Brain Teasers from Richard Feynman

[pokerfan]

http://varatek.com/scott/feynman_problems.html

[pokerfan]

1. kick - anyone??? Bueller? Bueller?

I had to cheat and look up the choo-choo answer. The solution to the fourth question was beat into my head thirty years ago as an undergrad EE major so it's a little arcane and not what I would consider a brain teaser.

[Drum]

2. I like.

:)

[pokerfan]

3. You must show your work

[EstimatedProphet]

4. Why aren't there any answers listed?

How do I know if I've gotten them right?

[trof]

5. What keeps a train on the track?

Damn. I always thought it was the wheel flanges.
According to Wiki:
The rails are inclined slightly towards each other, typically on a slope of 1 in 20. This combined with coning of the wheels helps guide rail vehicles along the track. It is this rather than the wheel flange that keeps the vehicles from derailing. The flange is only a safety device that operates as a last resort or in cases where a vehicle is traveling very slowly on heavily curved track (when you will hear a metallic screeching noise caused by the flange/rail contact).
http://simple.wikipedia.org/wiki/Railroad

[mainegreen]

6. I like it.

The mirror one is good. Nicely worded problem that cleverly tries to get you to think of it wrong.
"up. But it's not top-to-bottom mixed up, because the top of the head of the image is there at the top, and the feet are down at the bottom. The question is: how does the mirror know to get the left and right mixed up, but not the up and down?"

Of course fully written out: "the head is at the top, the feet are at the bottom, the right is on the right and the left is on the left" and you realize the mirror is not doing what the problem seems to state it is. Clever.

Train Problem: Gravity is what they are looking for?

Sprinkler: Hmmm. On the surface you would think it would spin the other way, but I sense a trap....

EM Paradox: Ung, saving that one for later.

Fun, thanks!

[pokerfan]

7. trof found the answer to the train

I thought it was the flanges too. I found the original patent and discovered that there's an entire science invovled in finding the optimum geometry involved. Such an elegant solution. Uf the train starts to drift to say the left, the geometry forces that wheel to essentially get larger while the right gets smaller. The "larger wheel is now covering more distance than the "smaller" wheel and since the axel has a pivot, the train steers itself back to the center. This phenomenon is called hunting and the train is doing it constantly and it's what creates the gentle side to side rocking.

The sprinkler problem: Key word is "s-shaped." think about what the water molecules are doing as they round the bend.

[pokerfan]

8. Answers

The sprinker:
http://web.mit.edu/Edgerton/www/FeynmanSprinkler.html
http://en.wikipedia.org/wiki/Feynman_sprinkler

The EM paradox:
http://www.maxwellsociety.net/PhysicsCorner/Miscellaneous%20Topics/FeynmanParadox.html