SGU Episode 53
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| SGU Episode 53 |
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| July 26th 2006 |
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| (brief caption for the episode icon) |
| Skeptical Rogues |
| S: Steven Novella |
B: Bob Novella |
R: Rebecca Watson |
J: Jay Novella |
E: Evan Bernstein |
| Links |
| Download Podcast |
| Show Notes |
| SGU Forum |
Introduction
You're listening to the Skeptics' Guide to the Universe, your escape to reality.
News Items ()
Budget Increase for NASA ()
- news.bbc.co.uk/1/hi/sci/tech/4688532.stm
Indigo Children ()
- abcnews.go.com/GMA/AmericanFamily/story?id=2224795&page=1
Insanity for Andrea Yates ()
- Insanity for Andrea Yates
Questions and E-mails ()
Monkey Eating Eagle ()
Greetings from Milford, Ohio. We are just a hop, skip and a jump from the soon to be opened Answers In Genesis Creation Museum in northern Kentucky. (And it's about damn time. I want answers! But I digress.)
I'm still catching up on your podcasts having discovered them only recently so I am a bit behind you folks but I wanted to respond to the remark by your resident 'birdist', Perry, concerning monkeys and eagles. On your May 10th podcast he threw down the gauntlet to our avian friends by claiming any monkey could kick any bird's ass. Go to the URL below and repent, Perry!
boojum.as.arizona.edu/~jill/Cynthia/report.html
Love the show, by the way. Oh, and one more thing; who is the hot sounding Brit babe who introduces the podcast?
John Burris
Milford, Ohio
Bird flight ()
Dear Dr. Novella,
I am a big fan of the Skeptic's Guide to the Universe podcast. I eagerly await a new podcast each week. I think the addition of Rebecca to your table of 'esteemed skeptics' is a wonderful addition.
You mentioned on one podcast (I think the one where Eugenie Scott was a guest) that you attended Johns Hopkins and studied with Pat Shipman. I got my Ph.D. in Ecology and Evolution from Johns Hopkins and knew Pat as well. I graduated in 1982.
I appreciated the most recent podocast with Bill Bennetta. Textbook adoption is certainly in a sad state of affairs. I felt I should write because of Bill's comments about Bernoulli's principle and bird flight.
I am an ornithologist and teach ornithology regularly here at Colby College. My own research expertise is in the foraging behavior of birds and bird vocalization. I do however follow the literature on bird flight closely.
Bill stated that the importance of Bernoulli's principle for bird flight has been debunked for 40-50 years but still appears in textbooks. He argued instead for a mechanism where a flat bird wing pushes down on the air, elevating the bird.
I believe Bill's interpretation would be rejected by most ornithologists. Bernoulli's principle is alive and well in our understanding of bird flight.
To begin with, airfoils (the shape that best takes advantage of Bernoulli's principle) occur at different scales in birds. The cross-section of a wing is an airfoil, the cross-section of the major flight feathers (the primaries and secondaries) are also airfoils. Finally, the body of a bird with a blunt head and sloping body defines an airfoil.
Let's begin with the discuss of dynamic soarers like albatrosses and other tubenoses. These birds travel hundreds of miles a day over the ocean, scarecely flapping a wing. They turn into the nearly omnipresent ocean winds to gain lift via Bernoulli's principle and then turn downwind to glide.
If one wishes to argue that albatrosses glide rather than use powered flight, let's consider a bird like a goose. Slow-motion photography of a flying goose reveals that the inner part of the wing (the radius and ulna bearing the secondaries) stays remarkably level through a complete wing stroke. The distal part of the wing (the fused hand bearing the primaries) however pivots strongly, almost parallel to the dorso-ventral axis of the bird at the end of the downward power stroke.
The interpretation of this movement is that the distal part of the wing is acting as a propeller. We need to be aware that Bernoulli's principle does not depend on a particular orientation with respect to gravity. As the distal part of the wing is forced downward, Bernoulli's principle results in lower pressure on the anterior side of the distal wing and higher pressure on the trailing edge. The result then is a force parallel to the surface of the earth, namely thrust. As the bird moves forward because of this thrust, air rushes over the relatively stable inner wing. Bernoulli's principle here results in an upward force or lift. So, a bird's wing really consists of two parts, one of which can be rotated by about 90 degrees. Each part is shaped as an airfoil. Because of differences in orientation, the inner wing produces lift to counteract gravity and the outer wing produces thrush to counteract drag.
Bill's explanation of bird flight cannot explain the function of the alula feathers at the base of the hand. Those feathers act as an aerodynamic slot, allowing the angle of attack of the airfoil to be greater, thereby maximizing the pressure difference between the upper and lower part of the wing.
On take-off, birds use as high an angle of attack as possible to rapidly take-off. To land, birds tilt their wings to an angle of attack at which laminar flow no longer occurs across the top of the wing with the result of rapid loss of lift. In a controlled manner, birds set up a turbulent flow to allow themselves to lower gently to a perch.
I can refer you the Wikipedia entry on bird flight that I think is reasonably accurate: http://en.wikipedia.org/wiki/Bird_flight
You will note that one of the references cited in the Wikipedia article is Dave Alexander's book on animal flight. Dave received his Ph.D. about 20 years from Duke where he worked with Steve Vogel and Vance Tucker. These two scientists are superb biomechanics, certainly among the most eminent in the country. Dave is a leading authority on powered flight.
The explanation I present above and described in the Wikipedia entry is also given in Frank Gill's Ornithology textbook. Frank's book has essentially cornered the market. He had experts in particular areas of ornithology review specific chapters. A similar description is given in the first volume of the magnificent Handbook of the Birds of the World, also cited at the end of the Wikipedia articles.
I would certainly not argue we have a complete understanding of the mechanics of powered flight at this point. However, when such understanding is achieved, Bernoulli's principle will have the major role in permitting powered flight in birds.
Best wishes,
Herb Wilson
Editor's Note: Here is a good review article on the Bernoulli effect and its contribution to flight. (www.aa.washington.edu/faculty/eberhardt/lift.htm)
From the boards ()
I am also convinced and outraged at the low quality of our high school textbooks, and as a high school teacher in Illinois District 214, I have twenty years of personal experience bolstering my outrage. However, Bill Bennetta's obvious contempt for teachers is unfortunate. Perhaps he does not realize how many of us struggle with this problem on a daily basis and agree with many of his points. Here is what my colleagues and I do in response to this problem: we do not use the textbooks. They sit on the shelves in our classrooms and gather dust. Or, better yet, my colleagues in the history department use the textbooks to show students how slanted particular views of history can be. The books are used as bad examples, giving students practice at critical thinking. High school students generally enjoy this sort of irreverence, making for lively classroom discussion.
In the English classroom (my own discipline) the problem is not that the textbooks contain faulty information, but that the textbook companies have gone out of their way to avoid offending anyone, which means they have to leave out any references to magic or religion, any comment that may be interpreted as sexist, agist or racist, any representation of a child eating junk food or showing disrepect to an elder, representations of young people watching too much television or indulging in hours of video game playing....and the list goes on. I once had a friend who worked for a textbook company. She showed me the list of taboo topics her editors forbade; it was ridiculous. The effort to offend no parent leads to vast, heavy compilations of innocuous and dull literature. So...my freshmen literature textbooks sit on the shelf in my classroom gathering dust. My students instead read paperback novels, short stories and plays that I pick out myself, or they read from photocopied material.
As for the bleak view that there is nothing anyone can do, this is untrue and self-defeating. I realize that some people may throw up their hands in despair if a phone call to the principal doesn't immediately lead to the dismissal of a textbook, but I can guarantee that principals keep track of these phone conversations, and when a textbook comes up for adoption, parent views are certainly considered. In fact, this is both a good and a bad thing. Fear of offending parents is part of the reason that administrators choose the bad (but seemingly safe) textbooks that we are all complaining about.
Ms. B
E-mail #4 ()
Wonderful show guys. It's nice to know you're out there
somewhere.
Firstly, I would love to hear a brief comment from each of your panelists (and yourself of course) as to which of the A-Z of pseudo-sciences they would most like to be true and why.(This is purely for fun.) This is a question which could also be put to many of your interviewee's for a good laugh.
Thanks again for your great efforts.
Leigh.
Name That Logical Fallacy ()
- Logical Fallacies
This statement is from the most recent e-mail from Neal Adams, in our ongoing debate regarding his 'expanding earth' claims.
'I do think the whole of the scientific community is wrong about the assembly of atoms. In fact I, for one have not heard a cogent theory about the assembly of atoms in my life, Except those general statements like Um .... 'In the massive furnaces of gigantic stars fusion processes this Hydrogen into the higher elements of the universe.'
They don't exactly say how. They just DO, and I should shut-up!'
Science or Fiction ()
Question #1: Cracking one's knuckles can cause arthritis later in life. Question #2: Sitting in a hot bath for an extended period of time can render a male temporarily infertile. Question #3: It is possible to contract the flu from the flu vaccine. Question #4: You should keep someone awake for 24 hours following a serious concussion.
Skeptical Puzzle ()
Last Week's puzzle:
If you are floating in a boat on a pond, and you are holding a 20lb cannon ball - if you drop the cannon ball overboard into the pond will the level of the pond rise, fall, or stay the same?
(Contributed by listener John Maddox)
Answer - the level of the pond will fall. The ball displaces its full weight in water when floating on the boat, but once in the pond it only displaces it's volume in water. Since it is denser than water, its weight in water is greater than its volume in water.
New Puzzle:
All the electricity was out in Aberdeen. None of the street lights or traffic signals had power. A dark limousine was cruising down the newly paved blacktop, with its headlights off. A young boy dressed totally in black (with no reflectors) stepped out to cross the street. The moon wasn't out and the boy had no flashlight, yet the driver stopped to let the boy cross the street. How did the driver see the boy?
S: The Skeptics' Guide to the Universe is produced by the New England Skeptical Society. For information on this and other podcasts, please visit our website at www.theskepticsguide.org. Please send us your questions, suggestions, and other feedback; you can use the "Contact Us" page on our website, or you can send us an email to info@theskepticsguide.org. 'Theorem' is produced by Kineto and is used with permission.
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