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"James Hodson" wrote in message

Don't bicycles stay upright because of the gyroscopic action on their
wheels. (Yes, I know that's extremly badly put.) Calling all
physicists.

Nope, not gyroscopes, more like hockey sticks or golf clubs - balancing one
of these on the palm of your hand is the same problem as balancing a bike.

's an FAQ too...

cheers,
clive

In message , James Hodson
writes
On Tue, 5 Aug 2003 19:30:28 +0100, "Clive George"
wrote:
"James Hodson" wrote in message

Don't bicycles stay upright because of the gyroscopic action on their
wheels. (Yes, I know that's extremly badly put.) Calling all
physicists.

Nope, not gyroscopes, more like hockey sticks or golf clubs - balancing one
of these on the palm of your hand is the same problem as balancing a bike.

OK, Clive. Next question: Why is balancing easier on a moving bike
than on a stationary, track-standing one?

You balance a moving bike by steering it - first you go over a bit one
way, then over a bit the other way, etc. You can't do that when
stationary.

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"James Hodson" wrote in message
...
On Tue, 5 Aug 2003 19:30:28 +0100, "Clive George"
wrote:

"James Hodson" wrote in message

Don't bicycles stay upright because of the gyroscopic action on their
wheels. (Yes, I know that's extremly badly put.) Calling all
physicists.

Nope, not gyroscopes, more like hockey sticks or golf clubs - balancing
one
of these on the palm of your hand is the same problem as balancing a
bike.


OK, Clive. Next question: Why is balancing easier on a moving bike
than on a stationary, track-standing one?

How do you hold the hockey stick up? By moving your hand around underneath
it to catch the fall.
If you're stationary on a bike you can't do this. If you're moving you steer
so the bottom of the bike moves underneath you to catch the fall.

cheers,
clive

"James Hodson" wrote in message
...
The BBC site states: "... the Segway uses gyroscopes to stay upright."
Don't bicycles stay upright because of the gyroscopic action on their
wheels. (Yes, I know that's extremly badly put.) Calling all
physicists.

I'm not a physicist. But I do know that the stability of bicycles is
nothing (well, almost nothing) to do with gyroscopic action, unless you have
extremely massive or fast spinning wheels - neither of which are common on
bicycles.
It's all to do with the geometry of the front forks.
A chap called David E.H. Jones published a paper about it in 1970, which can
be found in PDF format he
http://ist-socrates.berkeley.edu/~fa...onesBikeBW.pdf
It tells you everything you probably need to know about the subject.

Andrew.

On Tue, 5 Aug 2003 19:51:50 +0100, "Clive George"
wrote:

How do you hold the hockey stick up? By moving your hand around underneath
it to catch the fall.
If you're stationary on a bike you can't do this. If you're moving you steer
so the bottom of the bike moves underneath you to catch the fall.


OK guys. I have the idea now. Thanks.

James

--
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In ,
James Hodson typed:

The BBC site states: "... the Segway uses gyroscopes to stay upright."
Don't bicycles stay upright because of the gyroscopic action on their
wheels. (Yes, I know that's extremly badly put.) Calling all
physicists.


that entered poular mythology many years ago but was disproved by a simple
experiment of setting up a slightly smaller wheel which counter rotated at
the same speed as the bike wheel ie giving equal and oposite angular
momentum along the wheel axis. Balance and steering were unchanged.

a less rigourous dis-proof is to consider slow speed balance when any gyro
scopic effect is minimal.

Sterring and balance have more to do with bike geometry esp the "trail"
(horizontal distance between stering axis and point of contact of the front
wheel with the ground.

p - ex physicist - k

Clive George must be edykated coz e writed:

"James Hodson" wrote in message
...
On Tue, 5 Aug 2003 19:30:28 +0100, "Clive George"
wrote:

"James Hodson" wrote in message

Don't bicycles stay upright because of the gyroscopic action on their
wheels. (Yes, I know that's extremly badly put.) Calling all
physicists.

Nope, not gyroscopes, more like hockey sticks or golf clubs - balancing
one
of these on the palm of your hand is the same problem as balancing a
bike.


OK, Clive. Next question: Why is balancing easier on a moving bike
than on a stationary, track-standing one?

How do you hold the hockey stick up? By moving your hand around underneath
it to catch the fall.
If you're stationary on a bike you can't do this. If you're moving you steer
so the bottom of the bike moves underneath you to catch the fall.

cheers,
clive

Gyroscopic effect does come into play, more so as you move faster, the
specific mass of the wheels increase due to velocity, and the centripedal
force generated within the wheels mass area becomes more difficult to
deflect off line, but at slower speeds the bicycle is balanced by the rider
shifting weight about, usually without thinking about it, both by moving the
body and by altering the steering, so all answers are correct.

Ian

On Tue, 5 Aug 2003 19:28:49 +0000 (UTC), "Paul Kelly"
wrote:

p - ex physicist - k


OK. Thanks Paul et al. I'm convinced.

James

--
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On Tue, 5 Aug 2003 19:28:49 +0000 (UTC), "Paul Kelly"
wrote:

Sterring and balance have more to do with bike geometry esp the "trail"
(horizontal distance between stering axis and point of contact of the front
wheel with the ground.

My 8 year old has one of those micro scooters. The "fork" is a simple
folded bracket and is near (but not quite) symmetrical. The bars/fork
can rotate in a complete 360°.

His mum (we're divorced and live quite a distance apart) isn't a
cyclist and doesn't appreciate such things. So neither of them had
ever noticed that with the bars one way round the thing is completely
unstable (I can barely stay on at walking pace), yet spin the bars
through 180° and it's easy to ride. The trail in this fork can't be
more than 1/2", yet it's enough to totally transform the handling.

Some marker pen work on labelling the bars made future riding a bit
more predictable.