bike puzzle(s)

Anyone interested in puzzles? Do you have any bike puzzles to share?

Here is one I saw in a book*. You can actually try this if you have a fixed gear at your disposal.

Below is a regular fixed gear bike. As you can see(!?), a lose yellow rope is resting on the floor where one end is tied to the left pedal spindle.

If someone was to kneel in front of the bike and pull the rope, will the crank move clockwise, counter clockwise, or not at all ?

You can assume a magic force is keeping the bike upright and front tire pointing straight. Oh, and assume the wheels do have spokes although it looks otherwise.

* Mathematical Carnival by M. Gardner

original bike photo from: http://fixedgearsclub.blogspot.com/2011/04/why-have-fixed-gear-bike...

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Replies to This Discussion

Permalink Reply by Zoetrope on January 7, 2012 at 9:22am

Haha. Uhhh, the crank would move counter clockwise a little bit, but not much.

**Waits to see how wrong I am**

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Permalink Reply by Ken Gray on January 7, 2012 at 1:34pm

+1. Could it be that simple?

Brendan said:

Haha. Uhhh, the crank would move counter clockwise a little bit, but not much.

**Waits to see how wrong I am**

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Permalink Reply by Doug Haynes on January 7, 2012 at 3:56pm

It all depends on if the rear wheel is able to spin freely...

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Permalink Reply by Duppie on January 7, 2012 at 4:22pm

Correct. If it is a fixed gear, nothing will move. As soon as the rope is taut and the crank starts to move forward, the wheel and bike will start to move backward.

notoriousDUG said:

It all depends on if the rear wheel is able to spin freely...

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Permalink Reply by Adam "Cezar" Jenkins on January 7, 2012 at 4:33pm

You're missing an important assumption. That the back wheel cannot slide. That's most likely to happen, pull and slide.

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Permalink Reply by Duppie on January 7, 2012 at 4:39pm

Yeah, and let us not forget about the amount of chain slack the average fixie has either;)

Adam "Cezar" Jenkins said:

You're missing an important assumption. That the back wheel cannot slide. That's most likely to happen, pull and slide.

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Permalink Reply by ilter on January 7, 2012 at 7:02pm

Wow, so many replies :)

You folks are thorough. Let`s see if I can address some of these issues.

Bike is a regular fixed gear, as mentioned earlier. You should also assume that the bike is heavy enough that the tires will not slide. In other words, if the bike is moving, the tires are rotating, so is the crank.

I think the chain can have some slack. However it will make things less complicated if you assume it does not have any slack (let`s say it has one of those nice tensioners in rear dropouts :) ).