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Estimates of the mass of the Milky Way vary, depending upon the method and data used. At the low end of the estimate range, the mass of the Milky Way is × 10 11   solar masses ( M ☉ ), somewhat less than that of the Andromeda Galaxy . [48] [49] [50] Measurements using the Very Long Baseline Array in 2009 found velocities as large as 254 km/s (570,000 mph) for stars at the outer edge of the Milky Way. [51] Because the orbital velocity depends on the total mass inside the orbital radius, this suggests that the Milky Way is more massive, roughly equaling the mass of Andromeda Galaxy at 7 × 10 11   M ☉ within 160,000 ly (49 kpc) of its center. [52] In 2010, a measurement of the radial velocity of halo stars found that the mass enclosed within 80 kilo parsecs is 7 × 10 11   M ☉ . [53] According to a study published in 2014, the mass of the entire Milky Way is estimated to be × 10 11   M ☉ , [54] which is about half the mass of the Andromeda Galaxy. [54]


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DANGEROUS MAGLEV!   RECURRING SCIENCE MISCONCEPTIONS IN K-6 TEXTBOOKS
William J. Beaty 3/1995
WARNING: This file is currently being written, edited, corrected, etc. It does still contain some mistakes of its own. I placed it online as a sort of 'trial by fire' in order to hear readers' responses so I could target weak or unclear sections for improvement. (And, as my site points out, NOBODY is perfect so we should always practice critical thinking. Take all information with a grain of salt, including everything here!) Please feel free to send public comments to me with the COMMENT BOOK . If you prefer that nobody else sees your comments, send private comments to me via this form.

Videos:
         
          What color is water?
See also another misconceptions list by Dr. J. L. Hubiz " Lest you think that I am quibbling over minor points of language, I note that in my experience many of the misconceptions people harbor have their origins in imprecise language... Precise language is needed in science, not to please pedants but to avoid absorbing nonsense that will take years, if ever, to purge from our minds. " - Dr. Craig F. Bohren, Physicist THE MISCONCEPTIONS: also: Electricity Misconceptions      Static Electric Misconceptions "Errors, like straws, upon the surface flow; He who would search for pearls must dive below." - John Dryden also: Electricity Misconceptions      Static Electric Misconceptions That's the way all the books were: They said things that were useless, mixed-up, ambiguous, confusing, and partially incorrect. How anybody can learn science from these books, I don't know, because it's not science. - RP Feynman , in Judging Books By Their Covers Want books? Try searching :
(try "science projects" too)   CORRECT: There is no single list called "The Scientific Method." It is a myth.
See the links and references below.
The rules of a science-fair typically require that students follow THE SCIENTIFIC METHOD, or in other words, hypothesis-experiment-conclusion. The students must propose a hypothesis and test it by experiment. This supposedly is the "Scientific Method" used by all scientists. Supposedly, if you don't follow the rigidly defined "Scientific Method" listed in K-6 textbooks, then you're not doing science. (Some science fairs even ban astronomy and paleontology projects. After all, where's the "experiment" in these?)
Unfortunately this is wrong, and there is no single "Scientific Method" as such. Scientists don't follow a rigid procedure-list called "The Scientific Method" in their daily work. The procedure-list is a myth spread by K-6 texts. It is an extremely widespread myth, and even some scientists have been taken in by it, but this doesn't make it any more real. "The Scientific Method" is part of school and school books, and is not how science in general is done. Real scientists use a large variety of methods (perhaps call them methods of science rather than "The Scientific Method.") Hypothesis / experiment / conclusion is one of these, and it's very important in experimental science such as physics and chemistry, but it's certainly not the only method. It would be a mistake to elevate it above all others. We shouldn't force children to memorize any such procedure list. And we shouldn't use it to exclude certain types of projects from science fairs! If "The Scientific Method" listed in a grade school textbook proves that Astronomy is not a science, then it's the textbook which is wrong, not Astronomy.
"Ask a scientist what he conceives the scientific method to be and he adopts an expression that is at once solemn and shifty-eyed: solemn, because he feels he ought to declare an opinion; shifty-eyed because he is wondering how to conceal the fact that he has no opinion to declare." - Sir Peter Medawar There are many parts of science that cannot easily be forced into the mold of "hypothesis-experiment-conclusion." Astronomy is not an experimental science, and Paleontologists don't perform Paleontology experiments... so is it not proper Science if you study stars or classify extinct creatures?
Or, if a scientist has a good idea for designing a brand new kind of measurement instrument (. Newton and the reflecting telescope) ...that's certainly "doing science." Humphrey Davy says "Nothing tends so much to the advancement of knowledge as the application of a new instrument." But where is 'The Hypothesis?' Where is 'The Experiment?' The Atomic Force Microscope (STM/AFM) revolutionized science. Yet if a mere science student had actually invented the very first reflector telescope or the very first AFM, wouldn't such a device be rejected from many school science fairs? After all, it's not an experiment, and the list named "The Scientific Method" says nothing about exploratory observation. Some science teachers would reject the discovery of the Tunneling Microscope as science; calling it 'mere engineering.' Yet like the Newtonian reflector, the tunneling microscope is a revolution that opened up an entire new branch of science. Since it's instrument-inventing, not hypothesis-testing, must we exclude it as science? Were the creators of the STM not doing science when they came up with that device? In defining Science, the Nobel Prize committee disagrees with the science teachers and science fair judges. The researchers who created the STM won the 1986 Nobel Prize in physics. I'd say that if someone wins a Nobel Prize in the sciences, it's a good bet that their work qualifies as "science."
Forcing kids to follow a caricature of scientific research distorts science, misleads generations of students, and it really isn't necessary in the first place.
Another example: great discoveries often come about when scientists notice anomalies. They see something inexplicable during past research, and that triggers some new research. Or sometimes they notice something weird out in Nature; something not covered by modern theory. Isaac Asimov said it well: "The most exciting phrase to hear in science, the one that heralds new discoveries, is not 'Eureka!' (I found it!) but 'That's funny...' " This suggests that lots of important science comes NOT from proposing hypotheses or even from performing experiments, but instead comes from unguided observation and curiosity-driven exploration: from sniffing about while learning to see what nobody else can see. Scientific discovery comes from something resembling "informed messing around," or unguided play. Yet the "Scientific Method" listed in textbooks says nothing about this. Instead their lists start out with "Form an Hypothesis." As a result, educators treat science as UNplayful, deadly serious business. "Messing around" is sometimes dealt with harshly. See: The Onion, science teacher satire . "Let me state the Method Position as follows: 'There is something called the scientific method, and someone who understands this method will be able to understand all of science, regardless of the specific subject matter that person has been taught. Thus the goal of science education should be to teach that method.'          It's hard for me to understand how anyone could hold a position that is so clearly untenable. " - Dr. James Trefil,
  "Two Modest Proposals Concerning Scientific Literacy." SOME BOOKS ARTICLES: " Why should there be the method of science? There is not just one way to build a house, or even to grow tomatoes. We should not expect something as motley as the growth of knowledge to be strapped to one methodology. " -Ian Hacking
CORRECT: The ocean is blue because water is a blue substance.
Many people are sure that bodies of water are blue because the water reflects the sky. But wouldn't this only make the shiny surface-reflections look blue? And doesn't water sometimes remain blue on cloudy days ? Exactly. There's no mystery here; water looks blue because water *is* blue. Pure water is a blue chemical. It's not just the sky that creates the colors we see.
What color is water?
(Wbeaty youtube 1:08) But what if you pour yourself a drink; in that case the water is clear, right? Well ...it's not blue as far as your eyes can tell. But what if the water in your cup actually was very very slightly blue. You'd never see it. You'd only notice the blue color if your cup was many feet wide.
In fact, that's exactly how it works: pure water is nearly clear, but it's very very slightly blue. A small amount of water is too thin a layer, so a small amount looks clear rather than blue. But look through thirty feet of water, especially with a white sandy bottom, and you'll see a strong color. Gaze into a hundred feet of deep pure mountain lake water against a white rocky bottom on a sunny day. You'll see exactly what color the water actually has. Yet if you scoop a canteen full of that lake water, it will seem totally clear.
See:
- "Why is water blue?" J. Chem. Edu., 1993,70(8), 612
- Causes of Color ( )
- London South Bank U.: Water absorption spectrum
- Wikipedia: Color of Water
To see some obvious blue, go to the Bahamas and compare the difference between the white sand beaches, the underwater sand in shallow water, and the sand in deeper water: Or watch a video of a light-colored swimming pool turning blue CORRECT: The sky is blue because air is blue.
This one isn't purely a textbook error. Still, it involves misconceptions on the part of authors.
Why is the sky colored blue? Usually the books start going on about wavelengths of light, Tyndall effect, and Rayleigh scattering. It's a bit much for young children. First the books try to teach some correct but complicated physics. Then they use it to explain blue sky and sunsets. But what happens when kids don't understand the physics? Is our explanation useless? And do the kids just give up?
It's all wrong: we don't need complicated physics to understand this. The sky is blue for a very simple reason: The Earth's atmosphere is not a perfectly transparent material. Instead it's blue! There is no "The Sky." The only material up there is air. Take away the air, and then we'd see what the lunar astronauts see: black daytime sky. No air? No blue. There's no "The Sky" up there; no solid surface. All we're seeing is sunlit air.
A big cloud of air looks blue for much the same reason that a cloud of powder looks white. Powder isn't invisible . Neither is air. Throw some dust upwards on a sunny day and you'll see a visible white cloud. But what happens if you could throw some AIR? You might think that a cloud of air would be invisible. You'd be wrong. Air isn't invisible, instead its molecules scatter light in the same way that any small particles do. Deposit a huge cloud of air onto the surface of the airless moon, and you'd see its bright blue color against the blackness of hard vacuum. Air is a powdery-blue substance. (But then... shouldn't air be a white substance? Yes! And that's where the complicated physics comes in. Once we know that the sky is just a layer of air, and that sunlit air is bright blue, then we can use Rayleigh Scattering to explain why air looks blue rather than white.)
The color of air can be confusing because air seems transparent. Capture a jar full of air, but you see no color. Small amounts of air are almost perfectly transparent. But so are small amounts of water. Go to an opaque muddy river or pond and use a cup to dip out some water. The water in your cup looks fairly clear, no? Yet the deep river is opaque brown. Whenever you try to look through ten cups of water, or a hundred cups, the water seems to turn into opaque brown paint. Yet a single cup of river water ...it almost looks clean! (Aheh, don't drink any.)
Air behaves like water. A mile of air looks clear, but ten miles of air looks misty blue, and a thousand miles of air looks opaque white. The air is acting like the dirty river water where a thin layer looks colorless but a thick layer does not. Air acts like a fogbank where distant objects are invisible, yet you can see your own hand just fine.
"The sky" is blue because air is a powdery blue material; a collection of tiny specks, and when the sun shines upon it, we can see this blue color. Each molecule of air behaves like mote of dust. Stare upwards on a sunny day, and you're looking into a thick cloud of brightly-lit air. (Note: there really is no "sky" up there at all. The sky is an illusory surface. You're not really looking at a blue surface. There is no "sky" which is colored blue, instead you're just seeing the Earth's layer of blue air against the blackness of outer space. )
OK, suppose you could go far out into space away from the Earth, then build yourself a thin hollow glass bubble a thousand miles wide. Viewed from the Earth, your empty glass bubble would be almost invisible. OK, now fill your bubble with air. It won't be invisible any more. It will look like a giant droplet of bright blue paint. It probably even looks whitish in the middle, since very thick layers of air seem as white as milk. What if you let your giant glass bubble crash into the moon? The air inside would pour out over the moon's surface and form a thick temporary layer of atmosphere. The moon wouldn't look white anymore. It would have the same blue borders that Earth has.
Photos of sunlit air, observed against black space: OK, now here's a question. Smoke is white, milk is white, and powder is white. A big cloud of particles should look like white smoke, not like blue dye. Why is air blue? Shouldn't it look white? And even more important, why are sunsets red? (Does this mean that air is also a red substance?!! I'd have to say yes!) Air is colored reddish for transmitted light, but its color is bluish for reflected light. The color of air is not fixed, instead it's like opal jewelry: the color changes with viewing angle.
Ah, if you start asking why air acts like this, *now* you finally need the advanced physics explanations. Many physics books will explain Rayleigh scattering; explain why an air molecule looks like a bluish dust mote, but looks reddish when lit from behind. CORRECT: Clouds actually remain aloft because they are warm inside.
Clouds are heavy. Evaporated water (the H2O gas) is not heavy, it actually is less dense than air, so moist air rises. But when the water-gas condenses to form clouds, it contracts by about 1000 times and turns into very dense liquid water. (Imagine that the helium in a balloon condensed into a liquid. Would a tiny liquid-filled balloon still be buoyant? Nope.)
Even a small cloud contains many tons of liquid water. How can clouds remain aloft?
Many sources claim that clouds remain aloft because the water droplets are so small and widely separated that gravity has less effect on them. This is wrong. It doesn't matter if you break up a body of water into tiny droplets; its weight remains the same. You can't fool gravity. If a cloud contains tons of water, it will be pulled down to the Earth's surface with the same force whether the water forms a cloud or whether it forms raindrops. The answer lies elsewhere.
Some sources claim that clouds remain aloft because of updrafts: because the air had been rising, and the rising air blows the cloud droplets upwards. Wrong again: An updraft should be quickly halted as soon as the low-density water vapor turns into a dense liquid. The excess weight will slow the updraft, stop it, then reverse it. To keep clouds aloft, we'd need some sort of weirdly constant updraft, or one where thermal energy is being created, not an updraft that's easily reversed by a falling cloud.
Still other sources claim that clouds stay up there because the droplets are very tiny, so they settle through the air very slowly. This is true, but it still doesn't explain how weighty water can remain aloft. Stop and think a bit... if we have hundreds of tons of water, will its weight disappear simply because it has been divided into tiny droplets? No, instead the heavy droplets drag the surrounding air downwards as they fall. Air which contains water droplets is denser than normal air. Its weight is increased by almost exactly the weight of the suspended water droplets, which works out to around 1/10 percent of the weight of the air in a particular volume.) Dense air falls fast! In other words, the tiny droplets will still race downwards because they form heavy white cloud-stuff, and both the droplets and the air between them will be dragged downwards by gravity. Anyone playing with humidifier fog knows this: dense white pours downwards like a liquid. Yet even some professional meteorologists are saying these things about droplets. They should know better.
So why *DO* clouds stay up there? Why don't they pour downwards to form a ground-hugging fog? The answer is simple: the weight of the cloud's droplets is countered by the buoyancy of heated air between the droplets. Clouds are like hot air balloons!
Whenever liquid water condenses from H2O gas, it releases thermal energy. When moist air turns into droplet-filled air, the droplets are hot, and they warm the air too. The heated air expands and becomes less dense. Is this enough to stop the falling droplets? Yes, it's more than enough, and the warm foggy air flows upwards. Clouds stay up there because they're significantly less dense on average than the surrounding air. In fact, if the water droplets should meld together, then fall out of the cloud as rain, then the remaining hot air is no longer weighed down by tons and tons of water, and it rises even more quickly. This low-density, upward moving warm air is the "engine" which drives the violent updrafts in thunderstorms and hurricanes. Hot air with its water removed no longer floats serenely along as clouds, instead it can form upward jets with hurricane velocity.
Try making this "Touch The Clouds" device and you'll discover that droplet-filled air can be very dense indeed. You can easily pour it from a pitcher and fill some cups. But we also know that hot air is less dense that cool air of the same pressure, so hot must rise through cooler air. Mix the two ideas together: dense air which is full of water droplets becomes less dense when heated, and at a certain higher temperature it should be buoyed upwards by the atmosphere even though it's still full of suspended mass-bearing water droplets. If we could make the humidifier-mist warm enough, it would rise and form indoor ceiling-clouds.
More thinking: helium gas rises in air, but liquid helium does not. Liquid helium is heavy, like liquid water (though not quite as heavy as an equal quantity of water.)
So, what happens when helium gas condenses into liquid? It shrinks greatly, becoming more dense than the surrounding air, then it dribbles downwards like any liquid. It falls downwards if it's a large blob of liquid, and it falls downward even if it takes the form of tiny droplets. If the helium in a balloon was changed into liquid, the balloon would fall. The same is true of water. Water vapor (h2o gas,) like helium, is lighter than air, and it will rise. However, if that vapor should condense into droplets, it greatly contracts in size and greatly increases in density. A cloud of water droplets is heavy, and on average it should fall downwards. Even if the droplets are so tiny that they individually settle slowly, the droplets together have significant weight, so the droplets should drag the air downwards as they go. The dense, droplet-filled air may fall quite quickly, even though the individual droplets remain "stuck in the air" because of forces of viscosity.
Whenever vapor condenses to form droplets, it releases "heat of condensation" which causes the remaining air to expand. The warm air can expand even MORE than the volume left empty by the condensing vapor, causing the average density to fall and causing clouds to rise upwards rather than just float. When clouds first form, they usually pour upwards, not downwards. They're a bit too warm, so they try to rise to a higher level.
  • Wrong: Scientific American "Ask an Expert" Tell them to calculate the heat released by condensation of cloud water, the temperature of resulting air, and the weight of a 1KM cloud compared to 1KM of nearby air which is cooler yet droplet-free.
  • Wrong: New Scientist "Last Word"
  • Wrong: National Geographic Kids
  • Wrong: UK ScienceLine
  • Wrong: Star Tribune: kid's weather questions
  • Wrong: Madsci: ask an expert
  • Wrong: U. Indiana Moment in Science
  • Wrong: U. Corp. Atmos Research
  • Wrong: NASA . (they even mention "lighter than air"... then deny it!
  • Wrong:
  • Wrong: Starbase outreach pgm
    Correct:
  • Steve's Weather FAQ
  • n

    CORRECTED: A single lemon battery cannot light a flashlight bulb
    Some gradeschool science books contain "experiments" which do not work. The prism experiment below is one of them. Another is the "lemon battery" or "potato battery" used to run a flashlight bulb. If you stick some copper and zinc into a single lemon, this "battery" does create a small voltage. Touch your lemon-cell to the wires of a loudspeaker or headphones and you'll hear a clicking sound. Connect it to an old-style panel meter (a voltmeter or milliamp-meter; the kind with the moving needle,) and your lemon can make the meter needle move. Three or four lemon-cells connected in series can run an LCD digital clock or light up a red Light Emitting Diode LED. (If you try the digital clock or LED, remember that polarity is important, and if it doesn't work, try reversing the connections.)
    HOWEVER... the lemon's electrical output is far too feeble to light up a standard flashlight bulb. Same with motors, buzzers, etc. The lemon battery is too weak. The experiment described in the books doesn't work.
    How can I be certain? All those books say one thing, and I'm just one person who says differently. Doesn't the majority rule? No, because science is based on reality staying the same, and Nature ignores what humans vote upon. It doesn't matter how many books say that lemon batteries can light a flashlight bulb. Nature can't be fooled.
    Let's look at a real world example: I stick a fairly wide copper strip and a similar zinc strip into a lemon. (This works much better than copper pennies or zinc nails.) Clean the strips with sandpaper beforehand. First use the strips to tear up the inside of the lemon, then insert the metal strips very close together to give best results. The area of each "battery plate" is around 1 inch square. Measured voltage: . Measured short-circuit current: two milliamps ( Amps) immediately decreasing to a constant half a milliamp ( amps.) What does this mean? Well, a typical flashlight bulb draws an ENTIRE QUARTER OF AN AMPERE when lit. Not a half-milliamp, but 250 milliamps or Amps. To light up a normal flashlight bulb, you'd need 500 lemons wired in parallel! / = 500 lemons.
    However, there are specialized light bulbs which draw very tiny currents. Maybe the experiments in the books weren't talking about a standard flashlight bulb? (Most of them never say. But I'll give them the benefit of the doubt, although perhaps I shouldn't.) From Radio Shack we can get a #272-1139 incandescent bulb which only draws around fifteen milliamps ( amps) at volts when lit very dimly in a darkened room. This is the most sensitive incandescent bulb I've ever encountered. To light this bulb we only need / = 30 lemons wired in parallel. THIRTY LEMONS. And the bulb is so dim that you can't see the glow unless the room is dark. But wasn't the lemon's electric current higher at the start? amps, not amps? Yes, so with only TEN LEMONS wired in parallel, maybe we could cause the special hyper-sensitive light bulb to blink on for a second or two before going dark.
    This still translates into " the experiment doesn't work ." One single lemon cannot light up any sort of incandescent bulb. At best we can use several lemons to light an LED.
    If a science book contains the lemon battery bulb-lightning experiment, it means that the author never performed the experiment to see if it works. LOTS of books and websites say that a single lemon can light a flashlight bulb. Every single one of these is wrong. The mistake is like a kind of infection. If you aren't careful, then your science website can catch a disease!
    Can't we build a larger lemon-juice battery in a jar which will light a small bulb? Yes, but your battery needs to be fairly large; much larger than a couple of metal parts stuck into a lemon. At the very least you'll need a jar for the juice, plus some sheets of copper and zinc several inches wide. If you don't have that special Radio Shack bulb, then you'll need more than one lemon-juice jar hooked in series to make the volts needed by a standard flashlight bulb. (I'll try building one of these and report back about how large the copper and zinc plates must be.)
    If you really want to light up a small lightbulb, why not build an ELECTRIC GENERATOR instead?
    How to cheat! There is a secret way to make a lemon-cell light up an incandescent bulb. You have to cheat. Buy yourself a "super capacitor" or "memory backup capacitor" via mail-order surplus. They cost a few dollars. You want a value between farad and farads. Try one of these suppliers:
    • All Electronics
    • Electronics Goldmine
    • Jameco Electronics
    To light a bulb, first build a lemon battery and connect it to the terminals of the supercapacitor. (Me, I use alligator clip-leads bought from Radio Shack.) Wait for a few minutes. Now connect your flashlight bulb to the supercapacitor terminals and it should light brightly for a few seconds. (If not, then remove the bulb and try connecting your lemon cell to the capacitor for 15 minutes to make sure the capacitor gathers enough energy.) The capacitor slowly collects electrical energy from the lemon battery, then it dumps that energy into the flashlight bulb over a very short time. You can even use this trick to let your lemon battery run a low-voltage buzzer or turn a small motor (look for "solar cell motors" from various mail order suppliers or Radio Shack.) As with the bulb, you must charge up the capacitor for many minutes, then use it to run your bulb or motor for a few seconds.
    It's not an ideal experiment, and it's hard to explain how capacitors work. But it's easier than trying to connect thirty lemon-cells in parallel!
    • Four lemons light an LED
    • Note about Lemon energy
    • Tongue tingle, but no lightbulb
    • Digital watch yes, lightbulb no
    • Google search for websites with the bad lemon experiment
    • Google images : one lemon with one bulb
    CORRECTED: Ice skates do not function by melting ice via pressure
    It is commonly stated that ice skates have low friction because ice melts when pressure is applied to it. This is not quite correct. A demonstration using an ice cube, a wire, and two weights is often provided to illustrate the phenomena. However, while pressure does affect the melting point of ice, the pressure provided by the skates is not enough to melt ice except when the temperature is a fraction of a degree below 0C. Also, the icecube and wire demonstration is very misleading because it is always performed in a heated room, and the wire doesn't melt ice entirely by pressure, it melts the ice by thermal conduction of warm room temperature along the wire. (Also, narrow gaps in ice always freeze closed because the simultaneous melt/freeze process at water/ice boundary acts to flatten points and fill crevices) Another point: the weight of small objects is too low to create high pressure, yet small objects do experience low friction when on ice. The low friction of ice is probably caused by a layer of liquid water a few hundred molecules thick which always spontaneously develops on the surface of ice. Also, melting from frictional heating can provide liquid water as lubrication. Here's more on this whole debate, and also a bit from BAD CHEMISTRY
    CORRECTED: there are not 92 elements on Earth
    Uranium has the highest atomic number of the elements commonly found in the environment, and some books will tell you that there are 92 elements found on earth: atomic numbers 1 through 92 (hydrogen through uranium). This is wrong. Unfortunately there are two elements below Uranium which are radioactive and have extremely short half lives. These are Technetium and Promethium. These two elements do not occur naturally on Earth, and this reduces the total number of elements found in the environment to 90. However, in the 1970s a natural uranium reactor was found in an ancient streambed in Africa, and the mineral deposits at the site contained traces of a long-lived Plutonium isotope (atomic number 94.) This brings the total number of elements on the Earth back up to 91. (Note: Technetium, though not found naturally on Earth, is present in some stars, detected by spectral analysis.) See THE PHYSICS TEACHER, p282
    Light from the sun is parallel? Nope.
    Some books state that because the sun is so far away, sunlight arriving at the Earth is almost perfectly parallel. This is incorrect. The book authors reason that, the more distant the object, the more parallel the light, and since the sun is so far away, sunlight is perfectly parallel. They make a mistake. While it is true that light from *each tiny point* on the sun's surface is just about perfectly parallel by the time it reaches our eyes, light from the sun as a whole is not. This is because the sun, though very distant, is very large. A similar situation exists with light from the sky. We wouldn't say that the blue sky emits parallel light. Yet light from the sky comes from many miles away.
    Because the sun is a disk, it creates shadows with fuzzy edges called "penumbras." If sunlight were perfectly parallel, there would be some interesting effects which are usually covered up by these fuzzy edges. First of all, if sunlight was genuinely parallel, then to us the sun would look like a very bright point, like an intensely bright star or a welding arc. Also, shadows on the ground would lack penumbras and be almost perfectly sharp. Without the penumbras, diffraction of light waves would be revealed, and parallel dark and bright lines would appear at the edges of shadows. At nightfall the advancing shadows of distant mountains would be seen to race across the ground. During sunset the brilliant pointlike sun wouldn't gradually sink below the horizon, instead it would wink out. During the day the variations in air density would cause the ground to be covered by moving patterns of light; patterns similar to those seen on the bottom of a swimming pool but in this case made by "waves" in the sky. Solar and lunar eclipses would lack penumbrae. Looking at the sun might burn your retina, since the parallel light would be focused to a tiny point. And if sunlight were perfectly parallel, a large convex lens could concentrate sunlight into an intense pinpoint rather than into a small disk. Also, if a small concave lens were placed near the focus of a large convex lens, the pair lenses could be used to concentrate sunlight and form it into a thin, dangerously powerful parallel beam. Try doing this with the real sun, and all you get is a large, projected image of the sun's disk.

      CORRECTED: with an aircraft wing, the lifting force does not come from the difference in curvature between the top and bottom surfaces.
    First read the entire: wings/lift webpage
    Some books say that the lifting force appears because the wing's upper surface is longer than the lower surface. They state that air dividing at the leading edge of the wing must rejoin at the trailing edge, therefore the upper air stream must move faster, and so the wing is pulled upwards by the Bernoulli Effect. This is not correct: the air divided by the leading edge does NOT rejoin at the trailing edge, and there is no "race" to catch up.
    The same books often contain a misleading diagram showing a flat-bottomed wing with flow lines of the surrounding air. (see below.) This diagram actually shows a zero-lift condition. The lifting force is zero because the air behind the airfoil does not descend. In order to create lift in a three-dimensional situation, a wing must deflect air downwards .

    Both the explanation and the diagram have serious problems. They wrongly imply that inverted flight is impossible. They wrongly imply that an aircraft with a symmetrical wing (a wing with equal pathlengths above and below) will not fly. They also wrongly suggest that an aircraft can violate the conservation of momentum by remaining aloft without reacting against the air, and without causing a downward motion of the air.
    Yet upside-down flight is far from impossible; it is a common aerobatic move. And many wings have equal pathlengths, including even the thin cloth wings of the Wright Brothers' flyer! And anyone standing under a slow, low-flying plane, or below the thin, fast wings of a helicopter will know that there is a very great downward flow of air below the wings. All of this indicates that there is a serious problem with the "curved top, flat bottom" explanation. Below is an alternative.
    Go listen to NPR Science Friday Radio Archive , where physicist D. Anderson debunks the various lifting-force myths.
    Also see the NASA Aerodynamics Education site:
    • "Longer Path" myth is debunked
    • Simple Newton Explanation is debunked
    • "Half Venturi" myth is debunked
    • "Lift is partly Newton, partly Bernoulli" myth is debunked
    Here's my attempt at a correct explanation: As a plane flies, the leading edges of its wings have little effect on the air, while the trailing edges have a huge effect. The wings' trailing edges always move through the air at an angle. This "effective angle of attack" causes the wing to apply a downward force to the air. In order to create lift, the wing must be tilted. Or rather than being tilted, the wings can be curved or "cambered", which makes the trailing edge of the wing tilt downward at an angle. The trailing edges of the wings cause the departing air to move downwards at an angle. As a result, the wing is pushed upwards and backwards. (These two pushes are called "lift" and "induced drag.")
    The tilted lower surface of the wing causes air to move down, but that's not the only thing. The TOP of the wing also guides the flowing air. This is called "flow attachment" or "Coanda Effect." As the wing moves forward, the air ABOVE the wing moves down, and the wing is forced upwards. In other words, as any plane flies, its wings must send a stream of air diagonally downwards, and the wing acts like a 'reaction engine' just like a jet engine or a rocket. Unless a wing is either tilted or cambered, it cannot force the air downwards and cannot generate any "lift."
    It may help to imagine a hovering helicopter: a helicopter can hover because its rotor applies a downward force to the air, and the air applies an upward force to the rotor. As a result, the air flows downwards while the upward force supports the craft. But like any airplane, a helicopter rotor is a moving wing, and it's this small tilted wing which sends the air downwards. Like any wing, helicopter rotors are reaction engines, they push air downwards, and the air pushes them upwards. They are not "sucked upwards," and neither are airplanes.
    You may have seen a plane's downwash of air in movies: a "cropduster" plane sends out a trail of fertilizer mist, and the trail of mist does not float, instead it moves immediately down into the crops, driven downward by the moving air. Air from wings can even be dangerous: if a plane flies too low, the downwash from its wings can knock people over.
    The "Bernoulli effect" is still true. It explains how the top of the wing is able to "pull downwards" on the air flowing over it. And the Bernoulli Effect proves extremely useful in calculations of the lifting force during classes in airplane physics and during experimental work in aerodynamics. But airplanes also obey Newton's laws: accelerate some air downwards, and you'll experience an upwards force.
    • WEBSITE: Airfoil misconceptions in K-6 textbooks
    • SOME EMAIL DEBATE
    • My improved explanation: DISK BALLOONS
    Sound travels better through solids? No.
    Many elementary textbooks say that sound travels better through solids and liquids than through air, but they are incorrect. In fact, air, solids, and liquids are nearly transparent to sound waves. Some authors use an experiment to convince us differently: place a solid ruler so it touches both a ticking watch and your ear, and the sound becomes louder. Doesn't this prove that wood is better than air at conducting sound? Not really, because sound has an interesting property not usually mentioned in the books: waves of sound traveling inside a solid will bounce off the air outside the solid. The experiment with the ruler merely proves that a wooden rod can act as a sort of "tube," and it will guide sounds to your head which would otherwise spread in all directions in the air. A hollow pipe can also be used to guide the ticking sounds to your head, thus illustrating that air is a good conductor after all. Sound in a solid has difficulty getting past a crack in the solid, just as sound in the air has difficulty getting past a wall. Solids, liquids, and air are nearly equal as sound conductors.
    It's true that the speed of sound differs in each material, but this does not affect how well they conduct. "Faster" doesn't mean "better." It is true that their transparency is not exactly the same, but this only is important when sound travels a relatively great distance through each material. It's also true that complex combinations of materials conduct sound differently and may act as sound absorbers (examples: water with clouds of bubbles, mixtures of various solids, air filled with rain or snow.) And last: when you strike one object with another, the sound created inside the solid object is louder than the sound created in the surrounding air. So, before we try to prove that solids are better conductors, we had better make sure that we aren't accidentally putting louder sound into the solids in the first place.
    Gravity in space is zero? Wrong.
    Everyone knows that the gravity in outer space is zero. Everyone is wrong. Gravity in space is not zero, it can actually be fairly strong. Suppose you climbed to the top of a ladder that's about 300 miles tall. You would be up in the vacuum of space, but you would not be weightless at all. You'd only weigh about fifteen percent less than you do on the ground. While 300 miles out in space, a 115lb person would weigh about 100lb. Yet a spacecraft can orbit 'weightlessly' at the height of your ladder! While you're up there, you might see the Space Shuttle zip right by you. The people inside it would seem as weightless as always. Yet on your tall ladder, you'd feel nearly normal weight. What's going on?
    The reason that the shuttle astronauts act weightless is that they're inside a container which is falling! If the shuttle were to sit unmoving on top of your ladder (it's a strong ladder,) the shuttle would no longer be falling, and its occupants would feel nearly normal weight. And if you were to leap from your ladder, you would feel just as weightless as an astronaut (at least you'd feel weightless until you hit the ground!)
    So, if the orbiting shuttle is really falling, why doesn't it hit the earth? It's because the shuttle is not only falling down, it is moving very fast sideways as it falls, so it falls in a curve. It moves so fast that the curved path of its fall is the same as the curve of the earth, so the Shuttle falls and falls and never comes down. Gravity strongly affects the astronauts in a spacecraft: the Earth is strongly pulling on them so they fall towards it. But they are moving sideways so fast that they continually miss the Earth. This process is called "orbiting," and the proper word for the seeming lack of gravity is called "Free Fall." You shouldn't say that astronauts are "weightless," because if you do, then anyone and anything that is falling would also be "weightless." When you jump out of an airplane, do you become weightless? And if you drop a book, does gravity stop affecting it; should you say it becomes weightless? If so, then why does it fall? If "weight" is the force which pulls objects towards the Earth, then this force is still there even when objects fall.
    So, to experience genuine free fall just like the astronauts, simply jump into the air! Better yet, jump off a diving board at the pool, or bounce on a trampoline, or go skydiving. Bungee-jumpers know what the astronauts experience.
    Space isn't remote at all. It's only an hour's drive away if your car could go straight upwards. --Fred Hoyle CORRECTED: For every action, there is not an equal and opposite reaction.
    Newton originally published his laws of motion in Latin, and in the English translation, the word "action" was used in a different way than it's usually used today. It was not used to suggest motion. Instead it was used to mean "an acting upon." It was used in much the same way that the word "force" is used today. What Newton's third law of motion means is this: For every "acting upon", there must be an equal "acting upon" in the opposite direction. Or in modern terms... For every FORCE applied, there must be an equal FORCE in the opposite direction. So while it's true that a skateboard does fly backwards when the rider steps off it, these motions of "action" and "reaction" are not what Newton was investigating. Newton was actually referring to the fact that when you push on something, it pushes back upon you equally, even if it does not move. When a bowling ball pushes down on the Earth, the Earth pushes up on the bowling ball by the same amount. That is a good illustration of Newton's third Law. Newton's Third Law can be rewritten to say: For every force there is an equal and opposite force.
    Or "you cannot touch without being touched."
    Or even simpler: Forces always exist in pairs.
    CORRECTED: Ben Franklin's kite was never struck by lightning
    Many people believe that Ben Franklin's kite was hit by a lightning bolt, and this is how he proved that lightning is electrical. A number of books and even some encyclopedias say the same thing. They are wrong. When lightning strikes a kite, the electric current in the string is so high that just the spreading electric currents in the ground can kill anyone standing nearby, to say nothing of the person holding the string! What Franklin actually did was to show that a kite would collect a tiny bit of electrical charge-imbalance out of the sky during a thunderstorm.
    Air is not a perfect insulator. The charges in a thunderstorm are constantly leaking downwards through the air and into the ground. Electric leakage through the air caused Franklin's kite and string to become charged, and the hairs on the twine stood outwards. The twine was then used to charge a metal key, and tiny sparks could then be drawn from the key. Those tiny sparks were the only "lightning" in his experiment. (He used a metal object because sparks cannot be directly drawn from the twine; it's conductive, but not conductive enough to make sparks.)
    His experiment told Franklin that some stormclouds carry strong electrical charges, and it implied that lightning was just a large electric spark.
    The common belief that Franklin easily survived a lightning strike is not just wrong, it is dangerous: it may convince kids that it's OK to duplicate the kite experiment as long as they "protect" themselves by holding a silk ribbon and employing a metal key. Make no mistake, Franklin's experiment was extremely dangerous. Lightning goes through miles of insulating air, and will not be stopped by a piece of ribbon. If lightning had actually hit his kite, he would have been gravely injured, and most probably would have died instantly. See

    Yep, the framework agreement that had their nuclear program frozen, fell apart in 2002/2003 when W started a war on false pretenses and grouped NK in the “axis of evil.” First nuclear tests were three years later.

    Looking down from the International Space Station, those lights are the North Dakota oil fields. The green arch, of course, is the aurora.

    Honda CR-V Honored as Motor Trend 2018 SUV of the Year November 28, 2017 Motor Trend has named the ever-popular Honda CR-V as its 2018 SUV of the Year.


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