balance

Quoted message said:

[email hidden] wrote:

[snip]

Quoted message said:

Quoted message said:

Fantastic riders can balance sitting down, no hands, on two motionless
wheels.

With the steering all the way to the side I presume. This is a trick I
use to wow the kids down at the LBS so I can get free access to their
truing stand!

[snip]

Dear Joseph,

No, the really good ones don't even need to [censored] the damned wheel,
curse them!

http://groups.google.com/group/rec.bicycles.misc/msg/5af49354d35d38aa

Cheers,

Carl Fogel

Paul Hobson said:

Paul Hobson said:

Dan said:

david wrote:
> Can somebody please explain why a moving bicycle is easier to balance
> than a stationary one.

Actually, it is impossible to balance a stationary bicycle.

Oops. I guess this guy didn't get the memo. While he does bounce a
lot of the time, there are instances where he is truly stationary.

<http://video.google.com/videoplay?docid=-8727079186070973755&q=bike+trials>

<http://video.google.com/videoplay?docid=-8551222727971975773&q=bike+trials>

maybe that one's better? (skip ahead to 2 min into the video)

Yeah, I've seen such things. My point is that it cannot be done without
motion of some sort. The rider has to hop or roll. You can pause
momentarily but the bike is actually slowly starting to tip, the initial
lateral motion is just very slow. In a classic track stand the rider
pedals back and forth with the front wheel turned. On a freewheel bike
you need a slight incline so you can roll backward and pedal forward. A
stationary bike is unstable and will not stand up, simply take yours out
to the street and see how long you can get it to stand stationary
without a rider on board.

A pencil standing on its point can seem to stand for a moment but it is
unstable and never motionless. With a little statics and a Free Body
Diagram (FBD) the pencil seems at first look to be in static equilibrium:

/-----\
1 1
1 1
------- Y
-------
1 1 1
1 1 1
1 1 1---- X
1 1
1 1
1 W 1
1 1
1 1
1 1
1 1
1/\/\/1
\ /
\ /
\ /
V

In the idealized FBD, there are only two forces acting on the pencil, a
vertical downward force at the center of mass "W" and a vertical upward
reaction force "R" at the contact point. Sum of the forces X = zero so
no acceleration X. Sum of the forces Y = -W + R = 0 so no acceleration
Y. Sum of the moments about the tip = W(0) = 0 so no rotational
acceleration. The pencil seems to be stable and not move but we know
that isn't the case. It is in "Unstable Equilibrium."

In actual fact, the moment equation is wrong because the center of mass
cannot be precisely aligned over the contact point so the equation is
something like W(0.00000000001) which is not equal to zero. Also, there
are small lateral forces due to air motion, moving masses in the area,
ground vibration, even sound waves which make the moment equation look like:
W(not zero) + F(h) = (not zero)
Also, it is impossible to start with the pencil at zero rotational
velocity, zero is simply not a practical possibility for alignment or
for rotational velocity. The result is that unless the pencil has a
large enough flat tip to counteract the secondary influences, it tips
over. A bike with round tires is the same.

The exception would be if you put a very wide tire with a flat tread on
the bike, like a wide slick, or put down the kickstand.

See:
http://www.diracdelta.co.uk/science/source/e/q/equilibrium/source.html
http://selland.boisestate.edu/jbrennan/physics/notes/Force/statics.htm

Quoted message said:

Quoted message said:

[email hidden] wrote:

[snip]

Quoted message said:

Quoted message said:

Fantastic riders can balance sitting down, no hands, on two motionless
wheels.

With the steering all the way to the side I presume. This is a trick I
use to wow the kids down at the LBS so I can get free access to their
truing stand!

[snip]

Dear Joseph,

No, the really good ones don't even need to [censored] the damned wheel,
curse them!

http://groups.google.com/group/rec.bicycles.misc/msg/5af49354d35d38aa

Cheers,

Carl Fogel

I suppose using indexed steering is cheating. No chance for me straight
ahead, the bars always flop to the side.

Joseph

Absent Husband said:

david said:

Can somebody please explain why a moving bicycle is easier to balance
than a stationary one.

Maybe you can work this out for yourself!!

Think about - what is the difference between a moving bike and a
stationary one (ie. what two big round things are doing something
different in each case??). That might start you on the right track,
yes?? 😉

If you're going to make snide remarks, it's better to be right. There has
been considerable discussion about the gyroscopic effect of the wheels,
but the bottom line is that that is not what allows you to balance on a
bike. People have designed bikes with counter-rotating wheels to cancel
the gyroscopic effect, and the bike is still ridable. You can also
balance quite well while barely moving, in which case there is essentially
no gyroscopic effect. Lots of us can balance on a bike while it is not
moving forward at all (called a track stand). Actually, that practice
shows what we really do, in that you can't do a track stand without the
front wheel being turned at a significant angle. Then, pushing forward on
the pedals tilts the bike to one side, pushing back (on a fixed gear)
tilts it to the other. You do the same thing while riding by turning the
wheel slightly and/or leaning -- you don't even notice it, usually.

--

David L. Johnson

And though I have the gift of prophecy, and understand all mysteries,
and all knowledge; and though I have all faith, so that I could remove
mountains, and have not charity, I am nothing. [1 Corinth. 13:2]

ddog said:

david said:

Quoted message said:

Can somebody please explain why a moving bicycle is easier to balance
than a stationary one.

Momentum is an additional force to keep you balanced.

No. Momentum is not a force.

Quoted message said:

Only good reason for compact cranks
other than phsical size constraints, but larger cranks are better
leverage and leg muscle extentions most of the time spinning.

At the end of this odd bit of doggerel was this sentence. What do compact
cranks have to do with balance? "Compact" cranks refer to those with
smaller chainrings, not shorter arms.

--

David L. Johnson

And though I have the gift of prophecy, and understand all mysteries,
and all knowledge; and though I have all faith, so that I could remove
mountains, and have not charity, I am nothing. [1 Corinth. 13:2]

Ben C said:

I will attempt to explain.

Momentum is the product of force and velocity.

Try again. Momentum is the product of mass and velocity.

Quoted message said:

Impulse is the product (integral strictly) of force and time. If you
give something a knock with a hammer,

Your example is closer than your description, which is not correct, and
calling it an integral doesn't help.

or with a puff of wind, you apply

Quoted message said:

a bit of force for a bit of time, which adds up to an "impulse".

Newton's second law of physics tells us that a given impulse will
produce a given change of momentum.

No, again. Newton's second law says that the net force on a body is
equal to the mass times the accleration.

Quoted message said:

right (going round a left-hand curve always throws you to the right--
centrifugal force),

A more expected error. There is no centrifugal force. The force is from
the acceleration of the cyclist making the turn. What you feel
"pushing" you the other way is actually your momentum, which is
following Newton's first law, tending to stay in motion in the same
direction.

Quoted message said:

bike can be controlled. I believe this is the basic mechanism, but keep
an eye on this thread because I could be wrong.

--

David L. Johnson

And though I have the gift of prophecy, and understand all mysteries,
and all knowledge; and though I have all faith, so that I could remove
mountains, and have not charity, I am nothing. [1 Corinth. 13:2]

Dan said:

Paul Hobson said:

Paul Hobson said:

Dan wrote:
> david wrote:
>> Can somebody please explain why a moving bicycle is easier to balance
>> than a stationary one.
>
> Actually, it is impossible to balance a stationary bicycle.

Oops. I guess this guy didn't get the memo. While he does bounce a
lot of the time, there are instances where he is truly stationary.

<http://video.google.com/videoplay?docid=-8727079186070973755&q=bike+trials>

<http://video.google.com/videoplay?docid=-8551222727971975773&q=bike+trials>

maybe that one's better? (skip ahead to 2 min into the video)

Yeah, I've seen such things. My point is that it cannot be done without
motion of some sort. The rider has to hop or roll. You can pause
momentarily but the bike is actually slowly starting to tip, the initial
lateral motion is just very slow. In a classic track stand the rider
pedals back and forth with the front wheel turned. On a freewheel bike
you need a slight incline so you can roll backward and pedal forward. A
stationary bike is unstable and will not stand up, simply take yours out
to the street and see how long you can get it to stand stationary
without a rider on board.

But there is a rider on board.

Greg

--
"All my time I spent in heaven
Revelries of dance and wine
Waking to the sound of laughter
Up I'd rise and kiss the sky" - The Mekons

David L. Johnson said:

Ben C said:

I will attempt to explain.

Momentum is the product of force and velocity.

Try again. Momentum is the product of mass and velocity.

Sorry! Yes of course it is.

Quoted message said:

Quoted message said:

Impulse is the product (integral strictly) of force and time. If you
give something a knock with a hammer,

Your example is closer than your description, which is not correct, and
calling it an integral doesn't help.

So what is an impulse then?

Quoted message said:

or with a puff of wind, you apply

Quoted message said:

a bit of force for a bit of time, which adds up to an "impulse".

Newton's second law of physics tells us that a given impulse will
produce a given change of momentum.

No, again. Newton's second law says that the net force on a body is
equal to the mass times the accleration.

F = ma.

Integrate both sides against time, you get Impulse = Change of momentum.

I consider the physics to be the same, and therefore Impulse = Change of
momentum to be a statement of the second Law.

Quoted message said:

Quoted message said:

right (going round a left-hand curve always throws you to the right--
centrifugal force),

A more expected error. There is no centrifugal force.

This is a matter of interpretation. I'm happy with the idea of
centrifugal force so long as there is no misunderstanding.

Quoted message said:

The force is from the acceleration of the cyclist making the turn.
What you feel "pushing" you the other way is actually your momentum

Your momentum doesn't "push" you. Forces push.

Quoted message said:

, which is following Newton's first law, tending to stay in motion in
the same direction.

Yes indeed.

david who? said:

Can somebody please explain why a moving bicycle is easier to
balance than a stationary one.

Is this a troll or what! How about trying this with an in-line skate
or ice skate. I'm sure you can glide on one skate effortlessly until
you come to a stop. As speed approaches zero balancing becomes much
more difficult. You may discover what keeps a single track vehicle
upright if you give this some thought.

Jobst Brandt

In article <[email hidden]>,

David L. Johnson said:

ddog said:

david said:

> Can somebody please explain why a moving bicycle is easier to
> balance than a stationary one.

Momentum is an additional force to keep you balanced.

No. Momentum is not a force.

Quoted message said:

Only good reason for compact cranks other than phsical size
constraints, but larger cranks are better leverage and leg muscle
extentions most of the time spinning.

At the end of this odd bit of doggerel was this sentence. What do
compact cranks have to do with balance? "Compact" cranks refer to
those with smaller chainrings, not shorter arms.

Wouldn't that be ddoggerel?

Quoted message said:

david said:

Can somebody please explain why a moving bicycle is easier to balance
than a stationary one.

Wilfred said:

Take off the front wheel and hold the wheel by the axle. Then start it
spinning. Now try to turn the axle sideways 90 degrees , as it would do
when falling over when fixed to the bike.
See how hard it is.
Also when riding you have the opportunity to keep shifting the point of
contact on the road to keep it under the center of gravity. ie, you can
weave around slightly, or a lot.

I didn't reply to the OP because I cannot succinctly explain it myself
and I don't believe all is even known.

Regarding "gyroscopic effect", the paper "building an Unrideable
Bicycle" covered that in an elegant experiment some 45 years ago.
Mounting a second front wheel next to the original just off the ground,
driven to spin in reverse, has no effect on handling whatsoever.

Your last paragraph is much better but the details of that are not trivial.

--
Andrew Muzi
www.yellowjersey.org
Open every day since 1 April, 1971

In article
<[email hidden]>,

Ben C said:

ddog said:

david said:

> Can somebody please explain why a moving bicycle is easier to balance
> than a stationary one.

Momentum is an additional force to keep you balanced.

Momentum isn't a force.

I will attempt to explain.

Momentum is the product of force and velocity.

Wrong. Remainder of the message has been excised for safety.

--
Michael Press

G.T. said:

Dan said:

Paul Hobson said:

Paul Hobson wrote:
> Dan wrote:
>> david wrote:
>>> Can somebody please explain why a moving bicycle is easier to balance
>>> than a stationary one.
>>
>> Actually, it is impossible to balance a stationary bicycle.
>
> Oops. I guess this guy didn't get the memo. While he does bounce a
> lot of the time, there are instances where he is truly stationary.
>
> <http://video.google.com/videoplay?docid=-8727079186070973755&q=bike+trials>
>

<http://video.google.com/videoplay?docid=-8551222727971975773&q=bike+trials>

maybe that one's better? (skip ahead to 2 min into the video)

Yeah, I've seen such things. My point is that it cannot be done
without motion of some sort. The rider has to hop or roll. You can
pause momentarily but the bike is actually slowly starting to tip, the
initial lateral motion is just very slow. In a classic track stand the
rider pedals back and forth with the front wheel turned. On a
freewheel bike you need a slight incline so you can roll backward and
pedal forward. A stationary bike is unstable and will not stand up,
simply take yours out to the street and see how long you can get it to
stand stationary without a rider on board.

But there is a rider on board.

Greg

True and the rider is moving. The difference is the difference between
dynamic equilibrium and static equilibrium. In static equilibrium
nothing is moving. As far as the stability of a stationary bike goes,
there is no significant difference between the stability of a riderless
bike and one with a statue sitting on it. David said "truly stationary"
and I suppose we need to figure out what it means. To me it means
nothing is moving. To you it may mean the wheels are not rotating. Whatever.

Michael Press said:

In article
<[email hidden]>,

Ben C said:

ddog said:

david wrote:
> > Can somebody please explain why a moving bicycle is easier to balance
> > than a stationary one.

Momentum is an additional force to keep you balanced.

Momentum isn't a force.

I will attempt to explain.

Momentum is the product of force and velocity.

Wrong.

I know, slip of the tongue etc. I meant to say "mass and velocity".

Quoted message said:

Remainder of the message has been excised for safety.

You are wise to take such precautions, but I think the remainder was
mostly all right.

Quoted message said:

Is this a troll or what!

That was my first impression. According to google
http://tinyurl.com/ys5hm7
he has 8 posts over the past year and a half using several names.
Netscan has similar:
http://tinyurl.com/2bokmy
The other posts look benign enough. Could simply be someone who is
unfamiliar with RBT and asking a valid question.

Carl Fogel said:

Really good riders can balance on two motionless wheels--they shift
their weight so delicately that they never go out of balance enough to
need to move the contact patch.

Quoted message said:

Fantastic riders can balance sitting down, no hands, on two motionless
wheels.

Quoted message said:

Really annoying acrobats can balance standing on the seat, or doing a
single-arm handstand on the seat.

That reminds me of a great moment when I visited the Cinelli plant
years ago to get some parts for my Cinelli bicycle and say hello. I
had met the Cinellis on my first tour of the alps in 1959 and kept in
touch over the years I lived in Europe and made a point of visiting
their place at 45 Egidio Folli, Lambrate Milano.

I ride a large frame but that didn't deter Cino, a great racer in this
time with Tullio Campagnolo, was a short man in slacks and white shirt
with fine street shoes. Shoving off from the stairs in front of his
office, he rode my bicycle using the pedals in the horizontal
position, sat down, stopped the bicycle and crossed his arms over his
chest and held that pose, motionless for a good 15 seconds, just to
show me that an old guy can still ride bike.

In retirement he lived to 100 years in his home town of Chiancano
south of Florence. He was one of my great heroes who when asked, said
the greatest road in the Alps is the Stelvio bar none, although he
thought I might not like it because it was unpaved on the west
(Italian) slope, in contrast to the Tirolean side that was elegantly
paved with stone and concrete revetments for the 48 hairpin turns to
Trafoi.

I vote with Cino. It IS the greatest road!

http://www.paloaltobicycles.com/alps_photos/i12.html

Press NEXT to see its beauty.

Jobst Brandt

"Ben C" wrote: (clip) Momentum is the product of force and velocity (clip)
^^^^^^^^^^^^^^^^^
It's not really relevant here, but force x velocity = power.

Answering the OP's original question: A moving bicycle is easier to balance
because steering corrections move the wheels under the rider.

Tim McNamara said:

Quoted message said:

Quoted message said:

Can somebody please explain why a moving bicycle is easier to
balance than a stationary one.

Quoted message said:

Quoted message said:

Actually, it is impossible to balance a stationary bicycle.

Quoted message said:

It's not impossible. It's possible to balance a motionless bicycle
for a few seconds. People think of track standing as "stationary"
but of course it is not.

That depends on who is doing it. The definition of motionless in this
case meaning wheel rotation.

By the way, those who haven't seen Joe E Brown, 'The Six Day Racer'
should make an effort to see this old classic. It is full of stunt
riding in Brown's inimitable wacky style with real indoor racing.

Jobst Brandt

I can assure you that a troll was not intended!
I would just like a clear scientific answer.

Quoted message said:

david who? said:

Can somebody please explain why a moving bicycle is easier to
balance than a stationary one.

Is this a troll or what! How about trying this with an in-line skate
or ice skate. I'm sure you can glide on one skate effortlessly until
you come to a stop. As speed approaches zero balancing becomes much
more difficult. You may discover what keeps a single track vehicle
upright if you give this some thought.

Jobst Brandt

A Muzi said:

Quoted message said:

david said:

Can somebody please explain why a moving bicycle is easier to balance
than a stationary one.

Dan said:

Actually, it is impossible to balance a stationary bicycle.

Tell that to the messengers poised at the stoplight. I can see them now
out my window.

Simply by rotating the handlebars one way or the other you can move the
bike from side to side even though the wheels aren't moving forward,
obviously it's because of the rake and trail of the steering mechanism.
Let's see someone try to trackstand on a bike built with no rake or
trail. Carl?

Friday