I too have a large nitpicking side, one which wants to make errors vanish everywhere. But if (for example) the K-6 textbooks were all repaired, then they'd look like the "Voice of God," and the public would unwisely start trusting them as authorities. In other words, the sad state of K-6 textbooks is a goldmine for true learning, and for teaching the skill of Thinking.

Unfortunately, it's the wrong explanation. As oxygen burns, the volume occupied by the oxygen does not just vanish, it is instead replaced by equal amounts of carbon dioxyde.

The reason that the water rises in the glass is that the candle HEATS the air in the glass, and some of it escapes from under the glass, thus explaning the bubbling you see in the water as the candle burns. When the candle burns itself out, the air still trapped inside cools down and contracts again, syphoning in a certain volume of water to make up for lost volume.

The first part of the article is correct but at the end you mix up "weight" with "gravity".

You wrote: "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 bcome 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."

Gravity is the force of the earth pulling you down (it is the force between masses according to Newton's law Fg=G (M1 M2)/sqr(R)) When you're standing on the ground you don't fall because the ground pushes back to your feet. When there is no acceleration (up or down) this normal Force is just as big as the gravitational force thus the result on your body is zero (F=m x a; F=0 -> a=0). According to Newtons third Law all Forcescome in pairs with the same size and opposite directions. (F action = - F reaction) Your weight is the Force opposite to and of the same size as the normal force hence: without acceleration in vertical direction your weight has the same size and direction as the gravitational force BUT THEY ARE NOT THE SAME!

When you are on a scale in an elevator the scale measures your weight. When elevator is standing still your weight is the same as the gravity. When the elevator is accelerating upwards your weight increases (the net force (F normal - F gravity) on your body accelerates your body upwards as well). When the elevator accelerates downwards your weight decreases (the net force (F gravity - F normal) on your body accelerates your body downwards as well). When the elevator falls down i.e. accelerates down with 9,8 m/(sxs) you fall along with the elevator. The net force on your body is then formed only by gravitation. The normal force on your body bcomes zero hence your weight is zero but the gravity is not!

I hope I wrote down something you can understand because I don't write in English very often.

http://www.physicsforumscom/showthread.php?threadid=9145

Here is another which appears in many science books and is slavishly taught by teachers but is just plain wrong.

The demonstration is to float a candle on water and then cover it with a jam jar. The water pulls up inside the jam jar as the volume of gas around the candle decreases so this is given as proof that the candle is using up the oxygen in the air. I have even seen it used to measure the proportion of Oxygen in air. Tosh!

Firstly a candle gives off (almost*) as much CO2 as it uses Oxygen so the volume should not change. Secondly, the observant will notice that the water does not rise until after the candle has gone out. What actually happens is that the heat of the candle expands the air which for a few seconds bubbles out of the jam jar - generally unnoticed. Then the flame expires due to lack of Oxygen and the water rises as the air in the jar cools and contracts. (I try to avoid saying the air is 'sucked in' for fear of getting into more controversy about air pressure and sucking vacuums - but I digress!)

In my years as a science teacher (Biology!) I have seen many staff and a good few books misunderstand this simple demo. Please feel free to add it to your website.

*As a humble Biologist my chemistry is a bit rusty but I recall that Carbohydrates when burned give off as much CO2 as they use up O2 (Respiratory Quotient = CO2/O2 = 1). Fats give off less CO2, (RQ = 0.7). I don't know the position with Candle Wax but beingorganic and not unlike Fat it may be that it has an RQ of less than 1. If this is the case it might be possible to conduct this experiment in a sealed chamber so that no gas escaped during the expansion phase and the gas volumes could becompared before and after the experiment when the gases had returned to room temperature. This would at perhaps show that some gas had been consumed but this is a long way from the amateurish demonstration which forms the basis of many students learning!

Excellent website...it is good to souind off against the bad science which abounds. If one more child tells me that they are going to put volts through a wire... !

Freddy Janse wrote:
> Hello William,
> 
> Thank you for answering my mail!
> 
> The error on weightlessness is in indeed the text you wrote about gravity
> (http://amasci.com/miscon/miscon4.html#grav)
> The first part of the article is correct but at the end you mix up "weight"
> with "gravity".
> 
> You wrote:
> "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 bcome weightless? And if you drop a book,
> does gravity stop affecting it; should you say it bcomes 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."

Sorry for mycomplaint but although it's a fact that
n/d -> infinity as d->0, (for any positive number, n, d positive) it is not true to say that
n/0 = infinity

If your statement was correct simple algebraric rules would break since it would follow that 0 x infinity = n for any value of n and so all numbers are equal.

Actually n/0 is undefined for all n Should I start a mathematics misconceptions page?

- balsa rubber band planes, while the wing is flat, it is curved, and the distance across the top isnt the same as that of the bottom. traced with a finger, it cant go though the wing to follow the shortest path, it must follow across the top to get to the trailing edge, unlike the case at the bottom, where your finger can go straight to the trailing edge from the leading edge.paper aircraft wings glide, not generating lift, because it traps/resist the downward motion of the body, like an inefficient parachute. (flying squirel as example)everything else that is designed and manufactured to fly from r/c aircraft,the wright flyer and on to the space shuttle has been built with a leading edge thicker that that of the trailing edge, and/or some degree of curvature for its wing.from a design standpoint wouldnt it be easier to design a flat wing for all aircraft? there must be some reason as to why designers havent done so from the 1900s on to now.and that reason must be insufficent lift production.

-thicker,more curved airfoils = more lift. yes fighters have really thin ,symetrical wings, and mustcompensate by having a higher takeoff speed to generate the necessary lift for takeoff. and they can fly upside dwn, but as mentioned in an usaf airshow manual (which for the life of me i cant find now) which describes the procedures/maneuvers for the pilots, they have to "apply needed backpressure" to "maintain a level attitude". meaning he/she uses the rear elevators to push/pull the nose of the aircraft up, thereby recreating a positve angle of attack for the leading edge of the wing.

- the effect of icing on an aircraft wings leading edge iscompletely ignored. something important must take place at the very front that the accumulation of ice deprives from an wing in flight that severly diminishes the amount of lift availible.(remember thecommercial airliner that crashed after takeoff into the potomac river some years ago?that was blamed on wing icing, something every pilot training textbook warns strongly against).if lift is solely the result of air impacting the bottom of the wing and whatever "magic" occurs over the top of the wing from air circulation, this passenger jet wouldnt have gone down.

-the bottom of the wing of the cessna 152 that i used for pilot training was indeed flat, and the top highly curved and thick, meaning high lift and relatively slow takeoff speed

I have a couple of questions. Please remember I am not a scientist! I'm sorry if I sound really ignorant.:

1) If a "bulb doesn't change electrons or extract stored energy from a battery," how does a battery get used up?

2) You mention that a "filled freightcar" analogy doesn't work for electrical energy any more than for sound waves. I've never been able tocompletely understand the concept of sound waves. Would an analogy of a bucket brigade work for sound waves? The air particles would then pass the sound vibrations from one to the next so that it reaches the ear at the speed of sound.

Intrigued by your discussion of the density of air and the balloons on the balance. When I was about 12, science teacher did two experiments to measure the density of air (instead of acomparison balance, he used a very sensitive electronic balance from the chemistry lab): One using a glass bottle and a vacuum pump, which gave a density close to thecommonly quoted figure, and one using a large plastic bottle which was crushed to expel the air, and which naturally enough gave a density far too low. Only recently did I realise what caused the discrepancy!

You mention the impossibility of using the balance experiment under water to measure the density of water. I suggest either (1) an empty balloon and a balloon full of air, and measure the negative effective weight, or (2) a rigid bottle of water and an identical bottle of air, measure the reduction in effective weight.

With regard to the Wing function, it occurs to me that although Bernoulli's equation does relate pressure change and fluid velocity, he never implied that increased velocity would couse reduced pressure. He only stated that they must coincide. Any specific volume of a fluid will only accelerate (change velocity) if the pressure on one side is different than that on the other. i.e. a pressure difference will cause a velocity change. I cant see any reason to assume that a velocity change could cause a pressure change, and because the opposite is true, I think it's rather unlikely. How could a velocity change be acheaved in a steady state flow gas system, without a pressure difference causing it in the first place?

I would state that all lift is a result of reaction only. If a wing accelerates air down, then the wing is pushed up. The resulting pressure changes above and below a wing are due to it accelerating the air mass. These pressure differences are the cause of the air increasing or decreasing it's velocity (As Bernoulli describes). Therfore the Bernoulli effect does not cause lift or play any part in its generation. The velocity differences are caused as the result of the pressure differences, which are the result of the lift generated.

I do take this with a grain of salt and I appreciate you trying to correct things... but like butchering Newton's third law is just not right. [ Heh. Well, Newton wrote in Latin. The english translation depends on the preferences of the translator. The common translation is simply common, but that doesn't mean it's authoritive. If we take the latin for "an acting-upon" to mean Force rather than Action, then Newton's 3rd law comes out differently. But if we don't dare change what he said, then we'd better be teaching the original latin. -billb] Sure Newton's law may be better worded another way, but that's the way he worded it and it DOES make sense, so long as you don't take it the WRONG way. It may not be good to re-word it for people and then tell us that your way is the way it SHOULD be worded... That's like re-writing Mozart and saying that your symphony is more correct than his original.

Science should simply be taken less literally and if you're confused about something, either rely on quantum physics or test it out yourself. Quantum physics would tell us to keep all possibilities open until they have been extinguished. "IF a cat is put inside a box, the cat is both alive and dead until you can prove otherwise."

Aircraft stay in the air because they accelerate enough air downwards to balance their weight. This is easily seen in helicopters, and even more so in VTOL aircraft. In fact it is easy to calculate the jet efflux of a Harrier (AV8A) and see that it matches the aircraft weight. This is accelerating the air from stationary to vertically downwards. Multiplying the air mass involved in each second by the exhaust speed gives the same numbers as multiply the aircraft weight by the acceleration due to gravity.

When flying horizontally the forces must also balance but the wing moves a much greater mass each second to a lower resulting vertical speed.

The bounelli effect works (where it exists) by producing a low pressure area above the wing. Air above that 'falls' into that causing it to add to the total mass being accelerated vertically. Thus a wing shape is more efficient than a symmetrical wing because it 'captures' a greater volume as it passes through the air.

Another aspect of flying is that it must also satisfy Boyle's laws of gas volume and pressure.

An aircraft's weight is ultimately supported by the ground. If we take an area of say one square mile then the weight of air above that is roughly 25 million tons at 14.7 lbs/sqin. If a 747 of 250 tons flies into that square then the total above that square bcomes 25,000,250 tons and the average pressure must increase to 14.700147 lbs/sqin. The only ways that the pressure between the aircraft and the ground can increase is if the temperature increases or if the amount of air is greater (Boyle). Thus it can be seen that the aircraft maintains this pressure by pumping air from above and around it into the space between it and the ground in order to produce sufficient increase in pressure to support its weight.

["Trailing edge theory" is overstated because it's a central part of simplified " circulation theory" appearing in introductory aerodynamics textbooks. The simplifed theory requires that there be no detachment of flowing air from the surface, and that the trailing edge of the wing be infinitely sharp. In that case the trailing edge determines the location of the rear "stagnation point", which determines the circulation, which entirely determines the lifting force. The leading edge generates lift of course, but only because the trailing edge tells it to do so, and the leading edge shape is totally irrelevant as long as no stall occurs. But real wings don't have razor-sharp trailing edges, and real wings are always partially in "stall," so the simplified theory is only an approximation. -billb]
PS one technique in the simulation of airfoil lift in a viscous or inviscid medium is to use convergent equations to determine the net effect on the mass of air at a point infinitely far behind the trailing edge. At this point the local effects of turbulence have been removed, and all that is left is the net effect.

http://amasci.com/miscon/miscon4.html