# Measured Against Reality

## Sunday, September 24, 2006

### 6 Commonly Believed Things That Are Wrong

1. Centrifugal force

There is a lot of confusion about this one. Some people think that the centrifugal force is what causes water to stay in a bucket when you spin it around or pushes you against the door when you take a sharp turn in your car. That’s completely wrong, but not helped by its name, which means “center fleeing”. Some people also call centrifugal force a fake force. This is also wrong. So what’s going on?

When something moves in an circle, it is accelerating. This acceleration is called centripetal, which roughly means “pointing toward the center”. Because acceleration is a vector, it needs a direction, and centripetal acceleration is always pointing toward the center of the circle, hence its name. Thanks to Newton, we know that F = ma, so when a mass accelerates there’s a force. But that force is not what pushes you out, because it’s actually pointed toward the center of the circle. So what’s going on?

Well, Newton also explained this one. What pushes you out is Inertia. Because your body resists changes in its direction, when it undergoes centripetal acceleration it wants to keep going in a direction tangent to the circle. That’s what pushes you against the door and keeps the water in the bucket.

So what about the “fake force” part? Well, in a normal reference frame, the centrifugal force doesn’t exist. But in a rotating frame, it most certainly does. So while we might not need it most of the time, examining forces from a rotating frame requires it. It’s not fake at all.

2. The sky is blue because of the ocean or space.

I cannot confidently say that this is a common belief everywhere, and I sincerely hope it isn’t, but when I was in high school a large number of people did believe it, and no one knew what really makes the sky blue. I won’t even go into why it’s idiotic to think this, because it’s so obvious, but the real cause is interesting and not very well known so I will elaborate on it.

The cause is known as Raleigh scattering. What happens is that the blue wavelengths of the light from the sun are absorbed and then radiated by the gasses in the atmosphere, while the rest of the spectrum remains unaffected. This radiation happens in all directions, meaning that the entire sky looks pretty much the same shade of blue. This is also why the sun looks yellow instead of white, enough of the blue end of the spectrum is removed for it to appear yellow.

It also affects sunset, causing more of the shorter wavelengths to be filtered out as the sun’s light has to pass through more of the atmosphere to reach you.

3. Extra Dimensions

Most people seem to think that extra dimensions are some kind of world parallel to ours, or at the very least have a very muddled understanding of what extra dimensions entail.

Extra dimensions simply entail more coordinates to specify a location in space. For example, in one dimension, only one coordinate is needed to specify an exact location, x. Two dimensions needs two, x and y, and three needs three, x, y, and z. For everyone but String Theorists, we live in a world of four dimension, x, y, z, and t. That’s all that it means when someone says time is the fourth dimension, you need to give a time of an event along with its location in space to locate it exactly.

Anything above four dimensions requires the extras to be “curled up”, which means that they’re very small, so small that the only things that can move inside them are the most fundamental particles of the universe. In string theory, they take the form of Calabi-Yau manifolds, which are extremely complicated mathematical shapes. They occur at every point in space, and to completely specify a location you’d need to also give the extra 6 or 7 (depending on the theory) dimensions.

4. Nuclear power plants can explode like a bomb

I know some extremely intelligent people who believe this, and it’s rubbish. Nuclear power plants don’t have anywhere close to the fissile material needed for the runaway reaction like a bomb. Modern power plants can’t even meltdown like Chernobyl did. It’s actually a great irony of history that the same day that Chernobyl’s reactors overheated the same test was done here in the US, and the reactor passed with flying colors. Safeguards in place today make overheating virtually impossible. The pollution from coal plants is far more dangerous than nuclear power ever will be, but people seem so irrationally afraid of nuclear power that it doesn’t matter that it’s the safest and cleanest means of generating energy (at least once we have a good waste disposal plan, and there are many in the works).

5. Microwave ovens (or other electronics) can cause cancer

No, they can’t, at least without some serious malfunction. They don’t release as much dangerous radiation as a slab of granite. The number one source of radiation encountered by most people (unless you get an X-ray) is the ground. Even if you were to microwave yourself, the radiation wouldn’t give you cancer because it’s on the low-frequency end of the spectrum, meaning it doesn’t have the energy to knock DNA apart, unlike UV, X, or gamma rays. Microwaves do heat up water nicely though.

6. Medieval people thought the world was flat

No, they didn’t. This was made up more or less out of thin air by Washington Irving in his horrid biography of Christopher Columbus. I haven’t the faintest idea why this has become so widespread, since there is ample evidence going against it, but unfortunately it’s still taught.

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• I'll just point out that, theoretically, non-ionising radiation could, by heating your tissue, potentially cause cancer.

Maybe. Argh. I hate people who are scared of high voltage powerlines because of the word "radiation" in EMR.

• The thing about centrifugal force, though:

Yes, it's true that when looking at the bucket, or diagramming the entire system, centrifugal force does not exist.

Your final note on the topic is a very important one though: When analysing a system from within the a rotating device, centrifugal force DOES exist. In fact, it can be virtually (perhaps even competely, bit fuzzy on the physics here) indistinguishable from gravity, for example if you walk on the inside of a large spinning wheel in space.

In real world scenarios, you frequently calculate from the viewpoint of being inside the rotating device.

What pushes you against the side of the car door? Well, at that time, from your viewpoint? CentriFUGAL force.

I'm not saying that one can forget about centripetal. No basic understanding of physics is complete without understanding it. However, it's also important not to insinuate that centrifugal force is a falsehood that needs to be squashed somehow. You use one when analysing from within the rotating object, another from without. Simple as that.

• loved this post... I studied with a friend who insisted that the sky was blue because of the ocean - we were both studying in optics!

• I'm not disagreeing with you but genuinely curious... can you cite some examples that medieval people didn't believe the world was flat. I had always thought this was the case! I'm also still a little confused about centripetal / centrifugal force. Why does traveling in a circle require acceleration and not a constant rate of speed. Is it because of the change of direction?

By  Sam B, at 10:50 PM, September 25, 2006

• "Because acceleration is a vector, it needs a direction..."

Huh?
Acceleration is a vector. So it needs direction ?

Because butter is churned milk, it needs a cow ?

Nuclear power stations don't blow up ?
So what happened at Chernobyl ?

I bet you it passed all of it's safety checks before it went critical, causing a meltdown and subsequently blowing off the top of the reactor and most of the building around it.

OK, it wasn't an atomic fission reaction but it still blew up.

Next you'll try to tell me Edison invented the lightbulb or something like that ....

By  Anonymous, at 11:36 PM, September 25, 2006

• sam b, I did too, I think most people are taught that in grade school, as I said it was essentially invented by Irving. The Wikipedia article does a good job explaining it, but I first learned about it from Lies My Teacher Told Me by James Loewen, a book about misrepresentations of history in American schools. It's also been demolished on a few History Channel documentaries I've seen.

Anonymous, a has to have a direction, that's just part of the definition of vectors. And Chernobyl blew up because it overheated, generating too much pressure. The Uranium in nuclear reactors is enriched to something like 3%, while a runaway nuclear reaction need something like 90% (which is why the distinction is made between "civilian" and "military" enrichment). Also, modern reactors are designed differently from the one in Chernobyl, and it's nearly impossible for the same type of incident to happen because of mutliple fail-safes.

• Methinks you need to read "Flatland: A Romance of Many Dimensions".

By  Anonymous, at 12:09 AM, September 26, 2006

• Also, modern reactors are designed differently from the one in Chernobyl, and it's nearly impossible for the same type of incident to happen because of mutliple fail-safes.

Famous last words...

• cunt

By  Anonymous, at 12:17 AM, September 26, 2006

• Chernobyl blew up 25 years ago, but most nuclear reactors have working lifetimes longer than that. There are plenty of reactors older, and of similar design to chernobyl working around the world.
Chernobyl reactor would have been safe if the operators had followed procedure. (Although the reason why they needed to was kept secret from them).
The trouble with nuclear power is not that it is likely to have an accident, but that if it does the consequences are so bad.

By  Anonymous, at 12:33 AM, September 26, 2006

• Another good point is common law marriage in the U.S. Just because you live with someone for 7 years does not mean you are married by common law. There are many different tests that differ from state to state. You can reference the Wikipedia article on common law marriages.

By  Anonymous, at 12:55 AM, September 26, 2006

• The world isn't flat?!

By  Anonymous, at 1:06 AM, September 26, 2006

• Actually, other dimensions involve time and all the possibilities of that.

As for Chernobyl, it wasn't a nuclear reactor like we use in the west. So he is technically correct. We have so many redundancies in our reactors to prevent such a catastrophe.

• I think what Anonymous (above) meant to say was that Acceleration has direction and we therefore define it as a vector, as opposed to being a vector and requiring direction because of that.

By  Anonymous, at 1:33 AM, September 26, 2006

• you state that the sun is yellow because "enough of the blue end of the spectrum is removed to make it appear yellow"

my question is then:
why aren't pictures of the sun we recieve from satellites in space white? all pictures I've ever seen are yellow/orange

By  Anonymous, at 1:33 AM, September 26, 2006

• The great thing about this article: it's wrong about 5 of the 6 things it claims people are wrong about. I think we call this 'irony':

1. There is such a thing as centrifugal force. It is a *non-inertial* force, and can be measured in non-inertial, accelerating frames such as a rotating body. From the frame of reference of the rotating bucket, the force acting is clearly /outwards/ and everybody knows this to be true. The centrifugal force is what pushes the water towards the edge.

Just because a frame of reference is non-inertial, doesn't make the forces any less real. All frames of reference are relative. Ask Galileo, who invented relativity. (NOT Einstein).

2. The sky is blue because of the ocean or space.

I'm not sure if anyone believes that. But at least he's right.

3. He's wrong about dimensions too. Time is not a spatial direction, and is not treated as such. It is treated as a dimension of 3+1 spacetime, but it's an imaginary axis and therefore is not a spatial dimension in any strict sense.

Also, there's no requirement that extra dimensins *have* to be curled up. If anything, the notion is little more than a hack to explain why string theories postulate 11+1-dimensional universe when we live in a 3+1.

4. "Nuclear power plants can explode like a bomb": I know some extremely intelligent people who believe this, and it’s rubbish.

Balls. There's more than enough fissile material in a nuclear reactor to cause a thermonuclear explosion. In general use, the boron control rods absorb the excess neutrons, but if they were maliciously locked out of place...

5. "Microwave ovens (or other electronics) can cause cancer" No, they can’t, at least without some serious malfunction.:

Well, his intent is correct, but he overstates his case. Okay, the electromagnetic quanta that constitute microwaves are photons of a high wavelength and hence very low momentum. They cannot damage DNA directly, like gamma rays and x-rays can at the other end of the EM spectrum.

However, Microwaves can and do excite magentic dipoles in your body and cause a significant heating effect. We all know this from using a cellphone for an extended period. The long term effects of this rapid heating have not been studied significantly, so there's no basis on which to definitively state that they "do not cause cancer".

6. "Medieval people thought the world was flat." No, they didn’t.

Again, wrong. It rather depends who you asked. Okay, so the rare, educated elites in Europe believed in the Aristotelian geocentric model. But they were the elites. The significant majority of uneducated peasants believed in a flat Earth, because they had no reason otherwise.

Also implicit in this stated wrongness is that "all people = Europe". There were people outside Europe during the medieval period, many of whom had a variety of different solar system models. The most dominant of which was a flat-Earth hypothesis.

There. 5/6 wrong in an article about how people are wrong about science. Everyone point and laugh.

• I'm pretty sure Russian technicians back in the day would have told you that a meltdown at Chernobyl (or any plant for that matter) was very very unlikely or even unimaginable. Titanic couldn't sink either, remember?

By  Medjeti, at 1:48 AM, September 26, 2006

• Why chernobyl blew up is because it used coal and not water to seal the reaction. When something malfunctions in a modern nuclear plant the water immidiatly halts the reaction preventing any disaster.

• Anonymous, Chernobyl didn't blow up like a bomb, it blew up like a steam boiler and then burned like a heap of coal.

Stupac, nuclear plants of sane design (PWR, BWR and most others, even the russian VVER, but not the russian RBMK) indeed cannot blow up like Chernobyl did, and that's not because of multiple fail safes, it's because of physics. The power transient that blew Chernobyl apart is impossible in a water moderated reactor.

By  Anonymous, at 2:07 AM, September 26, 2006

• the sun appears yellow because it's a yellow star.. it's peak radiation is in the yellow wavelength... believe it or not there are red and green (etc) stars..

By  Anonymous, at 2:07 AM, September 26, 2006

• While it's true that a uranium reactor is pretty safe, not all reactors use uranium. Some nuclear reactors use plutonium; these are typically small scale & used for research. These reactors can blow up; the amount of plutonium necessary to maintain a fissile reaction is *very* close to that needed for a bomb.

• "I bet you it passed all of it's safety checks before it went critical"

Chernobyl blew up because most of the safety checks and procedures were disabled or ignored. Plus an inherent lack of understanding about why those procedures and checks were there in the first place.

You could say it blew up because of human stupidity. They build reactors in such a way now that you can't ignore or disable these checks and procedures amongst other things.

http://www.chernobyl.co.uk/causes.html

*I don't think it really blew up, the reactor melted down and the heat pressure blew the concrete container off.

• Thanks for clearing some of those up!
I was taught that medieval people thought the world was flat. They should stop teaching it

• This Blogpost is unscientific because it presents standpoints as facts and doesn't even provide references for these so claimed facts (I am refering to nuclear energy exclusivly). I hypothize that the author does this in order to manipulate it's readers to like nuclear energy.

Safeguards in place today make overheating virtually impossible.
Yeah, like the forsmack nuclear reactor in Sweden, which overheated this year because safeguards did't work. http://en.wikipedia.org/wiki/Forsmark_Nuclear_Power_Plant#July_2006_incident

The pollution from coal plants is far more dangerous than nuclear power ever will be

Yeah, riiight... http://en.wikipedia.org/wiki/Chernobyl_disaster

people seem so irrationally afraid of nuclear power that it doesn’t matter that it’s the safest and cleanest means of generating energy

Hellooooo, actually this is not a fact - it is just one side of a debate. Obviously it is not anywhere near as safe as windpower, waterpower, bio gas or solar engery.

at least once we have a good waste disposal plan, and there are many in the works
We are producing nuclear waste for more than thirty years and still have no plan ready for gettig rid of the waste? Maybe we should burry it underground so that no one can find it, oh wait... !

• With regards to the blue sky, the opposite is true though: The oceans are blue because they reflect the colour of the sky. As you all know, water has no colour. When you see green oceans, it's because the sky is blue, and the sandy bottom is yellow, and yellow + blue makes green. So there. :)

• Joseph Swan invented the light bulb!!!

By  Anonymous, at 2:47 AM, September 26, 2006

• I guess the Microwave thing is that we associate "radiation" with other bad stuff. All things considered, I think most people would rather trust a stove element than a microwave when it comes to random ailments. Can't blame people for that I guess.

• "but people seem so irrationally afraid of nuclear power that it doesn’t matter that it’s the safest and cleanest means of generating energy (at least once we have a good waste disposal plan, and there are many in the works)"

Solar and wind energy are much safer and cleaner...
also the disposal plans currently "in the works" includes digging out a mountain and filling it up with waste, don't try to convince the lesser that nuclear power is what they said it should be back in the '50s

By  Anonymous, at 2:50 AM, September 26, 2006

• wrt centrifugal force. My science teacher always insisted that we thought of 'the centrifugal effect' caused by centripetal force. The centripetal force is the force acting on the body towards the centre of the circle.

When you go round a corner in a car you feel the 'equal and opposite reaction' from the car door as you get thrown against it. You don't feel yourself pushed against the door, you feel the door pushing against you!

By  Anonymous, at 2:58 AM, September 26, 2006

• Chernobyl blew up because of the scientists doing new researches. All of them leave after recognizing that carbon bars are not going to return into holes in the reactor to slow down the raction because of the heat(holes shrinked too much). They said nothing to other workers! Belive me or not but I had to drink some terrible drink (lugol's water or something like that) when I was 6.It blew up about 500-600km from me. The fact is that russian(now ukrainians) egs available on the street market in poland emited light (some kind of LEE instead of LED).

• "Even if you were to microwave yourself, the radiation wouldn’t give you cancer..."

No, but you would probably boil to death. As you say: They heat up water very well and as most humans consist mainly of water... that would be quite an unpleasant experience.

By  Anonymous, at 3:15 AM, September 26, 2006

• To By Anonymous, at 2:36 AM, September 26, 2006

Btw, before writing anything about Chernobyl, I suggest you gather more information. The station did blew up and it did not passed all the safety checks, because they where simply turned off. There is plenty of details available on the Internet if you are interested.

By  Jurz, at 3:16 AM, September 26, 2006

• #1 - Correct!
Well done!

#2 Raleigh scattering is behind the colouring of sunsets, not the sky.

#3 Time is not a spatial direction, and is not treated as such. It is treated as a dimension of 3+1 spacetime, but it's an imaginary axis and therefore is not a spatial dimension in any strict sense.

#4 There's more than enough fissile material in a nuclear reactor to cause a thermonuclear explosion should the boron rods fail.

#5 Microwaves can and do excite magentic dipoles in your body and cause a significant heating effect. We all know this from using a cellphone for an extended period. The long term effects of this rapid heating have not been studied significantly, so there's no basis on which to definitively state that they "do not cause cancer".

#6 It rather depends who you asked. Okay, so the rare, educated elites in Europe believed in the Aristotelian geocentric model. But they were the elites. The significant majority of uneducated peasants believed in a flat Earth, because they had no reason to think otherwise.

Research, good sir! Research!

By  Anonymous, at 3:17 AM, September 26, 2006

• "Also, modern reactors are designed differently from the one in Chernobyl, and it's nearly impossible for the same type of incident to happen because of mutliple fail-safes."

"Modern power plants can’t even meltdown like Chernobyl did."

"It’s actually a great irony of history that the same day that Chernobyl’s reactors overheated the same test was done here in the US, and the reactor passed with flying colors. Safeguards in place today make overheating virtually impossible."

"The pollution from coal plants is far more dangerous than nuclear power ever will be, but people seem so irrationally afraid of nuclear power that it doesn’t matter that it’s the safest and cleanest means of generating energy (at least once we have a good waste disposal plan, and there are many in the works)."

All you are repeating above is "we only make every error once". That is certainly very good to start with, but it doesn't at all lead to a conclusion that nuclear power is safe.

It is only safe up to the point where all security measures are operated as planned, and where only known and expected incidents do happen.

Problem is that both of these prerequisites are not garanteed, and that the consequences of a failure may be desastrous. That makes your claim look very plain to me.

By  Anonymous, at 3:38 AM, September 26, 2006

• @ sam b

Centrifugal force is a simplificaiton for the masses. Acceleration is defined as a change of velocity (direction in which something is moving). The bucket is always changing its direction, so it is accelerating.

@ anonymus
Acceleration is a vector, so it needs a direction and a magnitude. You can accelerate forewards, or you can accelerate backwards. It is still acceleration. Chernobyl popped because of a steam buildup.

By  Anonymous, at 3:49 AM, September 26, 2006

• additionally, the greeks knew the earth was at least curved, because you see the top of a ship as it comes over the horizon.

By  Anonymous, at 3:50 AM, September 26, 2006

• Scattering does not mean absorbed and reradiated. It means scattered, as in smaller objects bouncing of larger objects. If the sky were blue by your explanation, then it would still be blue on the horizon at sunset. See refs.
http://en.wikipedia.org/wiki/Raleigh_scattering

http://hyperphysics.phy-astr.gsu.edu/hbase/hframe.html

By  Anonymous, at 3:57 AM, September 26, 2006

• Very nice post.

Just one remark about the 3rd point. Although string theory sees the extra dimensions as "curled up", the M theory, an extension of it, actually indicates the possibility of "parallel universes", in which ours would just be a 3-brane in a spacetime with 11 dimensions. In a nutshell, and very badly explained, the universe (multiverse?) can be made of of branes with up to 10 spacial dimensions (1 dimension is the typical string in string theory). What we see as the entire universe can really be just one specific 3 dimension brane. Of course it's not proved yet, but it is a possibility.

By  Anonymous, at 3:58 AM, September 26, 2006

• Some friends of my father are engineers who specialize in radio waves for satellite communication. For fun, they tested how much radiation was leaked from the microwave. They found that it was nearly unmeasurable, as the body of the microwave is a very effective faraday cage (link to wikipedia article) for the wavelength used and dissipates all of the waves trying to escape. Now, that's not to say that the microwave wouldn't damage your DNA if, say, your hand were exposed to it (in the microwave oven itself) -- large local fluctuations in temperature caused by the microwaves hitting water molecules in your body could easily cause damage by physcal stress on the DNA molecules. The rest of the cell would be damaged, too, so cancer would be the least of your problems.

However, the microwave oven is designed to stop this. Look at the wire grid on the window of the microwave -- it has gaps of about 5 mm. Since the frequency used is about 2.4 GHz and the waves travel at the speed of light, that means the wavelength is about 12.5 cm (freq. = speed/wavelength). That means the grid is about 2 orders of magnitude (100 times smaller) than the wavelength, and therefore is very effective at absorbing the waves. The rest of the microwave is solid metal, which will absorb nearly all microwaves. Incidentally, cordless telephones operate around this frequency. But don't worry -- you need a very precise frequency to heat water (or anything) effectively with radiation, and the phones produce a whole spectrum, each at low amplitude and duration. It isn't nearly focused or powerful enough to cause any harm, either.

By  Anonymous, at 4:10 AM, September 26, 2006

• http://www.eskimo.com/~billb/miscon/miscon4.html#blu

The sky is blue because the color of air is blue.

And here is true complete list of Physics Misconceptions

http://www.eskimo.com/~billb/miscon/miscon4.html

By  Anonymous, at 4:11 AM, September 26, 2006

• It still blew up, didn't it? Define "explode" so that it doesn't include the Chernobyl incident somehow. Or "blow up". What you meant was perhaps "Nuclear reactors cannot turn into nuclear bombs"? Good post otherwise, but stop calling people idiots for not knowing things - since they probably have been taught the stuff in school. What you SHOULD be pissed off about is the fact that school doesn't teach you to learn yourself.

• Is "nearly" impossible enough?
Check the July 2006 incident...
Officially is was rated 2, but only because actually no radiation emitted. We were quite lucky though...

• Don't forget the 7'th commonly believed WTC take down by an airplane and fires.

It's funny how people laugh at people who believed in flat world and now just can't see the art of controlled demolition (or rather propaganda) in front of their eyes.

• Frighteningly, I remember our teacher telling our class in grade school that the sky was blue because of the Oceans. I asked him, "Then why is the Ocean blue" and he answered, "Because of the sky". Even at grade 3, I knew this made no sense, so I went home and asked my parents and I've known the correct answer since.

• I think the key point here is "nearly". Let's face it: you don't really know whether meltdown can occur with modern reactors. Nobody thought it could occur prior to Chernobyl either.

Only a couple of month ago, there was nearly a meltdown in a Swedish nuclear power plant. The president of the Swedish Nuclear Power Organization called the sitaution "very, very dangerous". After simulations of the events, it is not even understood why there wasn't a meltdown!

So enough with the hyperbole. If you think nuclear power is safe and that nothing resembling Chernobyl can ever happen again, fine. But don't go around branding people who have a contrary opinion as idiots, or include it in lists abouts thing that are Wrong with a capital W.

By  Anonymous, at 4:44 AM, September 26, 2006

• There's no point for anyone to believe you on point 6. You provide zero evidence and no logic at all. Also, you have very little credibility, if any, for people to just take your word for it.

• According to http://www.eskimo.com/~billb/miscon/miscon4.html#blu , the sky is blue because air is very very slightly blue tinted and you're looking through a lot of it. Of course neither it or this post provide sources so it's very difficult to tell which is correct.

Interesting anyway though.

• 7. Western Medicine is the only valid medicine there is.

Not true. Eastern, or Holistic medicine has been around for thousands of years, and has a remarkable cure rate. Essentially, this medical discipline requires that the person being treated apply his mind to effect the cure, and is helped in this by various practices. Japan, India, and China all have their therapies and curative practices.

Western medicine, which as not been around all that long, depends primarily on two things – surgery and drugs to effect cures. Drugs are pharmaceuticals, not natural drugs, but artificially created in laboratories, and as such, are usually potent and/or toxic, as well. Surgeries, we all understand, having someone we know undergoing the knife, or even with our own personal experiences. Surgery is not always effective, curative, or even necessary, but usually requires the patient to have faith in both the procedure and the doctor doing it.

There is that word again – faith. Eastern medicine requires that the person’s mind do the healing, which is usually effected by building faith (trust) in the procedure and the doctor who is administering the procedure or potent. Essentially, Western medicine is no different. If a person does not believe in the procedure or the doctor, he will probably not get well. If he believes, even if the procedure is ineffective or even unnecessary, he will likely be cured. All of which is to the bafflement and/or denial of the practitioners of Western medicine, but is seemingly well understood by practitioners of Eastern medicine.

Jesus himself understood this: “And Jesus said, ‘Go. Your faith has made you well.’”

• loved the comments here.....especially the 'nearly impossible' one in last post......i guess we should just watch this space!

By  Anonymous, at 6:13 AM, September 26, 2006

• 7 and 8 Commonly Believed Things That Are Wrong: You get a cold from being cold. We've all heard it said; "Dress warmly, you'll catch a cold."

A 'Cold', with its symptoms of a runny nose, sore throat, sneezing, etc., is caused by either a virus or by bacteria, and has nothing to do with the effects of being exposed to cold, and/or wet.

8. "Masturbation is bad for you and everybody else."

Well, no, it isn't. Masturbation is good for you. It will even keep you out of trouble if you are a horny teenager and want to enjoy sex without the risk of teen pregnancy.

By  Anonymous, at 6:41 AM, September 26, 2006

• Your description on centrifugal force is accurate, but I don't agree with your conclusion. For the exact reasons you describe, centrifugal force isn't a genuine force. It is a 'perceived' force. The 'rotating frame' is simply another way of putting this. It's like saying "if I ignore the true context and origin of this force, then it's a magical new force called 'centrifugal' ". It's interesting, and useful to understand in systems, but not strictly accurate. Centrifugal force is not a genuine force, it is a tool to understanding the true forces at play.

By  Dan, at 6:49 AM, September 26, 2006

• You say it's not centrifugal force, but then you don't explain what centrifugal for is..

You then claim that current safeguards in nuclear reactors "make overheating virtually impossible." I think this is a very gung-ho attitude, and it's simply your opinion / belief (ironic, since the title of your post is "commonly believed things"). While I agree that nuclear plants are some of "the safest and cleanest means of generating energy," I don't believe we can treat them as a non-issue issue yet. Don't try to pass opinion on as fact.

By  Duc, at 6:49 AM, September 26, 2006

• a vector must have a direction. stop making yourself look stupid by comparing churned milk with vectors. it doesn't make sense.

By  Anonymous, at 6:53 AM, September 26, 2006

• I seem to recall a TV show about the controversies around irradiated food (a process most people seem to think makes food radioactive, but all it does is sterilise it), where one of the opponents said that the irradiation process created formaldehyde (which is a carcinogen) in some meats. A proponent of irradiation stated that while formaldehyde was produced, the amounts were less than if the meat had been cooked in a microwave. Naively, one could infer from this that microwave oven could cause cancer via formaldehyde, but this assumes that the amounts produced are greater than the levels deemed safe for human consumption.

• "modern reactors are designed differently from the one in Chernobyl"

Not to pick a nit here but even older reactors in the US were designed differently. Most US nuclear power plants are "presurized water reactors"(PWR) where Chernobyl and many other Sovit reactors are "Boiling Water Reactors" (BWR). In a BWR the reactor is designed to operate with 12–15% of the water in the top part of the core as steam, resulting in less moderation. An additional disadvantage of a BWR is that the control rods must be inserted from bellow, and can hence not fall into the reactor under their own weight in case of a total power loss ( in most other reactor types the control rods are suspended from electromagnets, causing them to fall into the reactor if power is lost ). Basically a BWR is an inherently less safe design.

Some of my comments are from wikipedia, here are a couple links

http://en.wikipedia.org/wiki/Boiling_water_reactor

http://en.wikipedia.org/wiki/Pressurized_water_reactor

By  Chris (different from the other Chris above), at 7:04 AM, September 26, 2006

• "I bet you it passed all of it's safety checks before it went critical, causing a meltdown..." -Anonymous

A nuclear reactor operates critical. All that means is that each fission releases exactly enough neutrons to maintain the reactor at the existing power level. A SUPER-critical reactor produces more neutrons per fission than are necessary to maintain power, causing reactor power to rise. The accident at Chernobyl involved a PROMPT-criticality, meaning the reactor reached criticality with neutrons produced directly from fission, rather than from neutron precursor fission product decay. This is not a normal operating condition, and it only occured because Chernobyl was practically designed to fail. Every other power reactor in the world was (and is) designed to fail into a safe condition in order to prevent a catastrophic failure. Chernobyl was designed to produce fissile material for bombs first, and operate safely second. A failure like it IS NOT POSSIBLE with a modern power generating reactor. Period.

If you live in New Hampshire (or any other place with a large amount of granite) you will absorb far more radiation from the naturally occuring granite in one year than you will in your entire lifetime from the material released from Chernobyl. You get a relatively large radiation dose from a trans-oceanic flight due to cosmic radiation, several orders of magnitude higher than you would get in decades of living near a functioning nuclear reactor.

By  John Lorenz, at 7:13 AM, September 26, 2006

• So what if it's really hard for a nuclear reactor to explode. Although there are new designs that cannot, many current nuclear reactors can still theoretically explode. Just because it's not designed to explode doesn't mean it can't.

By  vipstar, at 7:13 AM, September 26, 2006

• The sky is blue explanation is only partly correct. Yes,
sunlight is Rayleigh scattered by the atmosphere, but the scattering is not for blue light alone. All wavelengths are scattered. The scattering rate is proportional to the inverse of wavelength to the fourth power. So shorter wavelengths (ie blue) are most likely, but green, orange red is also scattered.
So at sunset, when sunlight
is near the horizon, blue, green etc has already been scattered out, leaving red (long wavelength)

By  Ben Samuel, at 7:31 AM, September 26, 2006

• "4. Nuclear power plants can explode like a bomb"

No, but the continually accumulating and indescribably horrifying waste will never, ever ever go away. There is no such thing as safe fission.

"Microwaves do heat up water nicely though."

No, they don't, and they can cause the water to go from still to suddenly boiling with explosive force when you reach in to grab the cup.

• Another one - people think that the dark side of the moon is always dark. Of course this isn't true - during a new moon, the 'dark' side is actually full.

By  Anonymous, at 7:46 AM, September 26, 2006

• "Also, modern reactors are designed differently from the one in Chernobyl, and it's nearly impossible for the same type of incident to happen because of mutliple fail-safes."

There is a problem with this statement as is used to try to assert that nuclear reactors can NOT blow up. First, multiple fail-safes can NOT gaurantee an non-explosion, they just reduce the percentage that it could happen. Fail-safes fail, and that's why you have multiples of them.

The statement itself, "it's nearly impossible", counterdicts the idea that it IS impossible. It is nearly impossible for someone to win a lottery, but nevertheless it happens all the time given enough trials.

• The second part of the "sky is blue" explanation that isn't often discussed:

http://www.aip.org/isns/reports/2005/009.html

By  Anonymous, at 8:06 AM, September 26, 2006

• It may worth pointing out that the reason medieval people didn't try before to go to India from Europe travelling to the west was they knew very well it was "far far away".

Christopher Columbus did an extremelly bad job calculating that distance. It exagerated the estimated size of India and minimized the estimated size of Earth, and managed to convince spanish's queen that such a trip was feasible, against the advice of court scientists.

• http://www.veritas-ucsb.org/library/russell/FlatEarth.html

By  Anonymous, at 8:45 AM, September 26, 2006

• "*I don't think it really blew up, the reactor melted down and the heat pressure blew the concrete container off."

Umm, if heat and pressure removing concrete isn't an explosion I don't know what is...

• re: dark side of the moon.

The "dark" side of the moon is actually the side that we never see. The moon is locked in an orbit such that one revolution of the moon on it's axis is spread out over exactly one orbit of the moon around the earth. So, when the moon has orbited 180 degrees, it has also rotated 180 degrees, and thus the same part of the moon is always pointed toward the earth. so, you're correct, when there is a new moon, the moon is positioned between the earth and the sun so that the half that always faces us is not illuminated while the half that we cannot see from earth (the "dark" side) is illuminated. I don't know for certain, but I would be willing to bet that this belief is due to misinterpretations of old references made to the "dark" side of the moon when the word dark could just as well mean mysterious or unknown as without light, and those misinterpretations passed along.

By  Anonymous, at 9:13 AM, September 26, 2006

• re: dark side of the moon.

The "dark" side of the moon is actually the side that we never see. The moon is locked in an orbit such that one revolution of the moon on it's axis is spread out over exactly one orbit of the moon around the earth. So, when the moon has orbited 180 degrees, it has also rotated 180 degrees, and thus the same part of the moon is always pointed toward the earth. so, you're correct, when there is a new moon, the moon is positioned between the earth and the sun so that the half that always faces us is not illuminated while the half that we cannot see from earth (the "dark" side) is illuminated. I don't know for certain, but I would be willing to bet that this belief is due to misinterpretations of old references made to the "dark" side of the moon when the word dark could just as well mean mysterious or unknown as without light, and those misinterpretations passed along.

By  Anonymous, at 9:14 AM, September 26, 2006

• Nice site - glad I found it! :)

Ok... on with the commenting already.

Chernobyl had a melt down not a blow up. They don't even sound the same. ;)

Also as I think someone may have mentioned here every day folks in the medieval era did think the world was flat.

I imagine many of the sailors of the day (non-command / non-navigation regular crew types) shared that belief

anyway - nice site.
I'll check back again!

• Great post - it's always good to see a lot of discussion going on. Physics is pretty interesting stuff, I wish I'd done it at university. However, I'm still scared of power lines!

• 7th Commonly Believed Thing that is Wrong: gods exist.

• Reading the comments here it's like the clueless leading the clueless. Anyway, I'll just respond to one point in a post: "As you all know, water has no colour." Water is blue. Anyone who's bothered to look at or through a large body of water knows this. Water absorbs red preferentially over blue allowing blue light to be transmitted and hence giving it a blue colour. You can see a graph of the relative absorption here.

• My 2 cents:

1 Nuclear power plants can blow up yes.. but never like an atomic bomb (not to mention like a thermonuclear bomb... that requires fusion..) you need enriched uranium at a level that you'll never see at a power station..

By  Anonymous, at 9:54 AM, September 26, 2006

• http://en.wikipedia.org/wiki/Flat_Earth_Society

http://www.theflatearthsociety.org/forums/

• wow, you're so smart! I wish I could be as smart as you. I mean, these 6 things, you really have them nailed. I bet you get a nobel, or a pulitzer, or something in the very infintesimally near future. Probably RIGHT NOW. No! Just then! There, you probably already have the smart award in your hand! Probably collecting dust just as we speak.

Do try to recall that at some point in the past, you didn't know any of this trivia. So on behalf of humanity, I apologize for all the people who don't understand these 6 items nearly as well as you do at this exact moment. And on behalf of those who knew them long before, what took YOU so long?

Idiotic indeed.

By  Mr Smarty Smarterson, at 10:14 AM, September 26, 2006

• I just have to say... I love how "Anonymous" essentially reposted Martin's comments two hours later with barely any mods to try to look smart.

Loser.

By  Anonymous, at 10:38 AM, September 26, 2006

• Just want to clear this up...

A nuclear power plant exploding, (which, living a few miles from one and having looked into it, is possible, but far from plausible), is not a thermonuclear reaction. This word refers to a fusion reaction, while power plants use fission. Fusion releases more energy, which is why it is now the preferred bomb type. It is also much cleaner than fission, apparently. I refer you to the most recent Scientific American, which contains an excellent explanation of this technology.

By  Me, at 11:07 AM, September 26, 2006

• Education at Stanford (4 years) \$120,4800

Creating a Blog on Blogger: Free

Writing a post about "6 Commonly Believed Things That Are Wrong" without any solid proof but with lots of personal opinion: Free

Getting pwned by Martin in comments on your blog about "6 Commonly Believed Things That Are Wrong" in which you err on 5 out of the 6: PRICELESS

By  Anonymous, at 12:04 PM, September 26, 2006

• Martin is right. Good eye for irony, Martin.

By  Anonymous, at 12:04 PM, September 26, 2006

• what about esoteric dimensions? surely they can be discussed? being that the mind is part of the body, I think the part about extra dimensions is a cheap shot . why? because you're being anal about the semantics of it. most people I've ever talked to about "extra" dimensions are not referring to string theory or science at all, but about the unknown. the inconcievable. I realize this forum is based on things that can be explained, not things that can't be explained, but I think this is a jab at something you don't understand. I'm not saying I do understand everything or anything. what I am saying is there's not a scientific explanation for everything. scientific theory is changing all the time. just remember that. you don't really know that much, none of us do...

• 7. That the word "irony" means coincidence.

It is not ironic that the US reactors were being run through a test that simulated the Chernobyl accident - it was a coincidence.

Irony refers to a contrast or incongruity between what is stated and what is really meant or between what is expected to happen and what actually does happen.

By  Anonymous, at 12:58 PM, September 26, 2006

• I'm standing behind Martin.
(So I look clever too)..

Anyone want to disagree with us ;-)

• 6 Commonly Believed Things That Are Wrong

1. Gravity is a vector.

No it isn't. Gravity is a force of nurture. Like Chuck Norris.

2. Space exists.

No it doesn't. All of those pictures that NASA release are just very very good paintings.

3. Extra Dimensions

Are like the extra 10% free that you get with supersized
portions. They sure do curl up.

4. Nuclear powered plants can explode like a bong

No they can't. Once inhaled, the bong is effectively empty of combustibles.

5. Microwave ovens (or other electronics) can cure cancer

No they can't. I know a lot of highly intelligent people who think that. But it's wrong.

6. Medieval people thought the word was phat

No, they didn’t. Phat is a newly invented word. So there.

By  Anonymous, at 7:32 PM, September 26, 2006

• lol anyone play command and conquer Red Alert 2? You can air strike a Soviet Nuke Plant and create a huge explosion.

By  Anonymous, at 9:49 PM, September 26, 2006

• You forgot #7. Dinosaurs and humans have never coexisted.

By  Anonymous, at 11:07 PM, September 26, 2006

• I'm bored and it's late. So I'll post a reply to Martin's 5/6 wrong bit.

1. His comments about the water... ehh, it is centrifugal force that 'keeps' it in the bucket, due to the center fleeing of the water. But his comments of the car and centripetal force are correct. Same force that throws you off a merry-go-round. :)
So we'll do a 1/2 wrong here.

2. YAY! OK, I saw some posts about water not being blue... Water is blue. Find the post about absorbtion spectrum of water.

3. I think he goes off on unrelated material when he gets into string theory. BUT for time, to fully describe where an event occurred, time must be used. To say the event is in my living room, with no time, is saying the event is ALWAYS in the living room. But if you say at x,y,z,t there will be a flash of light, you know WHEN to be there as well as the location.
Pulling in time was a bad example, IMHO. It can be hard to understand with a common concept of time. It is just adding more coordinates. He shoulda stopped there. x,y,z,i,j,k. Look, 6 dimensions.
I'll go with 1/2 wrong for saying more than required (and no, extra dimensions don't have to be curled, quit the string theory).

4. There is more than enough radioactive material to cause a chain reaction, causing an explosion. The material is not close enough together to cause a chain reaction, so even under failure, an explosion won't happen. A melt down will. If the boron is locked outta place, the water will all boil off, the rods will get REALLY host and start to melt, melting the concrete, and then the concrete becomes an abosrber and prevents an explosion, but continues to heat and melt and release bad bad gas. So he's right here.

5. I'm sure anything can cause cancer if you get enough in the right place. :) For microwaves causing cancer... you are getting bombarded by higher energy waves all day every day. The focused content of a microwave would just give you a REALLY bad burn, I assume, possible deeper than just the skin.
If they cause rapid heating and rapid heating causes cancer, then it would be rapid heating causing cancer, which can come from many sources, not the EM itself.

6. His statement is correct. Medievial didn't think the world is/was flat. There is plenty of artwork and old maps that have a world representation as a round object or sphere.
I'll add the thought that is in my head, to me, and the only way I've ever head it refferenced, Medievial refferes to Europe during a specific time frame. So this may be a miscommunication of the word, but I've never heard of the chinese of that same time called Medievial people. So perhaps poor wording on it. Maybe 1/2, so 1/4.
If my math is right, he gets a 1.25 wrong from me. WEEEEE!!!!

By  Munki, at 11:12 PM, September 26, 2006

• RE: Nuclear Power Plants

quote: "It is only safe up to the point where all security measures are operated as planned, and where only known and expected incidents do happen."

This statement is factually untrue.

First: The safety measures in a nuclear reactor are all fully redundant, and in critical areas they are 3x redundant or more. Thus, "all security (read: safety) measures" do not need to operate as planned, just a unique subset of those measures.

Second: The risk analysis done for all nuclear reactor designs include large saftey margins for unknown events. Large impact events like earthquakes and plane crashes are included in the analysis, along with some estimation of anomolous events which may impact the plan.

Regarding other comments on Chernobyl - that plant experienced a chemical explosion, not a nuclear one. The explosion distributed a large amount of nuclear material over a large area, but it was not a nuclear explosion. As has been stated, modern nuclear power plants have passive safety measures, and thus even if all active safety measures fail the plant will not experience a nuclear explosion, but will simply shut itself down slowly. The worse that could happen would be melting in the core and the reactor housing is designed to contain that as well (as happened in Sweden.)

From reading the comments in this thread, it is clear that most people are unaware of the years of effort that go into the safety design and certification of a nuclear power plant. One would be far, far more at risk living next to a coal or natural gas power plant. Heck, flying and driving kill thousands of people a year, and yet I be you all still fly and drive! I recommend learning a bit more about risk assessment...

By  Anonymous, at 9:57 AM, September 27, 2006

• I'd also point out that dimensions can be though of as really just a set of variables usually denoting a state of something. Usually people think of them as classical temporal ortho-normal dimensions, which are used to denote a location in space. When you think of them as just variables you really can use any dimension you like, say "current number of bananas in Japan" or "the direction north by north-west from my cat Fuzzy", or just "the distance north-west of the origin rather than north of the origin in a 2d space", your dimensions don't have be ortho-normal or even make sense.

When looked at from this perspective it doesn't make sense to say things like, "we live in an n dimensional space". n really depends upon your current problem space and the how you want to look at it. In this context you could say we live in an infinite dimensional space.

• Yea so, Nuclear reactors can't blow up?!?!? Whatever, I watched live as our local Nuke plant blew up into hundreds of thousends of pieces befor our very eyes! :) Trojen Nuclear power plant was demolished and BLOWN up in Kalama Washingtion this summer! It was such a pretty pretty site! Now, if we can just destroy the Hanford Nuclear power plant and waste disposal sites in eastern Washington we'de be set!!!!

By  Anonymous, at 1:00 AM, September 29, 2006

• As a reseachers and someone whose work in the Zone of Alienation at Chernoybl I can say there are some pretty ignorant comments here. AS stated it's not possible for an RBMK pile to produce a nuclear explosion. The explosions at Chernobyl were not nuclear events. If all control rods were sudenly removed, even when operating at maximum designed power, there would be no nuclear explosion. The results wouldn't be pretty though.

By  Anonymous, at 6:16 AM, September 29, 2006

• I was a nuclear technician in the Navy on asubmarine. What drives me crazy is the use of the word "critical" when talking about nuclear reactors. No doubt Hollywood is the reason behind the wrongful use of this word. There are 3 terms used when talking about a reactor: 1)Sub-critical -reactor is shutdown and is producing minimal fission reactions. 2)Critical -reactor is producing fission reactions and being controlled by the control rods. This is the NORMAL operating state of the reactor. 3)Supercritical -this is the bad one. The fission reactions are out of control and will cause a MELTDOWN if not brought back under control. Reactors do not explode. The extreme heat causes the cooling water to become superheated steam which then is released with enough force to make the appearance of an explosion. The reactor itself becomes so hot that it melts, thus releasing the radiation from the core. Thanks for letting me "vent"

By  Anonymous, at 8:21 AM, September 29, 2006

• An old physics teacher of mine said that 'centrifugal force force is simply the lack of centripetal force.'

By  TH, at 8:29 AM, September 29, 2006

• One of my favorite misconceptions or Urban Legends is:

We only utilize 10% of our brain. I dont know what numbskull came up with this one, but I am pretty sure he is the ONLY one that only uses 10%. We might only use a small percentage for day to day activity, but the rest operates our autonomic functions and what not.

By  Matt, at 10:16 AM, September 29, 2006

• Re acceleration. Acceleration is a change in velocity. Velocity describes speed and direction. Acceleration can be a change in speed with no change in direction, a change in direction with no change in speed (as in travelling in a circle) or a change in both speed and direction.

Re the color of the sky: http://math.ucr.edu/home/baez/physics/General/BlueSky/blue_sky.html
It's more complicated than just Rayleigh scattering. (Note: Rayleigh NOT Raleigh)

Re centrifugal force. There are two types: the pseudo or fictitious centrifugal force is relevant to a rotating frame of reference. The reactive centrifugal force is the reaction to a centripetal force and is exerted by a rotating object upon the object causing the centripetal force. It is ever present and is independent of reference frame.

Re Medieval people. If you're referring to the "Columbus proved the world is round b/c EVERYONE thought the world was flat" myth, you'd be correct. The educated people in Europe did know that the world was round. (As noted above, those who lived near the ocean noticed that the top of a boat was visible as it came over the horizon. However, few undeducated people would have made a connection between this phenomenom and a round or curved earth.) To the landlocked and uneducated denizens of Medieval Europe, the flat world was only common sense. As it remains to many uneducated people today.

I agree with others here. If you're going to correct others, you should make sure that you're correct yourself.

• Um, wouldn't the number one source of radiation encountered by most people be the sky (not the ground)?
And, according to no less an authority than Bob Dylan, "The Sun ain't yellow, it's chicken!"

By  Anonymous, at 7:07 PM, September 29, 2006

• Sometimes I think it would take a 100 of you people to screw in a lightbulb. 1 to put the bulb in, and 99 to say "I could have done it better than that"!!!!!!!!!

By  Anonymous, at 12:51 PM, October 02, 2006

• Stuart,get a job,pay taxes, watch closely. Because the world as you know it now will look so much different by the time your 50 that this blog will have been a complete waist of your valuable living time. You young people need to back away from your screens and get some life experiences going. Instead you waist time hashing over the lives that everyone else is living. Good luck

By  Anonymous, at 1:07 PM, October 02, 2006

• Washington Irving was quite the "poet", or just a liar. He also expanded George Washington's Inagural oath to include "...so help me god", which GW never uttered, but try telling that to the religious zealots.

Irving's attempt to glorify Columbus' mission beyond its true goal, finding gold, was feeble, but believed by a very poorly educated lot on history; Americans. If Irving would have been truthful about Columbus and his cutting off feet to punish escaping native slaves, we wouldn't have another national holiday to be embarassed about.

By  Anonymous, at 5:41 PM, October 03, 2006

• Martin is no better then the original article creator himself(which I much enjoyed). There is no proof other then Martins "word". The fact is Martin wasn't even correct. #6 is 100% correct. The "majority" of people didn't believe the world was round so relax your pants Martin there is lots of proof out there that back this. Therefor Martin missed one (and who knows if I can trust him on the rest). How ironic.....! Overall you should be less critical. He was 75%-100% correct on all 6 things so relax.

By  humpacactus, at 11:32 PM, October 29, 2006

• i love all you people that use your brains!! keep it up,

and the sky being blue, when the sun sets why is the sky never green?? (the spectrum blue/green/yellow/red??)

and why is the sky on mars always red??? i'm gonna stick with the ocean's reflection story...

• Do you know anything about any negative side-effects of cell phones? Is there truly any risk of cancer, or is that a myth too?

By  Chris, at 4:44 PM, November 07, 2006

• Chris, from what I know there is no risk of cancer from a cell phone. Their signals transmit in the microwave range, which is not energetic enough to damage DNA. When concentrated Microwaves can heat water molecules, but the signal from your phone isn't strong enough to do that.

• I love #6. I suppose people conveniently forget man has known the world was round since at least Ptolemy.

How easy the masses are tricked. UCLA Professor of History Geoffrey Symcox's work on Columbus is great though; he does a fantastic job of detailing how a lot of what young Americans are taught about Columbus is complete BS.

Worth a read, IMO.

By  Anonymous, at 10:59 AM, May 01, 2007

• vRe: "4. Nuclear power plants can explode like a bomb"

Conventional plants, no.

But BREEDER REACTORS are an exception; it would take an extraordinary trouble to get to a real mushroom cloud event, but "impossible" is not accurate.

• "The Church says that the Earth is flat, but I know that it is round. For I have seen the shadow on the moon and I have more faith in the Shadow than in the Church." -Ferdinand Magellan

So either there were institutions in Europe promoting flat-earth belief, else Magellan was engaging in anti-church propaganda.

By  Anonymous, at 5:45 PM, August 26, 2007

• Magellan round earth quote

The quote is a fabrication of Robert Green Ingersoll. It is found in his essay “Individuality.” This may be accessed at http://www.infidels.org/library/historical/robert_ingersoll/individuality.html
It’s in the fourth paragraph of his essay:

It is a blessed thing that in every age some one has had individuality enough and courage enough to stand by his own convictions, -- some one who had the grandeur to say his say. I believe it was Magellan who said, "The church says the earth is flat; but I have seen its shadow on the moon, and I have more confidence even in a shadow than in the church." On the prow of his ship were disobedience, defiance, scorn, and success.

This was first pointed out, as far as I know, by Dr. Tom Gorski in his website “Knowing What Ain’t So” at http://www.churchoffreethought.org/cgi-bin/contray/contray.cgi?DATA=&ID=000011010&GROUP=048. Dr. Gorski is one of four founders of the The North Texas Church of Freethought.

Vicente Calibo de Jesus
ginesdemafra@gmail.com

• There are some complete idiots commenting on this blog. Coal power is far more dangerous than nuclear power. Every year the pollution from coal-fired power plants causes hundreds of thousands of deaths worldwide. The CO2 emissions contribute to global warming. You would get 100 times the radiation dose living next to a coal plant than you would living next to a nuclear plant. On a per TWh basis, nuclear is several orders of magnitude safer than coal. Indeed, it is difficult to calculate a meaningful deaths per TWh figure for nuclear because the number of deaths is so low. Chernobyl, a poorly designed, even more poorly managed, and now totally-out-of-date reactor killed a few dozen people. It did not blow up like a nuclear bomb. Nuclear reactors can't blow up like nuclear bombs. Modern reactors have numerous safeguards against meltdown. And for some of the next-generation nuclear reactors, meltdown is impossible.

As for medieval beliefs about the shape of the Earth, the overwhelming consensus among educated men of the time was that the Earth was spherical -- not flat. You can certainly find a few examples of medieval writers claiming that the Earth was flat, but the vast majority of their contemporaries rejected such nonsense. There is a book devoted to this subject: "Inventing the Flat Earth: Columbus and Modern Historians" by J.B. Russell.

• On an object moving in a circular path, there is no centrifugal force as viewed by an inertial observer.

Centrifugal force on such an object only exists for non-inertial observers.

However, both inertial and non-inertial observers recognise a centrifugal force from such an object, on whatever is keeping it in the circle.

Two different meanings:

Most standard physics textbooks use the "modern" meaning of centrifugal force as a pseudoforce, existing only as an artefact of viewing things in a non-inertial frame.

It is not a "real" (physical) force, since it has no agent.

The "old-fashioned" meaning of centrifugal force as the Newton's-3rd-law pair ("reaction force") of the centripetal force is completely "real", in any frame.

These two different types of centrifugal force act on different bodies.

• I'm a physicist and I just wrote a blog about cell phone and microwave oven radiation. Please check it out here:

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