The rules of a science-fair typically require that students follow THE SCIENTIFIC METHOD, or in other words, hypothesis-testing. The students must propose a hypothesis, test it by experiment, then reach conclusions. This supposedly is "The Scientific Method" used by all scientists.

Unfortunately this is wrong, and there is no single Scientific Method as such. Most scientists don't follow The Scientific Method in their daily work. "The Scientific Method" is a myth spread by school books. It is an extremely widespread myth, but this doesn't make it any more real. "The Scientific Method" is part of school and school books, and is not part of real science. Real scientists use a large variety of methods (perhaps call them "The Methods of Science" rather than "The Scientific Method.") Hypothesis-testing is one of these, but it certainly is not the only one, and it would be a mistake to elevate it above all others. We shouldn't force children to memorize it, and we shouldn't use it to exclude certain types of projects from science fairs.

There are many parts of science that cannot easily be forced into the "hypothesis/experiment/conclusion" mold. Astronomy is not an experimental science, and Paleontologists don't perform Paleontology experiments... so studying dinosaurs or stars must not be science? Or, if a scientist has a good idea for designing a new kind of measurment instrument (e.g. telescope), that certainly is "doing science", but where is The Hypothesis? Where is The Experiment? The Atomic Force Microscope (STM/AFM) revolutionized science. Yet wouldn't building such a device be rejected from many science fairs? It's not an experiment. The creators of the STM weren't doing science when they came up with that device? The Nobel prize committee disagrees.

Forcing kids to follow a caricature of scientific research distorts science, and it really isn't necessary in the first place.

Several sources claim that clouds remain aloft because the water droplets are too small to be affected by gravity. This is wrong. It doesn't matter if you break up a body of water into tiny droplets; its weight remains the same. If a cloud contains tons of water, it will be pulled to earth whether the water forms a cloud or whether it forms raindrops. Other sources claim that clouds stay up there because the droplets settle through the air very slowly. This is wrong too. Air that contains water droplets is actually far heavier than normal air (it's weight is increased by exactly the weight of the water droplets in the air.) Dense air falls fast! Professional meteorologists are saying these things. They should know better.

So why DO clouds stay up there? Why don't they pour downwards to form ground-hugging fog? The answer is simple. When liquid water condenses from water vapor, it releases thermal energy. When moist air turns into droplet-filled air, the droplets are warm, and they warm the air too. Clouds stay up there because they are just like hot air balloons. In fact, if the water droplets should 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 races upwards. This 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 races upwards at hurricane velocity!

Try making this "Touch The Clouds" device and you'll discover that droplet-filled air is very dense. You can easily pour it from a pitcher and fill some cups. But we also know that hot air rises. Mix the two together: dense air which is full of water droplets becomes less dense when heated, and at a certain temperature it should rise upwards even though it's full of heavy water droplets.

More thinking: helium rises in air, but liquid helium does not. Liquid helium is heavy (though not quite as heavy as an equal quantity of water.) This is because each gram of helium gas occupies a large volume, and it is bouyed upwards by the surrounding air. A volume of helium gas is lighter than an equal volume of air. Remember, less dense fluids will rise upwards through more dense fluids. So, what happens when helium condenses into liquid? It shrinks greatly, becoming more dense than air, then it dribbles downwards. It falls downwards even if it takes the form of tiny droplets. THE SAME IS TRUE OF WATER. H2O gas or "water vapor" is slightly 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 SHOULD fall downwards. Even if the droplets are so tiny that they individually settle slowly, liquid water is heavy, so the droplets should drag the air downwards as they go. The dense, droplet-filled air can fall very fast, even though the individual droplets remain "stuck in the air" because of forces of viscosity.

But when vapor condenses to form droplets, it releases "heat of condensation" which causes the air to expand. The air can even expand MORE than the vapor contracts. When clouds form, they usually pour upwards, not downwards. They are a bit too hot, so they try to rise to a higher level.

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

Also: wings/lift webpage

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 and the upward force supports the craft. But like any airplane, a helicopter rotor is a moving wing, and it's this small 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.

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.

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 was 300 miles tall. You would be up in the vacuum of space, but you would not be weightless at all. You'd only weigh fifteen percent less than you do on the ground. When 300 miles out in space, a 200lb person would weigh 170lb. 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 would 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 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." If we drop a book, does gravity stop affecting it, should we say it becomes weightless? If so, then why does it fall? "Weight" is the force which pulls objects towards the Earth, and this force is still there when objects fall.

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.

Many people believe that Ben Franklin's kite was hit by a lightning bolt, and this is how he proved that lightning was 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 electric 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 Franlkin that some stormclouds carry strong electrical charges, and it IMPLIED that lightning was just a large electric spark.

A single prism can split a sunbeam into a rainbow. Many children's science books show how a second similar prism can be used to recombine the colors. This is incorrect, two prisms do not work as shown. Prisms of two DIFFERENT sizes can split and then focus the colors into momentary recombination at a particular distance. With THREE prisms in a special arrangement, the splitting and complete recombining of colors can be accomplished. But books which depict one prism splitting the colors and a second identical prism recombining the colors into a single white beam are in error, and are no doubt the source of endless frustration for those of us who try to duplicate the effect with real prisms.

Many books contain a incorrect experiment which purports to demonstrate that air has weight. A crude beam-balance is constructed using a meter stick. Deflated rubber balloons are attached to the ends, and the balance is adjusted. One balloon is then inflated, and that end of the balance- beam sags downwards.

Unfortunately this experiment lies. When immersed in atmosphere, the buoyancy effect makes full and empty balloons weigh the same. But then why does the above experiment work? The experiment secretly relies on the fact that the air within a high-pressure balloon is denser than air within a low pressure balloon. To illustrate the problem, try this instead: attach two opened paper bags to the balance, adjust it, then crush one bag so it contains little air. The balance WILL NOT MOVE. What does this teach your class; that air is... weightless?

Or, perform the balance-beam experiment again, but blow one balloon REALLY full so the rubber feels hard and the balloon is about to pop. Blow up the second balloon so it is ALMOST full, but still a bit stretchy. Try to keep the balloons the same size. Now the balance will show that, even though the balloons are nearly the same, the "hard" balloon is heavier. Does this teach misleading things to your class? No, instead it exposes the dishonesty of the original demonstration. In truth, balloons full of air do not weigh more than empty ones. However, COMPRESSED air weighs more than uncompressed air.

What if we lived underwater, how could we use the balance beam to measure the weight of water directly? The answer is that we cannot. If a full water-balloon and a collapsed water-balloon were compared underwater, the experiment would show that they weigh the same, which seems to prove that water is weightless. When underwater, a bag full of water weighs just the same as a flattened bag which contains nothing. The situation with air is identical: if we live our lives immersed within a sea of air, we cannot use a balance to easily detect the actual weight of the air. (In fact, a bathtub full of air weighs about a half kilogram, but we cannot sense this weight while living in an atmosphere.)

It's hard to teach the weight of water to the fishes. The water-balloons experiment only works if we lift the whole experiment out of the water. That we a water-filled balloon weighs far more than an empty one.

And so the "air balloon balance" experiment could only work correctly if it were lifted out of our ocean of air, and then operated in a vacuum environment. We humans are like fish underwater: we're not aware that our ocean of air has any weight.

What is the difference between a liquid and a gas? Both are "fluids", both can flow. Gases are USUALLY less dense than liquids, although gases under fiercely high pressure can approach the density of liquids, so that's not a good criterion. The main difference is that gases are a different phase of matter: a gas can be made to condense into a liquid form, and a liquid can be made to evaporate into gas. Another major characteristic: because there are bonds between its particles, when a liquid IS PLACED INTO A VACUUM ENVIRONMENT, it will not expand continuously, while a gas in a vacuum chamber will expand continuously until it hits the walls.

This is very different than the oft-quoted rule that "gases always expand to fill their containers." This rule only works correctly if the container is totally empty: the container must "contain" a good vacuum beforehand. However, we all live in a gas-filled environment. All our containers are pre-filled with air. In our environment, any new quantity of gas will not expand, it will just sit there. If you squirt some carbon dioxide out of a CO2 fire extinguisher, it will not instantly expand to fill the room. Instead pour downwards and form a pool on the floor. It behaves similarly to dense sugar-water which was injected into a tank of water: it pours downwards, and only after a very long time it will mix with the rest of the water. "Mixing" is very different than "expanding to fill!" The rule about gases does not involve mixing, instead it involves compressibility and instant expansion into a vacuum.

Some books point to surface roughness as the explanation of sliding friction. Surface roughness merely makes the moving surfaces bounce up and down as they move, and any energy lost in pushing the surfaces apart is regained when they fall together again. Friction is mostly caused by chemical bonding between the moving surfaces; it is caused by stickyness. Even scientists once believed this misconception, and they explained friction as being caused by "interlocking asperites", the "asperites" being microscopic bumps on surfaces. But the modern sciences of surfaces, of abrasion, and of lubrication explain sliding friction in terms of chemical bonding and "stick & slip" processes. The subject is still full of unknowns, and new discoveries await those who make surface science their profession

Infrared light is invisible light. When any type of light is absorbed by an object, that object will be heated. The infrared light from an electric heater feels hot because the light is EXTREMELY BRIGHT LIGHT. Just because human eyes cannot see the light which causes the heating does not mean that the light is made of some mysterious entity called "heat radiation." When bright light shines on an absorbtive surface, that surface heats up.

And this is no benign misconception. Those who fall under its sway may also come to believe that *visible* light cannot heat surfaces (after all, visible light is not "heat radiation.") Misguided science students may wrongly believe that warm objects emit no microwaves (since only IR light is "heat radiation"), even though hot objects actually do emit microwaves. Or they may believe that the glow of red hot objects is somehow different than the infrared glow of cooler objects. Or they may believe that IR light is a form of "heat," and is therefore fundamentally different than any other type of electromagnetic radiation.

In his book "Clouds in a Glass of Beer," Physicist C. Bohren points out that this "heat" misconception may have been started long ago, when early physicists believed in the existence of three separate types of radiation: heat radiation, light, and actinic radiation. Eventually they discovered that all three were actually the same stuff: light. "Heat radiation" and "actinic radiation" are simply invisible light of various frequencies. Today we say "UV light" rather than "actinic radiation." Yet the obsolete term "heat radiation" still lingers. Since human beings can only see certain frequencies of light, it's easy to see how this sort of confusion got started. Invisible light seems bizarre and mysterious when compared to visible light. But "invisibility" is caused by the human eye, and is not a property carried by the light. If humans could see all the light in the infrared spectrum, we would say things like this: "of COURSE the electric heater makes things hot at a distance, it is intensely BRIGHT, and bright light can heat up any surface which absorbs it."

Many textbooks have an erroneous diagram of the earth which shows a bar magnet within it, and the ends of this bar magnet extend to just beneath the earth's surface. These diagrams depict the magnet's field lines as radiating from spots on the earth's surface. This is very misleading. The earth's magnetic poles actually behave as if they're deep within the earth, down inside the core. The Earth's magnetic field does not come from a giant bar magnet, but if we IMAGINE that it does, then the imaginary "bar magnet" inside the earth is short, stubby, disk-shaped, and part of the iron core deep inside the planet.

The typical textbook diagram is incorrect, and there are NO INTENSE MAGNETIC FIELDS at the land surface near the earth's "north pole" and "south pole." If you stand at the Earth's south magnetic pole, metals aren't attracted to the ground more strongly than anywhere else. The Geomagnetic "poles" on the earth's surface are not places where the field is strong. They are simply the points on the landscape where the field lines are perfectly vertical.

Proper diagrams should instead show the field lines to be radiating from poles inside the earth's core. They should show the field lines around the northern and southern areas of the earth's surface as being approximately vertical and parallel, not "radial" like a spiderweb and not concentrated into special points on the surface.

Another error associated with the above: some books claim that the earth's field at the magnetic poles is much stronger than elsewhere. This is untrue. The field strength at the north magnetic pole above Canada is about the same as the field strength in Virginia! And the strongest field in the Earth's northern hemisphere does not appear at the north magnetic pole at all, the north pole actually has a weaker field than elsewhere. The strongest fields in the northern hemisphere are not in one but in two places: west of Hudson bay in Canada, and in Siberia.

It is not correct to say that "the waves in laser light are all in phase." When two light waves combine, they inextricably add together to form a new wave, they do not travel as two independent "in-phase" waves. The photons in laser light are in phase, but the WAVES are not. Instead, ideal laser light acts like a single, perfect wave.

When the light wave within a laser causes atoms to emit smaller, in- phase light waves, the result is not "in phase" light. Instead the result is a single, more intense, amplified wave of light. In-phase emission leads to amplification. If the atoms' emissions weren't in phase, then the atoms would absorb light rather than amplifying it.

Each atom in a laser contributes a tiny bit of light, but their light vanishes into the main traveling wave. The light from each atom strengthens the main beam, but loses its individuality in the process. 99 plus 1 equals 100, but if someone gives us 100, we cannot know if it is made from 99 plus 1, or 98 plus 2, or 50 plus 50, etc.

All the *PHOTONS* in a single wave of light are in phase. This might be one reason that people say that laser light is "in phase" light. However, in-phase photons are nothing unique, and they don't really explain coherence. Any EM sphere-wave or plane-wave is made of in-phase photons. For example, all the photons radiated from a radio broadcast antenna are also in phase, but we don't say that these are special "in phase" radio waves, instead we just say that they are waves with a spherical wavefront. Even if all the photons in laser light are in phase, it is still incorrect to say "all the WAVES are in phase." Photons are not waves. They are quanta, they are particles, and they do not behave as small, individual "waves." Yes, all the photons are in phase, but only because they are part of a single plane-waves.

Light from most lasers is not parallel light. However, if laser light is passed through the correct lenses, it can be formed into a tight, parallel beam. The same is not true for light from an ordinary light bulb. If light from a light bulb was passed through the same lenses, it would form a spreading beam, and an image of the lightbulb would be projected into the distance. Laser light can form beams because a laser is a pointsource, and when you project the image of a pointsource into the distance, you form a narrow parallel beam! However, it is simply wrong to state that laser light is inherently parallel light. Laser light can be FORMED INTO parallel light, while the light from ordinary sources cannot.

Most types of lasers actually emit spreading, non-parallel light. Lasers in CD players and in "laser pointers" are semiconductor diode lasers. They create cone-shaped light beams, and if a parallel beam is desired, they require a focusing lens. The same is true for the lasers in inexpensive "laser pointers." Take apart an old laser-pointer, and you'll find the plastic lens in front of the diode laser inside.

In-phase emission causes the AMPLIFICATION of light, it doesn't cause coherent light. Because the atoms emit light in phase with incoming light, they will amplify the light, but they amplify incoherent light too, and they don't make it coherent. The coherence of laser light has another source... Laser light has two main characteristics: it is "monochromatic" or very pure in frequency (this also is called "temporally coherent.") Laser light also has a point-source character of sphere waves and plane waves (also called "spatially coherent.")

Even fairly advanced textbooks fail to give the real reason why laser light is spatially coherent. They usually point out that the laser's atoms all emit their light in phase, and pretend that this leads to spacial coherence. Wrong. It is true that the fluorescing atoms in a laser all emit light that's in-phase with the waves already traveling between the mirrors. But the in-phase emission only creates amplification of the traveling waves, it does not create spatially coherent light. For example, if you were to feed incoherent light into a HeNe laser tube, the atoms would emit in-phase waves, and the laser would amplify the light. But the brighter light would still be incoherent! Lasers certainly can amplify the COHERENT wave which is trapped between their mirrors. But how did the light within the laser get to be coherent in the first place?

Lasers create coherent light because of their mirrors.

The mirrors in a laser form a resonant cavity which preserves coherent light while rejecting incoherent light. How does it work? Imagine a simplified laser having flat, parallel mirrors. As light bounces between the mirrors, the light "thinks" that it's traveling down an infinitely long "virtual tunnel". (Have you ever held up two mirrors facing each other? Then you've seen this infinite tunnel.) When a laser is first turned on, it fluoresces; it emits light which is NOT coherent. Different random light waves start out from different parts of the laser. After a few thousand mirror bounces, all the waves have added and subtracted to form just one single wave. In the case of flat-mirror lasers, this wave is a nearly perfect plane wave. A single plane wave is coherent (to be incoherent, you must have at least two different waves.)

This can be a bit confusing. After all, the individual atoms each emit a wave. Don't all these waves add up to messy incoherent light? No. The in-phase emission preserves coherence as it amplifies. It's true that each atom emits light waves in all directions. However, these sideways waves cancel each other out, and only the waves that travel in the same direction as the incoming light will be preserved. It's as if the atoms "know" which direction to send out a beam. But in reality, the atoms don't know this. Instead, they just emit a light wave which is in phase with the incoming light, and for this reason the wave from the atom will cancel out everywhere except in a line with the incoming light. If the light in a laser was ALREADY coherent, then the atoms will amplify it but won't make it more coherent. The coherence comes from the great distance that the light has travelled as it bounced between the mirrors.

A similar thing happens with starlight: starlight is coherent! Starlight travels far from its original source and all the waves add up to form a wave with a single wavefront. Light from distant stars is spatially coherent, even though sunlight is not, yet the sun is a star. The farther the light travels from its source, the more it approaches the shape of a perfect plane wave. And a perfect plane wave is perfectly coherent. Laser light is spatially coherent because, among other things, the bouncing light has traveled millions of miles between mirrors, and all the various competing waves have melded together to form a single pure plane-wave or sphere-wave.

P.S. The pure color (monochrome) laser light is ALSO created by the mirrors. Huh? Yes, but the reason for this is not totally straightforward (and it's quite a bit beyond the K-6 level of these webpages!)

Opposite poles attract. If we hold two bar magnets near each other, the "N" pole of one magnet is attracted by the "S" pole of another. If we suspend a bar magnet by a thread, the "N" pole of that magnet will point... toward's Earth's north! Something is wrong here. Shouldn't the "N" pole of a magnet point towards the "S" of the Earth? Alike poles should not attract. Either the "N" and "S" printed on all bar magnets is reversed, or the "N" and "S" on the Earth is backwards. Which is it?

Physics defines "N-type" magnetic poles as being the north-pointing ends of compasses and magnets. Wind an electromagnet coil, see which end points towards the north, and that end is the N pole of the electromagnet. Therefore, the magnetic pole inside the northern hemisphere of the Earth is a south-type magnetic pole. The Earth's northern magnetic pole is an S! It has to be this way, otherwise it would not attract the N-pole of a compass.