Re: Fell off

Simon Brooke

in message <321gopF3hf77mU1@individual.net>, James Annan
('still_the_same_me@hotmail.com') wrote:

> Your logic is broken, I'll merely point out that the countersteering
> is NOT "in effect a short turn in the other direction", it is in fact
> a loss of balance in which the _bicycle_ (contact patch) moves to one
> side while the _rider_ is left behind. If you did it for more than a
> brief moment, you would fall off, not turn.

I suggest you try riding a bicycle. You will find that if you lean the
bicycle to one side, it will turn to that side, without any need for
any other steering input. If you lean your body to one side, thus
moving your centre of gravity, then the bike will naturally lean to the
other side, and thus you can easily initiate a turn in either
direction. You can demonstrate this easily by holding the bike by the
back of the saddle and pushing it along at walking pace; the bike is
easy to control just by leaning it. Or just ride no hands.

You should read David Jones paper on the Unrideable Bicycle (_The
Stability of the Bicycle_, Physics Today 23, 34-36); you would find it
instructive. There's a PDF on the net somewhere but I've lost the link.

--
simon@jasmine.org.uk (Simon Brooke) http://www.jasmine.org.uk/~simon/

The Conservative Party is now dead. The corpse may still be
twitching, but resurrection is not an option - unless Satan
chucks them out of Hell as too objectionable even for him.

Mike Causer

On Sun, 12 Dec 2004 13:45:54 +0000, Simon Brooke wrote:

> You should read David Jones paper on the Unrideable Bicycle (_The
> Stability of the Bicycle_, Physics Today 23, 34-36); you would find it
> instructive. There's a PDF on the net somewhere but I've lost the link.

http://socrates.berkeley.edu/~fajan...JonesBikeBW.pdf

..... or so you posted this August.



Mike

Simon Brooke

in message
<pan.2004.12.12.14.25.59.898152@firstnamelastname.com.invalid>, Mike
Causer ('mikec@firstnamelastname.com.invalid') wrote:

> On Sun, 12 Dec 2004 13:45:54 +0000, Simon Brooke wrote:
>
>> You should read David Jones paper on the Unrideable Bicycle (_The
>> Stability of the Bicycle_, Physics Today 23, 34-36); you would find
>> it instructive. There's a PDF on the net somewhere but I've lost the
>> link.
>
>
http://socrates.berkeley.edu/~fajan...JonesBikeBW.pdf
>
> .... or so you posted this August.

Thanks, yes. I knew somebody would remember.

--
simon@jasmine.org.uk (Simon Brooke) http://www.jasmine.org.uk/~simon/

my other car is #<Subr-Car: #5d480>
;; This joke is not funny in emacs.

Mike Causer

On Sun, 12 Dec 2004 20:31:32 +0000, Simon Brooke wrote:

> Thanks, yes. I knew somebody would remember.

In truth, Google remembered for me ......


.... up till today I'd just used the report of Daedelus' findings in
D.G. Wilson's "Bicycling Science" 3rd Ed.



Mike

[Not Responding]

On Sun, 12 Dec 2004 20:31:32 +0000, Simon Brooke
<simon@jasmine.org.uk> wrote:

>in message
><pan.2004.12.12.14.25.59.898152@firstnamelastname.com.invalid>, Mike
>Causer ('mikec@firstnamelastname.com.invalid') wrote:
>
>> On Sun, 12 Dec 2004 13:45:54 +0000, Simon Brooke wrote:
>>
>>> You should read David Jones paper on the Unrideable Bicycle (_The
>>> Stability of the Bicycle_, Physics Today 23, 34-36); you would find
>>> it instructive. There's a PDF on the net somewhere but I've lost the
>>> link.
>>
>>
>http://socrates.berkeley.edu/~fajan...JonesBikeBW.pdf
>>
>> .... or so you posted this August.
>
>Thanks, yes. I knew somebody would remember.

Now that we've sorted whether you turn left or right to turn left, can
we move on to whether the wheel hangs or rests on the spokes please.

Only joking.

James Annan

Simon Brooke wrote:
> in message <321gopF3hf77mU1@individual.net>, James Annan
> ('still_the_same_me@hotmail.com') wrote:
>
>
>>Your logic is broken, I'll merely point out that the countersteering
>>is NOT "in effect a short turn in the other direction", it is in fact
>>a loss of balance in which the _bicycle_ (contact patch) moves to one
>>side while the _rider_ is left behind. If you did it for more than a
>>brief moment, you would fall off, not turn.
>
>
> I suggest you try riding a bicycle. You will find that if you lean the
> bicycle to one side, it will turn to that side, without any need for
> any other steering input. If you lean your body to one side, thus
> moving your centre of gravity, then the bike will naturally lean to the
> other side, and thus you can easily initiate a turn in either
> direction.


I agree that it is possible to tip the bicycle to one side while riding
along no-hands. I suggest you consider what happens when an
intantaneously balanced rider does this. Since there is no external
lateral force (I assume from your snipping of my question on this point
that you do not dispute it) then for the bicycle to move a little to the
left, the rider's CoG must move a rather smaller distance to the right.

So we have the bicycle marginally to the left of the rider, and turning
further to the left.

In the immortal words of David Vine,

"What happens next"?


> You should read David Jones paper on the Unrideable Bicycle (_The
> Stability of the Bicycle_, Physics Today 23, 34-36); you would find it
> instructive. There's a PDF on the net somewhere but I've lost the link.

You should try not to be so patronising from a position of ignorance.
You made an arse of yourself only a couple of weeks ago when trying to
pontificate about mathematical concepts that you did not understand. I
doubt anyone needs the lesson reinforced. I certainly don't.

I'll repeat the question from my previous email:

>> One can initiate a
>> turn by any means which moves the CoG away from vertically above the
>> track. Sudden body movements exploiting inertia do this easily - so
>> easily, in fact, that it's instinctive.
>
>
> Can you describe such a movement, with particular reference to the source of the external lateral force that is required to move the CoG to one side? You might like to think of it as a torque around the wheel contact patch since the motion can also be viewed as a rotation about that point. (This takes the contact point out of the picture entirely.)

Once you accept that (for a balanced rider, eg CoG vertically above tyre
contact patch and riding straight ahead) there are no external forces
that can move the combined CoG of bike and rider to one side, it is an
immediate corollary that the only way to turn to the right, is to make
the contact patch move to the left relative to the CoG. That is all that
"countersteering" means.

James
--
If I have seen further than others, it is
by treading on the toes of giants.
http://www.ne.jp/asahi/julesandjames/home/

Jon Senior

James Annan wrote:
> Once you accept that (for a balanced rider, eg CoG vertically above tyre
> contact patch and riding straight ahead) there are no external forces
> that can move the combined CoG of bike and rider to one side, it is an
> immediate corollary that the only way to turn to the right, is to make
> the contact patch move to the left relative to the CoG. That is all that
> "countersteering" means.

I'm sure that I will regret getting involved in this one but...

Can't the balanced rider just lean from the hips. I'm writing this while
leaning slightly to the right in my chair (In fact, I look a prat
because I'm concentrating on the screen while randomly leaning from side
to side). I see no reason why this cannot be done on a bike and it would
then move the CoG away from the contact patch.

Jon

David Martin

[Not Responding] wrote:

> Now that we've sorted whether you turn left or right to turn left, can
> we move on to whether the wheel hangs or rests on the spokes please.

Given the ominous creaks from Igor's back wheel, I think even the spokes
are arguing about that one.

Must threaten it with a spoke key..

...d

Simon Brooke

in message <323rgsF3i1binU1@individual.net>, James Annan
('still_the_same_me@hotmail.com') wrote:

> Simon Brooke wrote:
>> in message <321gopF3hf77mU1@individual.net>, James Annan
>> ('still_the_same_me@hotmail.com') wrote:
>>
>>>Your logic is broken, I'll merely point out that the countersteering
>>>is NOT "in effect a short turn in the other direction", it is in fact
>>>a loss of balance in which the _bicycle_ (contact patch) moves to one
>>>side while the _rider_ is left behind. If you did it for more than a
>>>brief moment, you would fall off, not turn.
>>
>> I suggest you try riding a bicycle. You will find that if you lean
>> the bicycle to one side, it will turn to that side, without any need
>> for any other steering input. If you lean your body to one side, thus
>> moving your centre of gravity, then the bike will naturally lean to
>> the other side, and thus you can easily initiate a turn in either
>> direction.
>
> I agree that it is possible to tip the bicycle to one side while
> riding along no-hands. I suggest you consider what happens when an
> intantaneously balanced rider does this. Since there is no external
> lateral force (I assume from your snipping of my question on this
> point that you do not dispute it) then for the bicycle to move a
> little to the left, the rider's CoG must move a rather smaller
> distance to the right.
>
> So we have the bicycle marginally to the left of the rider, and
> turning further to the left.
>
> In the immortal words of David Vine,
>
> "What happens next"?

You adjust your balance and carry on normally. As to how you do this,
see below.

>> You should read David Jones paper on the Unrideable Bicycle (_The
>> Stability of the Bicycle_, Physics Today 23, 34-36); you would find
>> it instructive. There's a PDF on the net somewhere but I've lost the
>> link.
>
> You should try not to be so patronising from a position of ignorance.

And he himself has said it, so it must be to his credit...

> I'll repeat the question from my previous email:
>
>>> One can initiate a
>>> turn by any means which moves the CoG away from vertically above the
>>> track. Sudden body movements exploiting inertia do this easily - so
>>> easily, in fact, that it's instinctive.
>>
>> Can you describe such a movement, with particular reference to the
>> source of the external lateral force that is required to move the CoG
>> to one side? You might like to think of it as a torque around the
>> wheel contact patch since the motion can also be viewed as a rotation
>> about that point. (This takes the contact point out of the picture
>> entirely.)

Certainly. The issue is entirely in the rapidity of acceleration and
deceleration of body movement, exploiting inertia. If it were not
possible to adjust balance in this way, riding a unicycle, for
instance, or walking on a tightrope, would be impossible. Yet they are
not. If it can be done on a tightrope, why is it impossible on a
bicycle?

--
simon@jasmine.org.uk (Simon Brooke) http://www.jasmine.org.uk/~simon/
Ye hypocrites! are these your pranks? To murder men and give God thanks?
Desist, for shame! Proceed no further: God won't accept your thanks for
murther
-- Roburt Burns, 'Thanksgiving For a National Victory'

Simon Brooke

in message <1102892592.11594.0@sabbath.news.uk.clara.net>, Jon Senior
<jon_AT_restlesslemon_DOT_co_DOT_uk> ('') wrote:

> James Annan wrote:
>> Once you accept that (for a balanced rider, eg CoG vertically above
>> tyre contact patch and riding straight ahead) there are no external
>> forces that can move the combined CoG of bike and rider to one side,
>> it is an immediate corollary that the only way to turn to the right,
>> is to make the contact patch move to the left relative to the CoG.
>> That is all that "countersteering" means.
>
> I'm sure that I will regret getting involved in this one but...
>
> Can't the balanced rider just lean from the hips. I'm writing this
> while leaning slightly to the right in my chair (In fact, I look a
> prat because I'm concentrating on the screen while randomly leaning
> from side to side). I see no reason why this cannot be done on a bike
> and it would then move the CoG away from the contact patch.

Err, no it wouldn't. James is right about that. Provided it is done
slowly and smoothly, as you lean left, the bike leans right, keeping
the CoG more or less in the same place WRT the track. Try it when
you're riding no hands some time: this is one method by which you can
initiate turns (and, to be honest, I don't know of any other when
riding no hands).

Imagine standing on a tightrope. If you move your upper body slowly to
the left, your hips must move right. You can do this just by standing
on a line on the floor. The reason is that your only contact with the
world is the line, and, as James rightly points out, you have no
purchase or leverage to rotate your mass around that line.

The line or tightrope has some of the physics of a bike. On a bike, the
line is the track. However, on a bike, unlike a tightrope, the line can
be moved WRT the mass, by steering.

However, while we're on this subject, a suggestion for James. Stand on a
line on the floor, or the edge of a plank, or some similar object, one
foot in front of the other. Stand as still as you can. After a time you
will inevitably begin to fall to one side or the other. What
instinctive body movements do you make to correct your balance?

I think you will find that you make jerky movements of your shoulders
and arms. I think you will find that, some of the time at least, the
inertia from these jerky movements is sufficient to correct your
balance. If so, you must concede that this instinctive exploitation of
inertia gives you sufficient torque around the line to actually move
your centre of gravity. And if it works standing on a line, why can it
not work on a bicycle?

--
simon@jasmine.org.uk (Simon Brooke) http://www.jasmine.org.uk/~simon/

[ This mind intentionally left blank ]

Simon Brooke

in message <esdpr019cpumjopealkqatm6tss2h2bfc8@4ax.com>, [Not
Responding] ('not_responding@dev.null.invalid') wrote:

> Now that we've sorted whether you turn left or right to turn left, can
> we move on to whether the wheel hangs or rests on the spokes please.

I'm not going to hang around for that. I couldn't stand it...

--
simon@jasmine.org.uk (Simon Brooke) http://www.jasmine.org.uk/~simon/
Das Internet is nicht fuer gefingerclicken und giffengrabben... Ist
nicht fuer gewerken bei das dumpkopfen. Das mausklicken sichtseeren
keepen das bandwit-spewin hans in das pockets muss; relaxen und
watchen das cursorblinken. -- quoted from the jargon file

James Annan

Simon Brooke wrote:


> The line or tightrope has some of the physics of a bike. On a bike, the
> line is the track. However, on a bike, unlike a tightrope, the line can
> be moved WRT the mass, by steering.

That's bass-ackwards, of course. The tightrope can (and does) move
sideways under the performer. Look at those two brackets, and imagine
them to be a view of the performer from the rear. The left bracket has
the feet to the right of the CoG, and vice-versa. The bicycle contact
patch can only move sideways if the bicycle is steered to the side.

> I think you will find that you make jerky movements of your shoulders
> and arms. I think you will find that, some of the time at least, the
> inertia from these jerky movements is sufficient to correct your
> balance. If so, you must concede that this instinctive exploitation of
> inertia gives you sufficient torque around the line to actually move
> your centre of gravity. And if it works standing on a line, why can it
> not work on a bicycle?

Well, standing on a single foot is not much problem for someone with
decent balance - it provides a platform several inches across and
twisting one's ankle can shift the effective pressure point from one
side to the other, giving a fair bit of wobble room before one risks
overbalancing. As the support gets narrower, it gets much harder, until
one (well, me at least) can only resort to increasingly desperate and
wild waving around of the arms. This can generate small temporary
torques, but has little to do with normal bike riding (even hands off)
and only prolongs the inevitable for a few seconds.

If you think you can control your balance a bicycle by this method, then
you should also be able to ride one in which the fork is locked straight
ahead. A few circus performers might be able to manage it, but 99.9% of
riders certainly cannot, and it has nothing to do with normal riding.

James
--
If I have seen further than others, it is
by treading on the toes of giants.
http://www.ne.jp/asahi/julesandjames/home/

James Annan

Simon Brooke wrote:


>>So we have the bicycle marginally to the left of the rider, and
>>turning further to the left.
>>
>>In the immortal words of David Vine,
>>
>>"What happens next"?
>
>
> You adjust your balance and carry on normally. As to how you do this,
> see below.
>

> Certainly. The issue is entirely in the rapidity of acceleration and
> deceleration of body movement, exploiting inertia. If it were not
> possible to adjust balance in this way, riding a unicycle, for
> instance, or walking on a tightrope, would be impossible. Yet they are
> not. If it can be done on a tightrope, why is it impossible on a
> bicycle?
>

As I've already mentioned, the tightrope moves laterally under the
performer. This is also a trick that takes quite some skill (I doubt
many would go to the circus just to see a normal cyclist riding along).
A unicycle is also moved under the rider, in the fore-aft plane as well
as from side to side. The relevance of that to your point is not clear,
but then again, your point is not clear in itself.

Now, back to the cyclist. Assume this time he is not a circus performer.
How does he apply sufficient torque to himself to move himself bodily
from one side to the other of the contact patch. If you believe he can
do this, do you also believe he can ride a bicycle with the forks locked
straight ahead? If not, why not? Surely the same "adjust your balance
annd carry on normally" trick should work there too, shouldn't it?

James
--
If I have seen further than others, it is
by treading on the toes of giants.
http://www.ne.jp/asahi/julesandjames/home/

Simon Brooke

in message <325b97F3gr7ciU1@individual.net>, James Annan
('still_the_same_me@hotmail.com') wrote:

> until one (well, me at least) can only resort to increasingly
> desperate and wild waving around of the arms. This can generate small
> temporary torques,

Thank you, that is what I said.

> but has little to do with normal bike riding (even
> hands off)

Evidence, please? I believe it has everything to do with normal bike
riding. You are, of course, correct that balancing on a _moving_ bike
is substantially easier than balancing on the edge of a plank, but that
is because very small control inputs ('small temporary torques', in
your own words) are sufficient, in conjunction with the sensitive
lean-steering of a conventional bicycle, to keep the show on the road.

--
simon@jasmine.org.uk (Simon Brooke) http://www.jasmine.org.uk/~simon/

Age equals angst multiplied by the speed of fright squared.
;; the Worlock