Circus acts

[Johnny Two Peda]

Peter <[email protected]> wrote in message news:<[email protected]>...
> epicyclist wrote:
> > Peter wrote:
> >
> >> epicyclist wrote:
> >>
> >>> As I watch my little boy fight his bicycle and fall off in his transition from stabilisers to
> >>> free cycling I think "Gyroscopes". Yet many still say that balancing on a bike is a circus act
> >>> of steering correction. I can see that this effect becomes significant below 2mph just before
> >>> you fall off due to lack of forward velocity but why does the myth still prevail?
> >>
> >>
> >>
> >> Possibly because experiments have been done with counter-rotating wheels mounted on the bicycle
> >> to cancel gyroscopic effects. The bike still rides and steers about the same although I believe
> >> it did fall over faster when it was pushed and let go without a rider. Various modifications of
> >> the steering geometry were also tried and described in an article in "Physics Today" [wrong
> >> date].
> >>
> >>
> > Yes, they would not have made the grade for GCSE though would they?
>
> I suggest you read the article - the correct reference is David Jones, "Physics Today," April,
> 1970, pp34-40. The conclusion is that the bicycle has substantial inherent stability due to the
> steering geometry
> - so it is neither the result of gyroscopic forces nor a circus balancing act.

<<<< S N I P >>>>

An interesting example of this would be a carny trick I saw at the Big E last autumn. The huckster
had a fairly normal looking BMX bike, the con was to ride the bike in a straight line for about 15
feet (at $2.00 a pop). Obviously, the huckster had no problems making the course, but each and every
rube fell flat on their face. After quite a few chagrined customers had hit the dirt, I noticed the
headset looked a bit odd, the headtube seemed to be twice the normal diameter. The bike was rigged
with mechanism that reversed the fork travel in relation to the bar travel....ie. turn the bar left,
the fork goes right! As each rider attemped to correct a steering error (negative feedback) the
mechanism would compound the error (positive feedback). The speeds were slow enough to negate any
gyroscpic effect....this was pure steering. Two rubes were successful in the 15-20 minutes I
watched, each used a different method to overcome the con....the first ( wearing a faded Colnago tee
shirt ) pushed off fast with his arms folded across his chest, steering with no hands ... the second
woman crossed her arms on the bars ... left hand on right grip etc.

Oddly, even after being shown how to beat the con, the rubes kept paing $2.00 to perform a face
plant.....I guess that discussion belongs in one of the Psych groups!

I've gotta go find the Physics Today article....sounds interesting..

 

[Jasper Janssen]

On Tue, 03 Jun 2003 08:06:51 +0200, Michel Schinz <[email protected]> wrote:

>There are also many experiments that one could do to check whether gyroscopic forces really
>matter. For example, you could try to modify your bike to lock the steering. If you are right,
>such a bike should be ridable on a straight descent, provided you use your feet to keep balance at
>very low speed.

Are you trying to 'improve the gene pool', as it were, from people who believe gyroscopy?

Jasper

 

[Andy Dingley]

On Mon, 02 Jun 2003 18:32:58 +0100, "Kit Wolf" <[email protected]> wrote:

>My physicist flatmate swears he saw an educational video where a cyclist rode a bike with a fixed
>speed flywheel attached. When he accelerated to the correct speed, the flywheel and bicycle wheel
>gyroscopic forces exactly counteracted each other and he fell off.

Who made it ? Eric Laithwaite ?

 

[Chris Zacho "Th]

Ever see a rider do a track stand? No gyroscopes there.

Most of the job is micro steering, but there are many other factors involved, including gyroscopic.
However, it's contribution to keeping a bicycle upright is, I believe, minimal at best. The child
you are watching, remember, has not yet aquired this delicate skill, so he is relying heavilly on
these other factors. Which is why he tetters so much.

When you consider the insignificant weight of a wheel, when compared to the total mass of both
bike and rider, you will realise the wheels would have to be spinning at several hundred
(thousand?) revolutions a minute to provide enough gyroscopic force to maintain the bicycle in an
upright position.

I'm sure Jobst or Sheldon have a more detailed and scientific answer.

Guys?

May you have the wind at your back. And a really low gear for the hills! Chris

Chris'Z Corner "The Website for the Common Bicyclist": http://www.geocities.com/czcorner