Law of Gravitation - An Example of Physical Law
The Relation of Mathematics and Physics
The Great Conservation Principles
Symmetry in Physical Law
The Distinction of Past and Future
Probability and Uncertainty - The Quantum Mechanical View of Nature
Seeking New Laws
The same thing happened: something would look good at first and then turn out to be horrifying. For example, there was a book that started out with four pictures: first there was a windup toy; then there was an automobile; then there was a boy riding a bicycle; then there was something else. And underneath each picture it said, “What makes it go?”
I thought, “I know what it is: They’re going to talk about mechanics, how the springs work inside the toy; about chemistry, how the engine of the automobile works; and biology, about how the muscles work.”
It was the kind of thing my father would have talked about: “What makes it go? Everything goes because the sun is shining.” And then we would have fun discussing it:
“No, the toy goes because the spring is wound up,” I would say. “How did the spring get wound up?” he would ask.
“I wound it up.”
“And how did you get moving?”
“From eating.”
“And food grows only because the sun is shining. So it’s because the sun is shining that all these things are moving.” That would get the concept across that motion is simply the transformation of the sun’s power.
A series of four lectures on physics, specifically quantum electrodynamics, by Richard Feynman. Only Part 1 is available on Google Video and the rest are in streaming Real format (blech)…hopefully they too will make their way onto Google Video.
Update: I got an email from the nice folks at Vega Science Trust asking me to change the wording of this entry with regard to encouraging people to put these copyrighted videos up on Google Video. Fair enough…what I really meant by that is I wish the videos were presented in a more useable manner than RealVideo format. If there’s one thing that YouTube has shown us more than anything, it’s that people find watching video in embedded Flash players really convenient.
Cadaeic Cadenza is a 3834-word story by Mike Keith where each word in sequence has the same number of letters as the corresponding digit in pi. (thx, mark, who has more info on constrained writing) Related: The Feynman point is the sequence of six 9s which begins 762 digits into pi. “[Feynman] once stated during a lecture he would like to memorize the digits of pi until that point, so he could recite them and quip ‘nine nine nine nine nine nine and so on.’”
Here’s the original problem essentially as it was posed to us: “A plane is standing on a runway that can move (some sort of band conveyer). The plane moves in one direction, while the conveyer moves in the opposite direction. This conveyer has a control system that tracks the plane speed and tunes the speed of the conveyer to be exactly the same (but in the opposite direction). Can the plane take off?”
I’ll give you a few moments to think about that before discussing the answer…
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Cecil says that the obvious answer — that the plane does not take off because it remains stationary relative to the ground and the air — is wrong. The plane, he says, can take off:
But of course cars and planes don’t work the same way. A car’s wheels are its means of propulsion—they push the road backwards (relatively speaking), and the car moves forward. In contrast, a plane’s wheels aren’t motorized; their purpose is to reduce friction during takeoff (and add it, by braking, when landing). What gets a plane moving are its propellers or jet turbines, which shove the air backward and thereby impel the plane forward. What the wheels, conveyor belt, etc, are up to is largely irrelevant. Let me repeat: Once the pilot fires up the engines, the plane moves forward at pretty much the usual speed relative to the ground—and more importantly the air—regardless of how fast the conveyor belt is moving backward. This generates lift on the wings, and the plane takes off. All the conveyor belt does is, as you correctly conclude, make the plane’s wheels spin madly.
After reading the question this morning and discussing it with Meg for, oh, about 3 hours on and off, I was convinced that Cecil was wrong. There’s no way that plane could take off. The conveyor belt keeps pace with the speed of the plane, which means the plane remains stationary from the POV of an observer on the ground, and therefore cannot lift off.
Then I read Cecil’s answer again this evening and I’ve changed my mind; I’m fairly certain he’s right. For a sufficiently long conveyor belt, that plane is taking off. It doesn’t matter what the conveyor belt is doing because the airplane’s energy is acting on the air, not the belt. I had better luck simplifying the problem like so: imagine instead of a plane, you’ve got a rocket with wheels sitting on that belt. When that rocket fires, it’s eventually going to rocket off the end of that belt…which means that it doesn’t remain stationary to the ground and if it had wings, it would fly.
Update: Well, that got out of control in a hurry…almost 300 comments in about 16 hours. I had to delete a bunch of trolling comments and it’s not productive to keep going, so I closed it. Thanks for the, er, discussion and remember, the plane takes off. :)
When bent, why does dry spaghetti break into three or more pieces instead of two? This was one of the simple problems Richard Feynman amused himself with but never solved. Someone’s come up with the answer: when the first breakage occurs, it causes a local increase in the curvature of the two pieces, resulting in more breakage. (thx dj)
It made Feynman think wistfully about the days before the future of science had begun to feel like his mission — the days before physicists changed the universe and became the most potent political force within American science, before institutions with fast-expanding budgets began chasing nuclear physicists like Hollywood stars. He remembered when physics was a game, when he could look at the graceful narrowing curve in three dimensions that water makes as it streams from a tap, and he could take the time to understand why.
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