Well, as long as we have the tide issue still open, I'd like to mention another fine point. On page 73, the book mentions that the tidal force of the Earth on the moon is 80 times that of the moon on the Earth. That is a result of the Earth being 80 times larger than the moon.

However, it depends upon what is meant by tidal force. Usually, it means the difference in gravitational force from one side of a body to the other. In that sense, it acts like the derivative of gravity, so it is proportional to the inverse third power of distance.

That is also proportional to the diameter of the body being acted upon. So, the tidal force on small bodies (like humans, or even large lakes) is vanishingly small. Since the moon has a quarter of the diameter of the Earth, the tidal force of the Earth on the moon is only 80/4 times the tidal force of the moon on the Earth.

On page 138 at the bottom, it is written:

"...(compare that to the largest nuclear bomb ever built, which had a yield of about 100 megatons)."

This is techincally incurrect.

The largest bomb ever built had a yield of 50 megatons (the Soviet, "Czar Bomba"). That same bomb, when planned, was set for a yield of 100, yes, but wasn't built to that standard. She topped off as a triple stager, yielding a mighty impressive 50 megatons- so powerful that when exploded, in Siberiria, she broke windows in Finland.

<font size=-1>[ This Message was edited by: Lord General MB on 2002-05-26 21:45 ]</font>

The Bad Aviator said:
johnwitts said:
John, when speaking of airplanes, the terms "lift" and "thrust" have specific meanings. While lift is a force, it is not thrust. Lift is the force on the wings that keeps the plane in the air. Thrust is the force of the engine (propeller, jet) pushing the plane through the air. This is the technical context that The Bad Aviator is using, and why he is correcting the BA.

Weight and drag are the other two components of the equations.

But aren't props just wings going round and round? A bit like helicopter rotors are big propellers turned 90 deg?

Yes, and no.

Propellers do have an airfoil profile in order to push air. But that does not make them a wing. Wings give lift, propellers give "push", or thrust.

Helicopter rotors are a lot more complex than just a propeller aimed up. They have lots of controls to stabilize the rotors and adjust the blade angles to provide the controlled lift, to steer, etc.

Look, we're talking about technical terminology as precise as "force", "acceleration", or "theory". "Thrust" has a specific meaning - the propulsion of the plane. If you want to talk about other pushes on different parts of the plane, refer to them as forces. It's the terminology of physics.

Theory has a precise definition?

Yeah, it's when you're not quite Drunk enough to be making an Hypothesis, but still Pickled Enough, to be in an Altered State, of Consciousness!

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If you Ignore YOUR Rights, they Will go away.

This is a very common misconception. While indeed there's a pressure difference between the top and the bottom of the wing, the result is a very small lift force that's only a small fraction of what's needed to balance the force of gravity pulling the plane down.
Essentially a plane flies because the wing pushes the air down (action), and the reaction force is the air pushing the wing up. See excellent web page "How the airplanes fly" at
http://www.allstar.fiu.edu/aero/airflylvl3.htm

to see what's wrong with popular Bernoulli folklor.

You know, if I didn't know any better, I might call that "pushes the air down" a "pressure".

Yeah, but you call that centrifugal effect a "force", too, so what do you know? [img]/phpBB/images/smiles/icon_wink.gif[/img]

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"Ask to understand, but don't challenge unless you have the knowledge."--NEOWatcher

The contents of this post are ©2009 by SeanF and may not be copied or retransmitted in any form without the express written consent of SeanF

On page 126 the Bad Astronomer wrote, referring to the May 2000 planetary alignment, "Just a few months into the new century we had to deal with yet another instance of the shadow of our primitave need to blame the skies." The new century began with 2001. By the same reasoning that the second term of a president's reign begins with year 5, or the second week in the month begins with day 8.

http://aa.usno.navy.mil/faq/docs/millennium.html
Dana

<font size=-1>[ This Message was edited by: Dana_Mix on 2002-08-17 17:45 ]</font>

Holy mackeral! That's a very good catch, and I am very embarrassed by that one.

The third printing is already at the publishers (they were backordered 1500 copies out of 4000!), so I'll have to get that one in for the fourth. Thanks!

Not everybody agrees with that. In fact, I'm going out on a limb and say that most people don't agree with that. The USNO site is strictly opinion, when it comes to the millennium, and is not official.

I'm hoping that this does not turn into an interminable debate on the subject. Perhaps we should start a new thread--and I think it should be only new info not already presented at the USNO site that Dana_Mix linked.

But. The second year does begin with year 5, and the second week with day 8. Did you mean year 6 and day 9?

Consider the sentences "There are no apple in my basket" and "There is no apple in my basket". To me the first is correct and the second is faulty. The application of the word "no" has the same meaning as the word "none" in the sentence under discussion so I would go with the word "are".

Phobos

On the date-of-the-millennium question, the late Steven Jay Gould related an interesting story.

He discussed the issue with a savant, who could barely tie his shoelaces but was a whiz at dates -- telling you the day of the week for an arbitrary date in the year 8726, and the like.

Gould asked this fellow when the 21st century started. He answered without hesitation, "January 1st, 2000. The first century only had 99 years."

Not definitive, of course, but it's an interesting perspective!

Phobos, I think you're talking about the discussion at the bottom of page one of this thread?

Donnie B., I responded in the thread Horse that wouldn't die.

By convention, if nothing else, the following sentences are correct in modern English: "There are no apples in my basket" and "There is no apple in my basket."

I think it's called "agreement of number."

It's the same as if you were to say "There are two apples in my basket" or "There is one apple in my basket." The number has to agree. "Are" applies to the plural "apples" and "is" applies to the singular "apple."

Um...

Or am I beating a dead horse?

Anyway, the sentence "There are no apple in my basket" is a violation of the rules of standard formal English as understood at this space-time coordinate.

Silas

Whoa, didn't even catch that the first time. Phobos, are you really saying that "There are no apple in my basket" is correct, and that is not just a misprint (maybe it should be "there are no apples in my basket)?

The second week begins with day 8 and a president's second term with year 5, as I said.

Most people think the new century began with AD 2000. But science sites, encyclopedias, and government sites are right. http://dir.yahoo.com/Science/Measure...rd_Millennium/

The first century began AD 1. The second began with AD 101, and the 21st with AD 2001.

but I'll be happy to debate it.

best regards,

Dana

It's a matter of opinion, only. There can't be a wrong or a right.

On p 37 of "Bad Astronomy" it says "There are 51120977 square kilometers of it, give or take a kilometer or two..." Shouldn't that be a "square kilometer or two...

Great book.

best regards,

Dana

question, are you talking in plural or singular? if plural then an 's' must be added to apple, and the first one becomes the better of the two sentances.
if it is singular then the first sentance is an awful sentance thus the second sentance is the better one by default.

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its amazing how in the space of a few months, the memory can be serverly damaged, and all that you once knew is now hearsay and you know.... notmuch.

i'd like to note that scientists are never renowned for their english ability, and i would have thought that any publishers would have atleast four proof-readers two to simply read how the english goes together, and flows, and the other two to check the scientific side of things.

any writer will admit that the mind works quicker than the hand and they just want to put their ideas onto paper and upon re reading the written work they will miss things that shouldn't be missed but it is natural human nature for us to miss things, thats is why we get outside people to do the proof-reading. and thats just the english.

and so i congratulate BA on his book for having so few errors in his book, of which most appear to be mis-phrased sentances. so congratulations BA and i look forward to reading your book. (persuming i get it for my 17'th b'day next week)

chris

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its amazing how in the space of a few months, the memory can be serverly damaged, and all that you once knew is now hearsay and you know.... notmuch.

Thanks Chris! I hope you like it, and, of course, happy birthday. [img]/phpBB/images/smiles/icon_wink.gif[/img]

I am a scientist, but also a writer, and I try to write well. My grammar can be a bit awkward sometimes, but my wife's grammar is excellent. She always finds my subject/predicate mismatches. Also, there were a number of editors between me and the final book, yet some mistakes in grammar, typos and the like still got through. Oh well. Hopefully the fourth printing of the book will be as close to perfect as possible. I still have some errors to correct.

[quote]

Aircraft get their *unique* thrust from the Venturi effect.

Really?

I thought that it was Bernouli's principle
"Pressure of a fluid is least where velocity is greatest."

Venturi effect is what causes a downdraft of air into a carb. or into the vent pipes on a hot tub/spa... no?

[quote]
On 2002-09-19 22:22, nayland wrote:
The Venturi effect is a practical application of Bernouli's principle.

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T. Anderson

A question about "feeling" gravity. In BA, The Gravity of the Situation, p 68, you wrote in one paragraph:
In another paragraph on the same page you wrote:
I think this may be too nit-picky, but that almost sounds like you're contradicting yourself with respect to whether someone in orbit feels gravity. What you're trying to get across is pretty clear (the force of gravity is present, but is not perceived), but I'm still not sure if you consider it correct to say that astronauts in orbit don't *feel* gravity. I don't want to be responsible for passing along Bad Astronomy myself.

On page 181 near the top, it says:
We now know the surface of Venus has an incredibly high temperature, over 900° Celsius (1,600° Fahrenheit),

That seems too high for me Phil. The surface temperature of Venus, as I'm aware of it, is only as high as 900°F (480° C)

Anyway, enjoying the rest of the book very well. [img]/phpBB/images/smiles/icon_smile.gif[/img]

That's certainly what they say at Views of the Solar System and this NASA page, and Nine Planets says 740° K. Nice catch.

Maybe a little bit nitpicky, but it's a good point. The problem is that the BA uses the word "feel" in two different contexts. The astronauts don't feel gravity, as in sense it, but they do feel gravity, as in "have a passive experience of" it.

Yes, it is a bit confusing. I think the second one should be changed to "they experience gravity almost as strongly as we do" just to be a bit clearer.

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