Home » Teaching
Category Archives: Teaching
What’s the difference between geometry, geology, geography and geodesy?
the branch of mathematics concerned with the properties and relations of points, lines, surfaces, solids.
and of course geometry has many practical uses in many careers, such as building gears, drills bits, laying out camera lenses, and so much more.
the science that deals with the earth’s physical structure and substance, its history, and the processes that act on it.
Which includes the study of minerals, crystals and rocks.
the spatial study of Earth’s landscapes, peoples, places and environments. This includes cartography (map-making.)
There are many types of maps used in geography.
Geodesy combines applied mathematics and earth sciences to measure and represent the Earth (or any planet.)
from the National Oceanic and Atmospheric Administration Ocean Service Education page on Geodesy:
Geodesists basically assign addresses to points all over the Earth. By looking at the height, angles, and distances between these locations, geodesists create a spatial reference system that everyone can use.
Building roads and bridges, conducting land surveys, and making maps are some of the important activities that depend on a spatial reference system.
For example, if you build a bridge, you need to know where to start on both sides of the river. If you don’t, your bridge may not meet in the middle.
As positioning and navigation have become fundamental to the functions of society, geodesy has become increasingly important.
Precise Geodetic Infrastructure: National Requirements for a Shared Resource (2010) – Geodesy for the Benefit of Society
Seismic waves are waves of energy that travel through the Earth’s layers.
They are a result of earthquakes, volcanic eruptions, magma movement, large landslides and large man-made explosions.
They are studied by geophysicists called seismologists.
They are recorded by a seismometer/ seismograph, a hydrophone (when in water), or by an accelerometer.
Water waves are an example
Rayleigh surface waves
“The Rayleigh surface waves are the waves that cause the most damage during an earthquake. They travel with velocities slower than S waves, and arrive later, but with much greater amplitudes. These are also the waves that are most easily felt during an earthquake and involve both up-down and side-to-side motion.”
How do we measure motions of the Earth?
What is a seismograph?
Intro to be written
This is a seismograph record.
Many forces can act on tectonic plates, on mountains, even on individual rocks. Those rocks usually stay together as one piece, because the atoms and molecules are holding each other with strong bonds.
If a force becomes stronger than the bonds holding the rock together then the rock breaks apart. It will cleave or fracture.
Cleavage planes form along the weakest area of mineral’s structure.
These breaks create flat, planar surfaces.
These surfaces are determined by the structure of its crystal lattice.
These cleavage planes are smooth and are usually reflective.
Note – If a mineral’s structure is equally strong in all directions then it will not have cleavage planes – then it will show fracture (see next section.)
Mica has 1d cleavage
Fluorite octahedral cleavage
Calcite has rhombohedral cleavage.
If a mineral’s structure is equally strong in all directions then it will not have cleavage planes. Then it will just break unevenly.
Fractures have no definite shape.
Chrysotile has splintery fracture.
Quartz has conchodial fracture
Obsidian conchoidal fracture
Limonite, bog iron ore, earthy fracture
Crystals of native copper Hackly fracture (jagged fracture)
Magnetite uneven fracture
Samples with both cleavage and fracture
Cleavage and fracture in potassium feldspar
Cleavage terms (only use if cleavage planes can be recognized):
Perfect – Produces smooth surfaces (often seen as parallel sets of straight lines), e.g. mica;
Imperfect – Produces planes that are not smooth, e.g. pyroxene;
Poor – Less regular.
Fracture terms (use in all other cases):
Conchoidal – Fracture surface is a smooth curve, bowl-shaped (common in glass);
Hackly – Fracture surface has sharp, jagged edges;
Uneven – Fracture surface is rough and irregular;
Fibrous – Fracture surface shows fibres or splinters.
This section from
You’ve heard of “laws of nature.” What are they?
Well, let’s start with the word “law: – what does it mean? Don’t shoot the messenger, but the same word sometimes means very different things. And this matters in science, especially when it comes to the “laws of nature.”
In ELA class you’ve hopefully learned about homographs – words spelled the same but have different meanings. For instance, what is a “bow?”
bow – noun, the front of a boat
bow – verb, to bend at the waist.
bow – noun, a type of ribbon we used to decorate a present.
bow – noun, sporting equipment used to shoot arrows.
Wow, so all of these look and sound the same, yet they are entirely different words! Well, the same is true for the word “law.” It can refer to three different things:
* law, as in laws are made up by people, laws passed by governments
* law, as in natural law
* law, as in a law of nature
And all three of these things have nothing to do with each other! Let’s look at all three of these carefully:
* “Law,” as in laws are made up by people, and passed by governments, aren’t actually “real” in any scientific sense. They aren’t part of the universe. They aren’t universally agreed on. And they don’t stay the same. They change all the time.
How old does one have to be in order to vote? How fast can you drive a car on the road? How much property tax does a homeowner have to pay on a house? None of those rules are part of the universe. These “laws”are just things that people agree on. Nothing more. People get together in communities or groups, they create clubs, or governments, and they make up rules so that (hopefully) society runs safely and smoothly. So in this sense, “law” means “a rule that, for now, our community has decided to follow.”
* “Law,” as in natural law, is a belief that many people hold: there are universal moral laws in nature that mankind is capable of learning, and obligated to follow.
This idea is held by some religious groups and some schools of philosophy. It isn’t necessarily related to religion; there are many non-religious people who believe in the necessary existence of natural law.
* “Law,” as in a law of nature, again is totally different from the other terms. Laws of nature are what we learn about in physics! In science, a “law” of nature is a rule for how things in the physical world work. Humans don’t decide what these laws are. Rather, we investigate the universe and discover what they are.
-> Laws of nature are factual truths, not logical. For instance, electrical charge is conserved – the total electric charge in an isolated system never changes. We can’t pass a law that says “positive charges can now be created.” Won’t work. Nothing humans say will change the way that the universe works,
-> Laws of nature are true for every time and every place. They are just as true on the moon, Mars as on Earth. They are just as true in Boston, Tokyo, or Kiev. And just as true 10,000 years ago as today, and as next year.
There is some kind of process that builds mountains, but there also must be something limiting that process. After all, we don’t see mountains 20 or 30 miles tall, right? So we must ask, how high can a mountain grow?
We start by asking, what are the highest mountains on Earth?
Which then brings up the next question, what do we mean by “highest”? The answer isn’t obvious because there are three different ways to think about “highest” – see this diagram.
Given this, we next notice that most mountains on Earth are nowhere near this height. For instance, the highest mountain in New England is Mount Washington New Hampshire 1,900 m (6,300 ft.). The highest mountain in the Rocky Mountains in Mount Elbert in Colorado 4400 m (14,000 ft.)
In general, almost everywhere on our planet, the highest that a mountain can be is about half the height of Everest. This is as tall as a mountain can grow on a lithospheric tectonic plate.
So our next question is, “why is there one set of rules for the highest that a mountain can be almost everywhere on Earth, and why do some locations have exceptions?”
What factors control the height of a mountain?
There is a balance of the forces:
Tectonic plate forces pushes the Earth’s crust upward.
Gravity pulls the mountain downward.
And, when the mountain is high & big enough, the weight of the mountain can crack and shatter the rock inside of it. This causes the mountain to crumble, and settle down to a lower height.
Don’t believe me? Even rock has a maximum amount of strength. Here is a GIF of what happens to solid rock when you put enough pressure on it! 🙂
Thus, if the weight of mountain > yield strength of the base rock then the mountain’s base will crumble.
Then he mountain will compress down to the maximum allowable height.
Of course, when this happens depends on what the mountain is made of. SiO2 is the most common molecule. But there are many minerals that are lighter, or stronger, or both, that can also be found in a mountain.
By the way, this gives us a neat relation – the surface gravity X maximum height of a mountain should be a constant.
Formula lets us relate height of Mt Everest on earth and Olympus Mons on Mars. Or find max deformation of asteroid before gravity pulls it into a sphere.
All the other downward forces on a mountain
Erosion wears the mountain down
How well does the mountain resist weathering/erosion? This depends on what kind of chemicals it is made out of.
Does being in the ocean affect how high a mountain can be?
Consider Mauna Kea, in Hawaii.
Much of Mauna Kea is underwater. It’s base can support more pressure since it’s underwater. Underwater, there is a buoyant force on the object that counteracts the force of gravity. Since nothing counteracts the gravity on Mount Everest, the mountain’s base can only support so much pressure.
What else makes mountains rise or grow?
Even while a mountain is eroding, the underlying plate activity may be forcing the mountain to grow higher.
A tectonic plate pushing more directly against another plate will create higher mountains than a plate moving less directly (say, at an angle) against another plate.
How strong are the crustal roots of the mountain?
As a mountain range grows in height, this root grows in depth, and thus the pressure and temperature experienced by the bottom of this root increases.
At a certain point, rocks in the base of this crustal root metamorphose into a rock called eclogite. At that point this rock will be denser than the material supporting the crustal root.
This causes delamination to occur. Depending on the amount of material removed, the rate of new material added, and erosion, scenarios with net increases or decreases in elevation are possible after a delamination event. This sets another limit on how thick a crustal root can get (and thus how high a mountain range grow on the long term).
Why are there some special spots on Earth where mountains can grow twice as high?
George W Hatcher writes
Mauna Kea rests on oceanic crust, which is denser than continental crust and able to support more weight without displacement. Being mostly inundated with seawater precludes some of the erosional processes to which mountains exposed to the upper atmosphere are subjected.
In addition, the very material of which Mauna Kea is composed (basaltic igneous rocks) is stronger than the variety of rocks that make up the continental crust and uplifted limestone seafloor that can be found atop Everest.
The actual lithospheric limit to mountain height averages about half the height of Everest, which is why Fourteeners are so famous in Colorado. Mountains that exceed this limit have local geologic circumstances that make their height possible, e.g. stronger or denser rocks.
In the case of Everest and the Himalayas, you have a geologic situation that is very rare in Earth history. The Indian plate is ramming into the Eurasian plate with such force that instead of just wrinkling the crust on either side into mountain ranges it has actually succeeded in lifting the Eurasian plate up on top.
So the Himalayas have double the thickness of the average continental plate, thus double the mountain height that would be considered “normal”.
Examples with math details
Related lab ideas
Maslow’s hierarchy of needs is a theory in psychology proposed by Abraham Maslow. His first discussion of this idea was in his 1943 paper “A Theory of Human Motivation” in Psychological Review. It was developed further in his 1954 book Motivation and Personality.
Contrary to popular belief, Maslow never created a pyramid to represent these needs. Nor did he conclude that in order for motivation to arise at the next stage, each stage must be satisfied. Much that teachers have heard about Maslow’s hierarchy of needs isn’t what he taught.
How his ideas were changed, incorrectly claimed as scientifically proven, and then became the basis of profitable seminars in business and education, is the subject of these papers:
Who Built Maslow’s Pyramid? A History of the Creation of Management Studies’ Most Famous Symbol and Its Implications for Management Education, by Todd Bridgman, Stephen Cummings and John Ballard, Academy of Management Learning & EducationVol. 18, No. 1, 3/1/2019
“Who Created Maslow’s Iconic Pyramid?” by Scott Barry Kaufman Scientific American, 4/23/2019
Even today the popular packaging of Maslow’s work is popular in management training and secondary and higher psychology and education instruction.
Saul McLeod points out that
Maslow continued to refine his theory based on the concept of a hierarchy of needs over several decades. Regarding the structure of his hierarchy, Maslow proposed that the order in the hierarchy “is not nearly as rigid” as he may have implied in his earlier description. Maslow noted that the order of needs might be flexible based on external circumstances or individual differences. For example, he notes that for some individuals, the need for self-esteem is more important than the need for love. For others, the need for creative fulfillment may supersede even the most basic needs.
Maslow’s Hierarchy of Needs, 3/20/2020, Saul McLeod, Simply Psychology
In Scientific American, Scott Barry Kaufman writes
Abraham Maslow’s iconic pyramid of needs is one of the most famous images in the history of management studies. At the base of the pyramid are physiological needs, and at the top is self-actualization, the full realization of one’s unique potential. Along the way are the needs for safety, belonging, love, and esteem.
However, many people may not realize that during the last few years of his life Maslow believed self-transcendence, not self-actualization, was the pinnacle of human needs. What’s more, it’s difficult to find any evidence that he ever actually represented his theory as a pyramid.
On the contrary, it’s clear from his writings that he did not view his hierarchy of needs like a video game– as though you reach one level and then unlock the next level, never again returning to the “lower” levels. He made it quite clear that we are always going back and forth in the hierarchy, and we can target multiple needs at the same time.
If Maslow never built his iconic pyramid, who did? In a recent paper, Todd Bridgman, Stephen Cummings, and John Ballard trace the true origins of the pyramid in management textbooks, and lay out the implications for the amplification of Maslow’s theory, and for management studies in general. In the following Q & A, I chat with the authors of that paper about their detective work.
Question: Why did you set out to answer the question: Who built “Maslow’s Pyramid”?
My colleague Stephen Cummings and I have long been interested in how foundational ideas of our field, management studies, are represented in textbooks. Textbooks often present ideas very differently than in the original writings. We’re interested in understanding how and why this happens. We’ve taught Maslow’s hierarchy of needs for many years and were aware the pyramid did not appear in his most well-known works, so were interested in delving deeper. We contacted John Ballard, who knew Maslow’s work better than we did and who shared our concern about Maslow’s theory being misrepresented. Thankfully, he agreed to join us on the project.
Question: Do you think the popularity of Maslow’s hierarchy of needs is due in part to the iconic appeal of the pyramid that became associated with it?
Yes, absolutely. Maslow wasn’t the first psychologist to develop a theory of human needs. Walter Langer presented a theory with physical, social and egoistic needs that appeared alongside Maslow’s in an early management textbook. And Maslow’s theory generally hasn’t performed well in empirical studies (although I’m aware of your recent research which challenges this).
In fact, this lack of empirical support is one of the main criticisms of the theory made by textbook authors. So why do they continue to include it? The pyramid. We know from having taught management courses for 20 years that if there’s one thing that students remember from an introductory course in management, it’s the pyramid. It’s intuitively appealing, easy to remember and looks great in PowerPoint. Students love it and because of that, so do textbooks authors, teachers, and publishers.
Question: So what’s your problem with the pyramid?
It’s described as ‘Maslow’s pyramid’ when he did not create it and it’s just not a good representation of Maslow’s hierarchy of needs. It perpetuates unfair criticisms of the theory. For example, that people are only motivated to satisfy one need at a time, that a need must be 100% satisfied before a higher-level need kicks in, and that a satisfied need no longer affects behavior.
Another is the view that everyone has the same needs arranged and activated in the same order. In his 1943 article in Psychological Review Maslow anticipates these criticisms and says they would give a false impression of his theory. Maslow believed that people have partially satisfied needs and partially unsatisfied needs at the same time, that a lower level need may be only partially met before a higher-level need emerges, and that the order in which needs emerge is not fixed.
Question: How did this inaccurate interpretation of the hierarchy of needs become established in management textbooks?
It’s a complicated story and one we address fully in the paper. Douglas McGregor is a key figure, because he popularized Maslow within the business community. McGregor saw the potential for the hierarchy of needs to be applied by managers, but for ease of translation he deliberately ignored many of the nuances and qualifications that Maslow had articulated. To cut a long story short, McGregor’s simplified version is the theory that appears in management textbooks today, and most criticisms of Maslow’s theory are critiques of McGregor’s interpretation of Maslow.
Question: Did McGregor create the pyramid? Or if not, who did?
No pyramid appears in McGregor’s writing. Keith Davis wrote a widely-used management textbook in 1957 that illustrated the theory in the form of a series of steps in a right-angled triangle leading to a peak. The top level shows a suited executive raising a flag, reminiscent of the flag-raising at Iwo Jima. But this representation of the theory did not catch on.
We traced the pyramid that we associate with the hierarchy of needs today to Charles McDermid, a consulting psychologist. It appeared in his 1960 article in Business Horizons ‘How money motivates men’ in which he argued the pyramid can be applied to generate “maximum motivation at the lowest cost”. We think McDermid’s pyramid was inspired by Davis’ representation, but it was McDermid’s image that took off. If there is an earlier pyramid, we did not find it.
Question: Is it right that you actually found no trace of Maslow framing his ideas in pyramid form? Where did you look, and how comprehensive was your search?
That’s correct. It was a comprehensive search. Maslow was a prolific writer. We examined all of his published books and articles that we could identify, as well as his personal diaries, which are published. John immersed himself in the Maslow archives at the Centre for the History of Psychology at the University of Akron in Ohio and examined many boxes of papers, letters, memos, and so forth. We found no trace of the pyramid in any of Maslow’s writings. Additionally, John went through pre1960 psychology textbooks for any discussions of Maslow. Most psych books in those times did not even mention Maslow.
Question: Why didn’t Maslow argue against the Pyramid once he saw it? He could have criticized it, right? I heard from someone who knew Maslow that he actually thought the pyramid on the back of the $1 bill was a fair representation of his theory.
Also, one of his students who took his course at Brooklyn College told me he would include a slide of the pyramid when he described his theory in class. So perhaps he was pleased with the iconic pyramid even if he didn’t invent the depiction himself?
Answer: Those are interesting questions. Maslow lived for 10 years after McDermid presented the pyramid. We found no evidence of Maslow challenging the pyramid at any time. We don’t think that’s because he regarded pyramid as an accurate representation. A more plausible explanation, which comes from our analysis of his personal diaries, is that aspects of his professional life were unravelling.
He felt underappreciated in psychology. The major research journals in psychology had been taken over by experimental studies, which depressed Maslow for their lack of creativity and insight. He also had more pragmatic concerns, suffering periods of ill health and financial difficulties. Key figures in the management community saw him as a guru and rolled out the red carpet. They gave him the recognition he felt he deserved. Furthermore, through speaking engagements and consulting, he could generate additional income. Seen in that light, it’s not surprising he went along with it.
Question: You wrote: “Inspiring the study of management and its relationship to creativity and the pursuit of the common good would be a much more empowering legacy to Maslow than a simplistic, 5-step, one-way pyramid.” I agree! It seems like Maslow’s original thinking about self-actualization is at odds with how business leaders treated the concept, right?
Definitely. Following the publication of Motivation and Personality in 1954, Maslow emerged as one of the few established psychologists to challenge the prevailing conformism of the 1950s. He spoke out on how large organizations and social conformity stifled individual self-expression. At times he was frustrated that the business community treated his theory of human nature as a means to a financial end–short-term profits–rather than the end which he saw, a more enlightened citizenry and society.
It would be great if students were encouraged to read what Maslow in the original. Students would better understand that motivating employees to be more productive at work was not the end that Maslow desired for the hierarchy of needs. He was concerned with creativity, freedom of expression, personal growth and fulfillment – issues that remain as relevant today in thinking about work, organizations, and our lives as they were in Maslow’s time. We think there’s an opportunity to create a new Maslow for management studies by returning to Maslow’s original ideas.
State of the theory today
William Kremer and Claudia Hammond write
There is a further problem with Maslow’s work. Margie Lachman, a psychologist who works in the same office as Maslow at his old university, Brandeis in Massachusetts, admits that her predecessor offered no empirical evidence for his theory. “He wanted to have the grand theory, the grand ideas – and he wanted someone else to put it to the hardcore scientific test,” she says. “It never quite materialised.”
However, after Maslow’s death in 1970, researchers did undertake a more detailed investigation, with attitude-based surveys and field studies testing out the Hierarchy of Needs.
“When you analyse them, the five needs just don’t drop out,” says Hodgkinson. “The actual structure of motivation doesn’t fit the theory. And that led to a lot of discussion and debate, and new theories evolved as a consequence.”
In 1972, Clayton Alderfer whittled Maslow’s five groups of needs down to three, labelled Existence, Relatedness and Growth. Although elements of a hierarchy remain, “ERG theory” held that human beings need to be satisfied in all three areas – if that’s not possible then their energies are redoubled in a lower category. So for example, if it is impossible to get a promotion, an employee might talk more to colleagues and get more out of the social side of work.
More sophisticated theories followed. Maslow’s triangle was chopped up, flipped on its head and pulled apart into flow diagrams. Hodgkinson says that one business textbook has just been published which doesn’t mention Maslow, and there is a campaign afoot to have him removed from the next editions of others.
The absence of solid evidence has tarnished Maslow’s status within psychology too. But as a result, Lachman says, people miss seeing that he was responsible for a major shift of focus within the discipline.
“He really was ground-breaking in his thinking,” Lachman says. “He was saying that you weren’t acting on the basis of these uncontrollable, unconscious desires. Your behaviour was not just influenced by external rewards and reinforcement, but there were these internal needs and motivations.”
Abraham Maslow and the pyramid that beguiled business, William Kremer and Claudia Hammond, BBC World Service 9/1/2013
American Surplus and Supplies (Sciplus)
Daydream Education (great science posters)
Delta Education (K-8)
Educational Innovations (Teachersource)
Frey Scientific & CPO Science
NASCO (STEM, STEAM products)
STEMfinity (technology, engineering, robotics)
ThermoFisher Scientific (Massachusetts)
Trend Enterprises posters
Wards’s Science / SK Science Kit & Boreal Laboratories
Easy labs and manipulatives
Creating the periodic table
Exploratorium Science Snacks
(San Francisco, California)
Animals don’t make their own food – they have to find food and eat it. Plants, however, are totally different. They actually make their own food!
Organisms that make their own food are called autotrophs or producers. (they mean the same thing.)
Of course, they do need some things to build this food from. They need carbon dioxide gas (CO2) water (H2O), a few trace minerals, and energy.
Let’s follow the diagram: What is going in to this leaf? What is coming out of it?
And what exactly is a carbohydrate? Just a bunch of sugar molecules connected together into a bigger structure. Let’s see how this works.
This is a sugar molecule. C6H12O6. That means there are 6 Carbon atoms, 12 Hydrogen atoms, and 6 oxygen atoms.
Plant cells stitch many of these sugars together into bigger structures. They can be called polysaccharides or carbohydrates.
What are they used for? The plants use them as building blocks. You can see “hemicellulose,” basically a carb, being linked together with other interesting looks carbs. They keep linking until they build the structure of a leaf, a stem, or as you can see here, a branch.
Let’s follow the next diagram: Energy enters from sunlight.
We see an organelle with little green stacks absorbing the sunlight. That’s the chloroplast. What comes out of it?
We see organic molecules – sugars! – come out of the chloroplast. Also O2 (oxygen gas) comes out of it.
Where do they go? They enter another organelle, the mitochondria – the powerhouse of the cell!
This produces ATP, a chemical that stores energy. Everything else in the cell that uses energy? That would use these ATP molecules.
Here’s an animation of how this works, as a formula:
Here you can use an interactive app to control photosynthesis!
And just because you know that you wanted to see this, here you actually see chloroplasts in plant cells!
In this kinesthetic model, students will learn that plants need carbon dioxide, water, and sunlight to carry out photosynthesis.
Using ping pong balls and egg cartons, they will simulate the production of sugar molecules to store energy (photosynthesis), and then break apart these molecules to acquire energy (cellular respiration).
This active simulation makes it easier to remember both processes!
How do viruses spread?
Not by individual virus particles
An individual virus particle is unbelievably tiny.
Since they are so lightweight they can float in the air for relatively long distances. So that makes them airborne, right?
Yet these airborne individual virus particles are almost never a problem. Studies show that people are not at risk of being infected by single viral particle.
Why not? We’re likely always inhaling single viral particles here and there. But they quickly break down, or if they persist then our immune system quickly wipes them out.
So if that ain’t the problem then what is? The problem is when we encounter a drop of fluid, or a solid surface, which may have many hundreds or thousands of such viral particles.
Try not to touch people who may be infected! If you do touch someone then wash your hands first.
When it comes to this novel coronavirus (its formal name is SARS-CoV-2) we have to be very careful: An infected person can leave viral particles behind on anything they touch or breathe on.
Infectious material could be left behind on a table, supermarket cart, keypad on an ATM machine, a computer keyboard, on a phone, etc.
A healthy person might touch one of those surfaces, and then touch their face, which then lets those virus particles get in to your airway. That’s a problem, but we can avoid danger: Be careful of what you touch and wash your hands!
Viruses spread exponentially
How does the likelihood of death from any common cause compare to the likelihood of death from something that spreads exponentially? The important difference is that for any other cause of death, that cause is (a) usually not transmissible, and (b) the rate of death stays (more or less) the same over time.
But for deaths caused by a virus the situation is different – (c) it is transmissible from one person to another, and (d) the number of people infected grows exponentially over time.
Droplets from sneezing and coughing
Sneezing or coughing sends out lots of tiny, snotty water droplets. Each droplet could hold thousands of viral particles. If we inhaled some of these drops then that is enough to make us sick.
Most droplets are short range. The larger ones only go about six feet before they fall to the ground. That’s why it is important to practice social distancing. Stay at least six feet away from people outside of your home.
But read on – with this novel coronavirus (SARS-CoV-2) there is a bit more danger:
Smaller droplets remain in the air longer
The big particles fall quickly, but the small particles float in the air longer – and then they dehydrate (they lose water molecules.) That leaves an even tinier, lighter particle.
These super tiny particles are almost like a gel. Some call these droplet nuclei, or an aerosol, or a bioaerosol. The danger is that these very tiny globs remain airborne much longer, and can travel a further distance. They can float over 20 feet!
That isn’t quite far enough for a virus to technically be called “airborne,” but it still is super dangerous. So if you are indoors – like in a supermarket – the air could become saturated with lots of these tiny droplet nuclei, making the location unsafe.
So when people were saying “this is new coronavirus is bad, but at least it isn’t airborne,” we now know that they were partially incorrect. When indoors this virus is somewhat airborne (6 to 20 feet), and that’s why one needs to avoid supermarkets unless necessary.
Health authorities suggest wearing a mask if you have to do so. Even an imperfect mask is better than none at all.
Truly airborne viruses
An airborne virus is one that can float in very tiny aerosol drops, less than 5 microns across, for hours and still remain infectious.
A micron is 0.001 millimeters , or 0.000039 inch.
Its symbol is μm
We now have evidence that this novel coronavirus, SARS-CoV-2, is an airborne virus.
The National Academy of Sciences (NAS) has given a boost to an unsettling idea: that the novel coronavirus can spread through the air—not just through the large droplets emitted in a cough or sneeze. Though current studies aren’t conclusive, “the results of available studies are consistent with aerosolization of virus from normal breathing,”
researchers reported earlier this year in The New England Journal of Medicine that SARS-CoV-2 can float in aerosol droplets—less than 5 microns across—for up to 3 hours, and remain infectious
You may be able to spread coronavirus just by breathing, new report finds, Science, AAAS, Robert F. Service, 4/2/2020
Yes, wearing cloth face masks works!
Cloth masks can help stop the spread of COVID-19, save lives and restore jobs. About 95% of the world lives in countries where the government and leading disease experts both agree that masks are effective at reducing the spread of COVID-19.
Anyone not wearing a cloth mask in public puts everyone at risk of getting infected and they hurt our economy by increasing the chances of a second lockdown.
Why? The U.S. CDC and most experts agree that many infected and contagious people don’t know they’re sick because they don’t have symptoms. Wearing a mask significantly reduces the chances of spreading COVID-19 from you to others.
“Some people have said that covering their faces infringes on their rights, but…it’s about protecting your neighbors…Spreading this disease infringes on your neighbors’ rights.” –Larry Hogan, Governor of Maryland (Republican)
“If everybody’s wearing a mask, it will dramatically reduce the opportunity and possibility of spread.” –Charlie Baker, Governor of Massachusetts (Republican)
Countries that have contained major COVID-19 outbreaks have close to 100% mask usage. An international review of the scientific research on masks by 19 experts (from Stanford, MIT, Oxford, UPenn, Brown, UNC, UCLA, and USF) concluded that:
Near-universal adoption of non-medical masks in public (in conjunction with other measures like test & trace) can reduce effective-R below 1.0 and stop the community spread of the virus.
Laws appear to be highly effective at increasing compliance and slowing or stopping the spread of COVID-19.
There are “34 scientific papers indicating basic masks can be effective in reducing virus transmission in public — and not a single paper that shows clear evidence that they cannot.” –The Washington Post
Flight of the aerosol, Ian M Mackay et al. Virology Down Under, 2/9/2020