Dot Physics has been assimilated by the Borg, but (unsurprisingly) Rhett, through his blood, sweat and tears, continues to post cool stuff. This time, it’s an angular momentum demo and explanation. I’ll post the video here as a teaser; go to the post for the explanation
I agree with a couple of commenters there — I also like the demonstration where you spin the wheel and sit on a rotatable stool, and then reorient the wheel.
What’s a Lagrangian? and something you can do with it: Harmonic Oscillator #2 – Lagrangian Formulation, at Built on Facts.
So why all that extra trouble? In this case, just to see how things work. But in other cases, this is our only option. There are plenty of times (for instance, a roller coaster on tracks) where the forces involved (such as the tracks on the car) are so blisteringly complicated as to be practically impossible to solve. However, it’s easy to write the relation between the track height and the potential energy, and the Lagrangian formulation can automatically give us a much simpler differential equation to solve.
After months of tinkering, I have discovered the best and easiest way to restore dry Play-Doh to its perfect state (besides Hasbro’s former suggestion that you buy a new can).
Several decades too late to help me, which I assume is everybody’s first concern, but good to know nonetheless. Tinkering to systematically find the best method. That’s science, baby!
The Big Picture: 100 days in Glacier National Park is a collection culled from the blog/journal of the same name. The Big Picture has bigger pictures (imagine that) but the journal has more annotations.
Why triangular snowflakes grow
While most snowflakes are hexagonal, triangular forms have long been observed. When Libbrecht and Arnold grew snow crystals in the lab they found far more triangular forms than would be expected from mere random growth perturbations.
Air moving past a falling crystal will increase its growth, they note. A tiny factor – perhaps a piece of dust on the crystal – that causes a small change in growth of a perfect hexagon will also tilt the crystal, changing the way air moves past the crystal and – in their model – increasing the way the crystal grows at certain points and inducing a more triangular appearance.
Also: Unusual Snow Crystals. Be sure to check out the photo galleries.
Update: and The Unbelievable World of Snowflakes
Letters of Note: “He is a second Dirac, only this time human.”
Robert Oppenheimer’s letter of recommendation on behalf of Richard Feynman.
The reason for telling you about him now is that his excellence is so well known, both at Princeton where he worked before he came here, and to a not inconsiderable number of “big shots” on this project, that he has already been offered a position for the post war period, and will most certainly be offered others. I feel that he would be a great strength for our department, tending to tie together its teaching, its research and its experimental and theoretical aspects. I may give you two quotations from men with whom he has worked. Bethe has said that he would rather lose any two other men than Feyman from this present job, and Wigner said, “He is a second Dirac, only this time human.”
Archive of Bart Simpson’s Blackboard Writings
I had no idea that I could have let the proverbial cat out of the bag when I linked to different ways of lacing/tying your shoes. But it turns out that the CIA used lacing patterns as ways to send messages (slideshow). It’s the visual part of Tinker, tailor, soldier… illusionist?
“The instant the performer sees the spectator take a cigarette, cigar, or pipe, he takes the packet of matches from his pocket, tears off one match, and holds packet and match ready to ignite the match,” the magician John Mulholland wrote in a manual in the 1950s. “He does these things openly because what he does can only be looked upon as a friendly and courteous gesture.”
Mulholland’s instructions were written not for stage magicians, but for the covert operatives of the CIA. At the height of the Cold War – in the era of nuclear missiles and submarines, amid the tangled cloak-and-dagger maneuverings of espionage and counterespionage – the agency was also secretly doing something else. It was trying to learn to do magic.
Fortunately it’s all been declassified. Whew!
Catching up with blogs after Thanksgiving travel. I saw this on Chad’s linked list. Zen Moments: My Favorite Liar
What made Dr. K memorable was a gimmick he employed that began with his introduction at the beginning of his first class:
“Now I know some of you have already heard of me, but for the benefit of those who are unfamiliar, let me explain how I teach. Between today until the class right before finals, it is my intention to work into each of my lectures … one lie. Your job, as students, among other things, is to try and catch me in the Lie of the Day.”
And thus began our ten-week course.
I think that’s a pretty interesting way to engage the students.
Later on, the author lists some lessons learned from the exercise, including
“Experts” can be wrong, and say things that sound right – so build a habit of evaluating new information and check it against things you already accept as fact.
It should probably go without saying, but this holds true for nonexperts, only moreso. Skepticism is a tool that gets refined as one progresses in science, and one tends to develop a decent BS detector. For claims that jibe with what I already know, provisional acceptance is easier. If an assertion seems dubious, I require more convincing. I like Feynman’s trick (can I use that word, in light of the recent kerfuffle?) which he explains in one of his books, of thinking of an object or scenario, trying to disprove an assertion.