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Alan Turing using math to repair his bike

mathmutation.blogspot.com

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Re: Alan Turing using math to repair his bike

#51

Post by crispyambulance »

That's a charming story. It reminds me of skid-patch calculations on fixed gear bikes.

If you have ride a brakeless track bike and "stop" or slowdown the bike by skidding, there's certain gear ratios that you'll want to avoid. Basically, in skidding, you unweight the rear wheel by moving your body forward and lock the position of your cranks. The rear wheel will then skid and you can end up with a flat spot of wear on your tire (assuming your don't face-plant yourself when you do it wrong). The fewer the number of skid patches for your gear-ratio, the more rapid the wear-down on the tire will be.

There's even a calculator for this... https://www.bikecalc.com/skid_patch_calculator

If you're over 35, please, just use brakes and keep the track bike on the track! (stupid dangerous examples of skidding https://www.youtube.com/watch?v=W9xQcMniV84, don't do it).

Re: Alan Turing using math to repair his bike

#52

Post by geocrasher »

vcdimension wrote: post #47
loeg wrote: post #45

Earlier quoted context omitted.

(The web page hasn't been updated much for a while because Sheldon died several years ago.)

It's kept upto date by employees of the bike shop he worked for (Harris Cyclery), his widow, and his friend John Harris (a nationally recognized bicycle expert). The most recent post was about 3 weeks ago: https://sheldonbrown.com/blog/

I am absolutely delighted to see Sheldon Brown's website posted on HN! It is an incredible resource.

Re: Alan Turing using math to repair his bike

#53

Post by phaedrus »

matthewmcg wrote: post #3

This anecdote is memorably presented as an application of modular arithmetic (along with the behavior of Enigma machine rotors) in Neal Stephenson’s Cryptonomicon . See the discussion in this review of the book: https://www.ams.org/notices/199911/rev-kasman.pdf

Your mention of modular arithmetic makes me draw a connection between this story and the way I think about ceiling fan pull chains.

Suppose the fan is clearly starting on high and you want to turn it off, but you don't know if the order of settings is "high-low-off", or "high-medium-low-off" (three states or four).

It's often difficult to tell if the fan is coasting off or just spinning down to low. If you get it wrong and pull one time too many, it goes back to high and you have to start over.

Therefore I always pull fan chains eleven (11) times to turn them off, so that I don't have to know if it's a three or four state fan. (Also works for on-off pull chains.) Pulling the chain 59 times would extend this technique to cover five-state fans, but I've never encountered one.

Re: Alan Turing using math to repair his bike

#54

Post by vcdimension »

donquichotte wrote: post #34

I guess if you have a hammer, everything looks like a nail, even if you are Alan Turing! Tangentially related, I have recently become aware of a sound similar to a bag of potato chips being crushed coming from the rear wheel of my mountain bike. Closer inspection showed that the rear wheel hub exhibited an unwanted additional degree of freedom with respect to the rest of the wheel. The hub was able to be moved slight…

You could make some of the money back from those tools, and help others in a similar situation, by renting them out on https://fatllama.com (or some other sharing website/app such as https://olioex.com/). Sharing & hiring saves money and environmental impact.

Re: Alan Turing using math to repair his bike

#55

Post by gmac »

ihaveajob wrote: post #25
avg_dev wrote: post #15

Earlier quoted context omitted.

I didn't know about the gas masks being ubiquitous during the war; that makes that part a little less surprising. History can be sad.

I bought one at a swap meet in Amsterdam a few years ago. They were piled up high and cheap. It made a fun gift for a friend back home, but we got really odd looks on the train when wearing it :).

Ah, careful: https://www.nationalasbestos.co.uk/news/wwii-gas-masks-a-lif...

Re: Alan Turing using math to repair his bike

#56

Post by loeg »

vcdimension wrote: post #47
loeg wrote: post #45

Earlier quoted context omitted.

(The web page hasn't been updated much for a while because Sheldon died several years ago.)

It's kept upto date by employees of the bike shop he worked for (Harris Cyclery), his widow, and his friend John Harris (a nationally recognized bicycle expert). The most recent post was about 3 weeks ago: https://sheldonbrown.com/blog/

Yeah, that's why I qualified it with "much." Trying to provide some context for HN readers unfamiliar with Sheldon.

Re: Alan Turing using math to repair his bike

#58

Post by Arrath »

phaedrus wrote: post #53
matthewmcg wrote: post #3

This anecdote is memorably presented as an application of modular arithmetic (along with the behavior of Enigma machine rotors) in Neal Stephenson’s Cryptonomicon . See the discussion in this review of the book: https://www.ams.org/notices/199911/rev-kasman.pdf

Your mention of modular arithmetic makes me draw a connection between this story and the way I think about ceiling fan pull chains. Suppose the fan is clearly starting on high and you want to turn it off, but you don't know if the order of settings is "high-low-off", or "high-medium-low-off" (three states or four). It's often difficult to tell if the fan is coasting off or just spinning down to low. If you get it wro…

...huh. Well, I am going to try this.

Re: Alan Turing using math to repair his bike

#59

Post by phiiiillll »

crispyambulance wrote: post #51

That's a charming story. It reminds me of skid-patch calculations on fixed gear bikes. If you have ride a brakeless track bike and "stop" or slowdown the bike by skidding, there's certain gear ratios that you'll want to avoid. Basically, in skidding, you unweight the rear wheel by moving your body forward and lock the position of your cranks. The rear wheel will then skid and you can end up with a flat spot of wear o…

That's funny, I'm 41 and planning on setting up my brakeless track bike for the road again this afternoon (changing the gearing to 42-17 and switching from drops to a wide riser bar). If it goes badly I'll think of your warning.
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