I really like this one, but got to warn you. This guy Feynman was a regular joker.
His mind works just like mine (only, I'm not much of a physics professor), so he hadn't me fooled for a second. Well, maybe he had? What do I know!
The solution to his little problem, stated in his own words below, is really very simple.
It's safe to tell you this, because either he will mix you up completely and have you arrive at the wrong conclusion,
or you will see it in a flash—it can't be helped.
| Surely You're Joking, Mr. Feynman! by Richard P. Feynman, 1985 |
| I once did an experiment in the cyclotron laboratory at Princeton that had some startling results. There was a problem in a hydrodynamics book that was being discussed by all the physics students. The problem is this: You have an S-shaped lawn sprinkler—an S-shaped pipe on a pivot—and the water squirts out at right angles to the axis and makes it spin in a certain direction. Everybody knows which way it goes around; it backs away from the outgoing water. Now the question is this: If you had a lake, or swimming pool—a big supply of water—and you put the sprinkler completely under water, and sucked the water in, instead of squirting it out, which way would it turn? Would it turn the same way as it does when you squirt water out into the air, or would it turn the other way? The answer is perfectly clear at first sight. The trouble was, some guy would think it was perfectly clear one way, and another guy would think it was perfectly clear the other way. So everybody was discussing it. I remember at one particular seminar, or tea, somebody went up to Prof. John Wheeler and said, Which way do you think it goes around? Wheeler said, Yesterday, Feynman convinced me that it goes around backwards. Today, he's convinced me equally well that it goes around the other way. I don't know what he'll convince me of tomorrow! I'll tell you an argument that will make you think it's one way and another argument that will make you think it's the other way, OK? One argument is that when you're sucking water in, you're sort of pulling the water with the nozzle, so it will go forward towards the incoming water. But then another guy comes along and says, Suppose we hold it still and ask what kind of a torque we need to hold it still. In the case of the water going out, we all know you have to hold it on the outside of the curve, because of the centrifugal force of the water going around the curve. Now, when the water goes around the same curve the other way, it still makes the same centrifugal force toward the outside of the curve. Therefore the two cases are the same, and the sprinkler will go around the same way, whether you're squirting water out or sucking it in. (pp 63-64) |
Feynman never gives the solution, so I won't, either. Anyway, maybe I'm wrong, after all!
But you can read about the startling results here.
It's a tie?
Feynman was notorious for opening, not cracking (which may be the same thing, anyway), all the safes in Los Alamos. Likewise, in the Dutch Army (such as it is) some fellow sergeants once tied me up, or down, on my bed and went off to have a couple of beers in the mess. Somebody try to pull a stunt like tying me up now, with all my claustrophobia, I'm gonna *u**ing kill him. To be sure, and to their amazement, I walked in some fifteen minutes later, having shed my shackles like Houdini (who spelled his first name different from mine or he'd really have made it). Admittedly, those guys hadn't done a very good job when tying me up. But neither had those scientists at Los Alamos when locking up their safes with State Top Nuclear Secrets in them.
Feynman's Chimes Anytimes
The story of the clocks; how both Feynman and I made an art and a science of counting time in your head.
While he was a very good drummer, or so he tells you, I am better at keeping time—or so I'll tell you.
Richard P. Feynman books
All written straight to my heart—and, if you're lucky, yours
Surely You're Joking, Mr. Feynman!
The Pleasure of Finding Things Out
What Do You Care What Other People Think?:
Further Adventures of a Curious Character
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