depends on temperature: at higher temperatures, at equilibrium, there will be more water in the vapor phase.
posted by mr_roboto at 4:40 PM on August 8, 2021 [8 favorites]
Gravity is not a force
Yes, general relativity uses spacetime curvature rather than a Newtonian mass-acceleration relationship to describe gravitation. In practical terms, though, gravity is almost always treated as a force. For instance, when we formulate the governing equations for fluid mechanics, gravity is included as a body force term, resulting an an acceleration proportional to the mass of a differential fluid element. This treatment of gravity as a force is pretty much universal across engineering disciplines, as well as most branches of physics, astronomy, geophysics, etc. with exceptions for the study of unusual gravitational phenomena like neutron stars, black holes, and gravity waves. The distinction between "force" and "not a force" is an ontological question that really has no practical implications. When it comes down to brass tacks, Newton's Second Law is the big game, and gravity represents a force term.
Hot air doesn't "hold" more water.
It's not clear what you mean here, but there's no question that the vapor pressure of water depends on temperature: at higher temperatures, at equilibrium, there will be more water in the vapor phase.
posted by mr_roboto at 4:40 PM on August 8, 2021 [8 favorites]
Response by poster: Interesting about the tetraethyl lead controversy - maybe my misconception was right?
Perhaps that's worth a new ask "What thing did you confidently know was correct, later learn to be false, and later later learn to actually have been correct"?
Two more I just thought about:
* Salt: you don't salt water when making pasta so the water boils faster (or hotter). You salt it because salt tastes good and maybe changes the texture of the cooked noodle. Yes, salt does slighltly change the boiling point, but that's noise compared to the taste factor.
* Higher tire pressure is alwas more energy efficient: Nope
posted by soylent00FF00 at 4:52 PM on August 8, 2021
Perhaps that's worth a new ask "What thing did you confidently know was correct, later learn to be false, and later later learn to actually have been correct"?
Two more I just thought about:
* Salt: you don't salt water when making pasta so the water boils faster (or hotter). You salt it because salt tastes good and maybe changes the texture of the cooked noodle. Yes, salt does slighltly change the boiling point, but that's noise compared to the taste factor.
* Higher tire pressure is alwas more energy efficient: Nope
posted by soylent00FF00 at 4:52 PM on August 8, 2021
I don't think I was that old when I had my misconception corrected, but it's an incredibly common misconception still among even many experts in my field:
"Negative reinforcement" is not a synonym for "punishment". In the terminology of learning theory, "reinforcement' is anything that causes an animal (or person) to learn to do more of something, and "punishment" is anything that causes an animal (or person) to learn to do less of it. Negative reinforcement is actually a way to get someone to do more of whatever it is they're doing! In this context, "positive" and "negative" refer to the addition or removal of a stimulus. For example, if there's some kind of obnoxious sound that is playing and you really hate it, and I take that away, that could serve as a negative reinforcer to get you to do something.
Often when people say "negative reinforcement," they really mean "punishment," which is confusing because punishment can also come in positive (adding something) and negative (removing something) forms.
posted by biogeo at 12:51 AM on August 9, 2021 [1 favorite]
"Negative reinforcement" is not a synonym for "punishment". In the terminology of learning theory, "reinforcement' is anything that causes an animal (or person) to learn to do more of something, and "punishment" is anything that causes an animal (or person) to learn to do less of it. Negative reinforcement is actually a way to get someone to do more of whatever it is they're doing! In this context, "positive" and "negative" refer to the addition or removal of a stimulus. For example, if there's some kind of obnoxious sound that is playing and you really hate it, and I take that away, that could serve as a negative reinforcer to get you to do something.
Often when people say "negative reinforcement," they really mean "punishment," which is confusing because punishment can also come in positive (adding something) and negative (removing something) forms.
posted by biogeo at 12:51 AM on August 9, 2021 [1 favorite]
In music theory: At no point in history did any society believe that a tritone interval was The Devil's Interval or would summon the Devil.
posted by mmoncur at 3:07 AM on August 9, 2021 [3 favorites]
posted by mmoncur at 3:07 AM on August 9, 2021 [3 favorites]
"Please elaborate. I've survived a few thermodynamics courses and this is a thing I think is true. I won't pretend I excelled in those courses, but I don't have any other way to explain dew."
It's not clear what you mean here, but there's no question that the vapor pressure of water depends on temperature: at higher temperatures, at equilibrium, there will be more water in the vapor phase."
The air doesn't hold anything. The temperature/pressure interaction of molecular forces functions roughly the same in a vacuum as it does on earth. Dry air is actually heavier than humid air, because equal volumes of gas at the same temperature and pressure contain the same number of molecules (Avogadro's Law), and water has a lower molecular weight than the nitrogen and oxygen it displaces.
The equilibrium vapor point — dew point, basically — is the temperature/pressure combination where an equal amount of water molecules will be transitioning to liquid or vapor (below that point, it condenses as dew; above that, liquid evaporates to vapor). Higher temperatures have a higher proportion of vapor to liquid at equilibrium. This is a physical property of liquids and gasses; water is generally the only one we care about in day to day life.
Relative humidity is the proportion of current vapor pressure to equilibrium vapor pressure, but the liquid metaphor of solute/solution is wrong for gasses — the saturation point of water vapor is entirely a function of the water vapor's temperature and pressure, specifically the molecular attraction forces against the molecular kinetic energy.
Bad Metereology explanation, Washington Post, Scientific American, Reddit AskScience.
posted by klangklangston at 11:08 AM on August 9, 2021
It's not clear what you mean here, but there's no question that the vapor pressure of water depends on temperature: at higher temperatures, at equilibrium, there will be more water in the vapor phase."
The air doesn't hold anything. The temperature/pressure interaction of molecular forces functions roughly the same in a vacuum as it does on earth. Dry air is actually heavier than humid air, because equal volumes of gas at the same temperature and pressure contain the same number of molecules (Avogadro's Law), and water has a lower molecular weight than the nitrogen and oxygen it displaces.
The equilibrium vapor point — dew point, basically — is the temperature/pressure combination where an equal amount of water molecules will be transitioning to liquid or vapor (below that point, it condenses as dew; above that, liquid evaporates to vapor). Higher temperatures have a higher proportion of vapor to liquid at equilibrium. This is a physical property of liquids and gasses; water is generally the only one we care about in day to day life.
Relative humidity is the proportion of current vapor pressure to equilibrium vapor pressure, but the liquid metaphor of solute/solution is wrong for gasses — the saturation point of water vapor is entirely a function of the water vapor's temperature and pressure, specifically the molecular attraction forces against the molecular kinetic energy.
Bad Metereology explanation, Washington Post, Scientific American, Reddit AskScience.
posted by klangklangston at 11:08 AM on August 9, 2021
The air doesn't hold anything.
I think this is a matter of semantics. The problem with saying "Hot air doesn't 'hold' more water" is that it seems to imply that the concentration (mole fraction, partial pressure, etc.) of water in the atmosphere doesn't change with temperature, which is not the case. The phrasing is semantically fraught and should be avoided--for instance, it seems to be making a distinction between "air" and "water" while water vapor is of course a component of air. And "hold" is pretty meaningless in this context.
posted by mr_roboto at 12:17 PM on August 9, 2021 [2 favorites]
I think this is a matter of semantics. The problem with saying "Hot air doesn't 'hold' more water" is that it seems to imply that the concentration (mole fraction, partial pressure, etc.) of water in the atmosphere doesn't change with temperature, which is not the case. The phrasing is semantically fraught and should be avoided--for instance, it seems to be making a distinction between "air" and "water" while water vapor is of course a component of air. And "hold" is pretty meaningless in this context.
posted by mr_roboto at 12:17 PM on August 9, 2021 [2 favorites]
Related: you can't make a clothes dryer more efficient just by running the interior at lower atmospheric pressure.
posted by flabdablet at 12:31 PM on August 9, 2021
posted by flabdablet at 12:31 PM on August 9, 2021
Peeing on a jellyfish sting doesn’t deactivate the stingers or help at all, except possibly if you’re really hung over (dehydrated, with concentrated urine so that the urea helps the stingers detach).
Interestingly, a piece of "common knowledge" that I believed, but recently learned is false is the belief that drinking alcoholic drinks dehydrates you. It does not, and therefore hangovers are not caused by dehydration. While alcohol makes you urinate more, this is more than canceled out by the water in alcoholic drinks. This goes for normal alcoholic drinks. Pure 100% ABV alcohol contains no water, so it will cause net dehydration. Very strong drinks like 80% absinthe possibly do as well, but I'd wager the amount you would need to drink to get noticeably dehydrated from those would cause more significant problems in other ways.
This also applies to caffeine and caffeinated drinks like coffee. Contrary to what I had heard, it does not seem to dehydrate you.
Of course, the idea that it is so easy to get dehydrated, and that we need to drink lots of water to avoid it is itself also a myth. Drink when you are thirsty, and stop when you're not.
posted by Spiegel at 3:23 PM on August 9, 2021 [3 favorites]
Interestingly, a piece of "common knowledge" that I believed, but recently learned is false is the belief that drinking alcoholic drinks dehydrates you. It does not, and therefore hangovers are not caused by dehydration. While alcohol makes you urinate more, this is more than canceled out by the water in alcoholic drinks. This goes for normal alcoholic drinks. Pure 100% ABV alcohol contains no water, so it will cause net dehydration. Very strong drinks like 80% absinthe possibly do as well, but I'd wager the amount you would need to drink to get noticeably dehydrated from those would cause more significant problems in other ways.
This also applies to caffeine and caffeinated drinks like coffee. Contrary to what I had heard, it does not seem to dehydrate you.
Of course, the idea that it is so easy to get dehydrated, and that we need to drink lots of water to avoid it is itself also a myth. Drink when you are thirsty, and stop when you're not.
posted by Spiegel at 3:23 PM on August 9, 2021 [3 favorites]
"Also, the advice to run a calorie deficit to lose weight was also wrong. Humans don't process food by combustion like a bomb calorimeter. The Minnesota starvation experiment (using conscienscious objectors) had already shown that starvation causes obsession about food.
posted by dum spiro spero"
Why is it wrong to think that running a calorie deficit makes you lose weight? The experiment may have shown that starvation causes obsession about food, but what does that have to do with initial weight loss? If you're saying that food obsession makes it likely you'll gain the weight back, that's irrelevant. The subjects in that experiment did lose the weight via calorie deficit, which is the issue.
posted by DMelanogaster at 3:55 AM on August 12, 2021 [2 favorites]
posted by dum spiro spero"
Why is it wrong to think that running a calorie deficit makes you lose weight? The experiment may have shown that starvation causes obsession about food, but what does that have to do with initial weight loss? If you're saying that food obsession makes it likely you'll gain the weight back, that's irrelevant. The subjects in that experiment did lose the weight via calorie deficit, which is the issue.
posted by DMelanogaster at 3:55 AM on August 12, 2021 [2 favorites]
In practical terms, though, gravity is almost always treated as a force.
In practical terms it is a force.
I think the distinction being made, is that it's not a fundamental force. It's an emergent phenomena resulting from the temporal gradient exerted by objects with mass.
Adjacent objects exerting a temporal gradient will move to a lower energy state, i.e. closer together, and this is what we experience as a force. This is also why, unlike the fundamental forces, gravity does not have parity.
posted by HiroProtagonist at 9:11 PM on August 12, 2021
In practical terms it is a force.
I think the distinction being made, is that it's not a fundamental force. It's an emergent phenomena resulting from the temporal gradient exerted by objects with mass.
Adjacent objects exerting a temporal gradient will move to a lower energy state, i.e. closer together, and this is what we experience as a force. This is also why, unlike the fundamental forces, gravity does not have parity.
posted by HiroProtagonist at 9:11 PM on August 12, 2021
Heavy metal doesn’t make people dangerous or delinquent. In fact they’re more likely to do well in school and be successful in life
Is that supposed to refer to heavy metal music or something? Because heavy metal poisoning is associated with a lot of poor health outcomes, including death...
posted by yohko at 7:14 PM on August 13, 2021 [1 favorite]
Is that supposed to refer to heavy metal music or something? Because heavy metal poisoning is associated with a lot of poor health outcomes, including death...
posted by yohko at 7:14 PM on August 13, 2021 [1 favorite]
Response by poster: For fun, I made a new Ask: Things you were wrong about being wrong about
posted by soylent00FF00 at 4:49 PM on August 21, 2021
posted by soylent00FF00 at 4:49 PM on August 21, 2021
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posted by mr_roboto at 5:19 PM on August 7, 2021 [22 favorites]