Old puzzle

I found an old (early 70s) puzzle book that contained the following problem:

"A bicycle is supported on level ground such that it can't fall over
sideways. The pedal cranks are orientated vertically. A string is tied
to the bottom crank and pulled gently backwards. Does the bike move
backwards or forwards?"

The answer, as given, was "backwards", with some brief cod-science about
the string "unable to overcome the force of the gears", but it got me
thinking. With today's modern low gearings for those dark side
machines and some mountain bikes, is it possible to have a similar
situation whereby a constant rearward pull on the string caused the bike
to the bike moves forwards?

R.

Richard wrote:

With today's modern low gearings for those dark side
machines and some mountain bikes, is it possible to have a similar
situation whereby a constant rearward pull on the string caused the bike
to the bike moves forwards?

At first thought, you'd need a *really* low gear. Intuitively, it would
seem that it's distance rather than ratio that counts - so you'd need a
gear that causes more linear movement in the pedal than in the bike.

So a sub 1:1 rotation ratio won't necessarily cut it: you'd need an
additional scaling related to your pedal circle diameter and wheel size.

I supply no evidence for that...

--
Mark.
http://tranchant.plus.com/

On 06/08/2005 11:09:00 Richard .address.uk wrote:

I found an old (early 70s) puzzle book that contained the following
problem:

"A bicycle is supported on level ground such that it can't fall over
sideways. The pedal cranks are orientated vertically. A string is tied
to the bottom crank and pulled gently backwards. Does the bike move
backwards or forwards?"

The answer, as given, was "backwards", with some brief cod-science about
the string "unable to overcome the force of the gears", but it got me
thinking. With today's modern low gearings for those dark side machines
and some mountain bikes, is it possible to have a similar situation
whereby a constant rearward pull on the string caused the bike to the bike
moves forwards?

Only to the point of the pedal being horizontal. I have just tried in on the trike, and it moved forward.

--
Buck

I would rather be out on my Catrike

www.catrike.co.uk

Buck wrote:

The answer, as given, was "backwards", with some brief cod-science about
the string "unable to overcome the force of the gears", but it got me
thinking. With today's modern low gearings for those dark side machines
and some mountain bikes, is it possible to have a similar situation
whereby a constant rearward pull on the string caused the bike to the bike
moves forwards?


Only to the point of the pedal being horizontal. I have just tried in on the trike, and it moved forward.

Well, yes, I figured only to the point of horizontality.

Thanks for the evidence at first hand, not having a ludicrously
low-geared machine myself. But, what's this? ...empirical evidence?
It'll never do, not in this newsgroup ;-)

R.

On 06/08/2005 11:42:50 Richard .address.uk wrote:

Buck wrote:

The answer, as given, was "backwards", with some brief cod-science about
the string "unable to overcome the force of the gears", but it got me
thinking. With today's modern low gearings for those dark side machines
and some mountain bikes, is it possible to have a similar situation
whereby a constant rearward pull on the string caused the bike to the
bike moves forwards?

Only to the point of the pedal being horizontal. I have just tried in on
the trike, and it moved forward.

Well, yes, I figured only to the point of horizontality.

Thanks for the evidence at first hand, not having a ludicrously low-geared
machine myself. But, what's this? ...empirical evidence? It'll never do,
not in this newsgroup ;-)

I'm sure someone will argue against me, don't worry.

The gearing on the trike by the way, front chainring, 27 tooth, rear sprocket 34 tooth, wheel size 406, I think that is about 15" per revolution.

--
Buck

I would rather be out on my Catrike

http://www.catrike.co.uk

Richard .address.uk writes:

Well, yes, I figured only to the point of horizontality.

Not even to the point of horizontality. Only while the backward
movement of the pedal (where the string is attached) relative to
the bike is greater than the consequent movement forward of the
bike relative to the ground. That is, it moves forward only while
the point where the string is attached is moving towards you. While
you *might* be able to stand on a spoke, you can't push with this
taut string.

Brendan
--
Brendan Halpin, Department of Sociology, University of Limerick, Ireland
Tel: w +353-61-213147 f +353-61-202569 h +353-61-338562; Room F2-025 x 3147
http://www.ul.ie/sociology/brendan.halpin.html

Buck wrote:

The gearing on the trike by the way, front chainring, 27 tooth, rear
sprocket 34 tooth, wheel size 406, I think that is about 15" per
revolution.

Tsk! /Way/ overgeared...

--
Dave Larrington - http://www.legslarry.beerdrinkers.co.uk/
24/34 - 406

On Wed, 08 Jun 2005 11:03:27 GMT, Buck wrote:


On 06/08/2005 11:42:50 Richard .address.uk wrote:

Buck wrote:

The answer, as given, was "backwards", with some brief cod-science about
the string "unable to overcome the force of the gears", but it got me
thinking. With today's modern low gearings for those dark side machines
and some mountain bikes, is it possible to have a similar situation
whereby a constant rearward pull on the string caused the bike to the
bike moves forwards?

Only to the point of the pedal being horizontal. I have just tried in on
the trike, and it moved forward.

Well, yes, I figured only to the point of horizontality.

Thanks for the evidence at first hand, not having a ludicrously low-geared
machine myself. But, what's this? ...empirical evidence? It'll never do,
not in this newsgroup ;-)

I'm sure someone will argue against me, don't worry.

No they wont!


--
Trevor Barton

On 06/08/2005 12:10:42 "Dave Larrington" wrote:

Buck wrote:

The gearing on the trike by the way, front chainring, 27 tooth, rear
sprocket 34 tooth, wheel size 406, I think that is about 15" per
revolution.

Tsk! /Way/ overgeared...

The speed scares me.

--
Buck

I would rather be out on my Catrike

http://www.catrike.co.uk