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Old 05-01-08, 09:26 AM   #1
JeanCoutu
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What would a weightless bike feel like?

Idly thinking about this today. I figure it would be incredibly twitchy, probably nearly impossible to ride without hands on any surface that isn't pool table smooth. Not comfortable to ride long distances.
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Old 05-01-08, 09:38 AM   #2
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marshmallow?
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Old 05-01-08, 11:00 AM   #3
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Like walking
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Old 05-01-08, 11:20 AM   #4
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Would be a lot faster then walking for sure
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Old 05-01-08, 12:38 PM   #5
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You wouldn't be able to keep your balance because the wheels have no mass.

Otherwise, it would be like riding a beam of light very slowly.
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Old 05-01-08, 01:02 PM   #6
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thread hijack;

HOV, your sig line sounds like a bobby knight quote.

wasn't he the one who also said, "if **** is inevitable, you may as well enjoy it."
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Old 05-01-08, 01:40 PM   #7
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You wouldn't be able to keep your balance because the wheels have no mass.

Otherwise, it would be like riding a beam of light very slowly.
The OP said weightless, not massless. The wheels will still have mass, therefore still have rotational inertia.
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Old 05-01-08, 01:58 PM   #8
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Light?
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Old 05-01-08, 03:25 PM   #9
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I don't think it would be any big problem. At least I haven't heard anyone riding lighter bikes complaining because they were too light. Maybe some of those carbon fiber manufacturers have to slip a few lead slugs in some of their bikes to keep them controllable, but I sort of doubt it.
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Old 05-01-08, 03:33 PM   #10
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you'd basically just feel your own body weight being moved around.
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Old 05-01-08, 04:34 PM   #11
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The OP said weightless, not massless. The wheels will still have mass, therefore still have rotational inertia.
But the mass and the rotational inertia of the wheels have little to do with balancing, steering, and riding a bicycle.

http://www.dclxvi.org/chunk/tech/trail/
Many people assume that the gyroscopic action of the front wheel is solely responsible for keeping a bicycle upright. In fact, its effect is minor. Gyroscopic stability is what keeps a rolling hoop from falling. One can demonstrate the gyroscopic forces on a bicycle wheel by holding a detached, still wheel by the ends of its axle. Tilt the axle up and down, without letting it twist left or right. In other words, put one hand higher than the other without letting either hand move forwards or back. Then spin the wheel forward, and tilt it again. When the axle is tilted so that the left side is down, it will twist left, and when it is tilted with the right side down, it will twist right. This is exactly how we want the wheel to move when we ride a bike, and is similar to the effects of trail.

So why do we say that this doesn't really affect bicycle handling? David Jones explored this when he tried to make an unridable bicycle. His first attempt, the URB Mark 1, negated the gyroscopic action of the front wheel by mounting another wheel on the same axle and spinning it in the opposite direction. He says that it felt strange, but was easily ridable. However, when set in motion without a rider, it collapsed much quicker than normal, and he found it difficult (although not impossible) to ride with his hands off of the handlebars.
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Old 05-01-08, 04:54 PM   #12
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But the mass and the rotational inertia of the wheels have little to do with balancing, steering, and riding a bicycle.

http://www.dclxvi.org/chunk/tech/trail/
Many people assume that the gyroscopic action of the front wheel is solely responsible for keeping a bicycle upright. In fact, its effect is minor. Gyroscopic stability is what keeps a rolling hoop from falling. One can demonstrate the gyroscopic forces on a bicycle wheel by holding a detached, still wheel by the ends of its axle. Tilt the axle up and down, without letting it twist left or right. In other words, put one hand higher than the other without letting either hand move forwards or back. Then spin the wheel forward, and tilt it again. When the axle is tilted so that the left side is down, it will twist left, and when it is tilted with the right side down, it will twist right. This is exactly how we want the wheel to move when we ride a bike, and is similar to the effects of trail.

So why do we say that this doesn't really affect bicycle handling? David Jones explored this when he tried to make an unridable bicycle. His first attempt, the URB Mark 1, negated the gyroscopic action of the front wheel by mounting another wheel on the same axle and spinning it in the opposite direction. He says that it felt strange, but was easily ridable. However, when set in motion without a rider, it collapsed much quicker than normal, and he found it difficult (although not impossible) to ride with his hands off of the handlebars.
According to that quote, gyroscopic force does have an effect.

I haven't ridden such a bike, but I can't stand stationary on mine without falling over (track stands don't count). I'm guessing that, when I'm moving, the spinning wheels help me stay upright.
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Old 05-01-08, 04:57 PM   #13
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How would a weightless bike feel? Get on a bike, ride off the top of a cliff, and find out. Probably won't have the time to share your findings with the world though...
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Old 05-01-08, 06:03 PM   #14
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Idly thinking about this today. I figure it would be incredibly twitchy, probably nearly impossible to ride without hands on any surface that isn't pool table smooth. Not comfortable to ride long distances.
more impressive would be a frictionless rider and bike, like that ship at the restaurant at the end of the universe in the HGttG series.
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Old 05-01-08, 07:46 PM   #15
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Originally Posted by BarracksSi View Post
According to that quote, gyroscopic force does have an effect.

I haven't ridden such a bike, but I can't stand stationary on mine without falling over (track stands don't count). I'm guessing that, when I'm moving, the spinning wheels help me stay upright.
Well, I didn't say "no effect".

Many people assume that the gyroscopic action of the front wheel is solely responsible for keeping a bicycle upright. In fact, its effect is minor.

Try reading the rest of the item I linked.

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Old 05-01-08, 08:21 PM   #16
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"I haven't ridden such a bike, but I can't stand stationary on mine without falling over (track stands don't count). I'm guessing that, when I'm moving, the spinning wheels help me stay upright."

Actually, it's the fact that you can steer in such a way as to easily correct your balance. People have built ski-type thingies that work by the same principle and they work just fine even though nothing is rotating.
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Old 05-01-08, 08:52 PM   #17
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Actually, it's the fact that you can steer in such a way as to easily correct your balance. People have built ski-type thingies that work by the same principle and they work just fine even though nothing is rotating.
I can stand all day on skis.

Buuuut -- you're right about being able to steer the bike back under the rider for balance. It wasn't until after I posted that I realized that 3-mph creeping on the bike doesn't generate much gyroscopic force at all, yet I can keep from falling down anyway.
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Old 05-02-08, 06:10 AM   #18
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The OP said weightless, not massless. The wheels will still have mass, therefore still have rotational inertia.
Weight = (mass) * (acceleration due to gravity). If mass = zero, then weight = zero.

If something has a mass of 1 kg, then its weight on the surface of the Earth is 9.8 Newtons. A common misnomer is that "pounds" or "kilograms" measure weight - they don't. They are a measure of mass, and only become weight when placed under the influence of gravity. At that point, the measurement of lb. or kg. isn't valid any more. Our trade/business conventions are wrong in terms of physics.

But yes, I did assume that the gyroscopic effect kept the bike stable. Having read that snippet, I suppose it's a combination of velocity and gyroscopic effec that keep the bike stable. I would assume that the gyroscopic effect would cancel out a lot of the human twitches and balance adjustments, making the ride as smooth and stable as we know bicycles to be. Without that, it would be twitchy and strange.
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Old 05-02-08, 06:13 AM   #19
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thread hijack;

HOV, your sig line sounds like a bobby knight quote.

wasn't he the one who also said, "if **** is inevitable, you may as well enjoy it."
Hmmm, dunno Mr, Knight. it's a quote from the heavy metal band "Rorschach Test". What you quoted there reminds me of the Tool song "Prison Sex", in which it is stated:

"I have found some kind of temporary sanity in this... s**t, blood and c** on my hands", which I suppose would be along the lines of enjoying it as Bobby Knight recommended.

Pearls of wisdom, man.
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Old 05-02-08, 06:33 AM   #20
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Weight = (mass) * (acceleration due to gravity). If mass = zero, then weight = zero.

If something has a mass of 1 kg, then its weight on the surface of the Earth is 9.8 Newtons. A common misnomer is that "pounds" or "kilograms" measure weight - they don't. They are a measure of mass, and only become weight when placed under the influence of gravity. At that point, the measurement of lb. or kg. isn't valid any more. Our trade/business conventions are wrong in terms of physics.

But yes, I did assume that the gyroscopic effect kept the bike stable. Having read that snippet, I suppose it's a combination of velocity and gyroscopic effec that keep the bike stable. I would assume that the gyroscopic effect would cancel out a lot of the human twitches and balance adjustments, making the ride as smooth and stable as we know bicycles to be. Without that, it would be twitchy and strange.

Well the OP didn't specifiy by what means the bike was weightless. Was it because it had no mass or because there was no presence of gravity?
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Old 05-02-08, 07:24 AM   #21
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I assume his thought experiment didn't include pedaling around in theoretical vacuum, so it must mean massless.

Even if the bike were to be far away from a large body, there would still be some small force of gravity between the wheels and the rider's body itself, hence weight. So to make the question valid, the wheels must be massless.
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Old 05-02-08, 09:22 AM   #22
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Weight = (mass) * (acceleration due to gravity). If mass = zero, then weight = zero.

If something has a mass of 1 kg, then its weight on the surface of the Earth is 9.8 Newtons. A common misnomer is that "pounds" or "kilograms" measure weight - they don't. They are a measure of mass, and only become weight when placed under the influence of gravity. At that point, the measurement of lb. or kg. isn't valid any more. Our trade/business conventions are wrong in terms of physics.
That's not correct. Kilograms are indeed a measure of mass, but pounds are a measure of weight or force.

F = ma

Force is the product of mass and acceleration. Weight is the product of mass and gravitational acceleration.

A mass of 1 kilogram weighs about 9.8 newtons on Earth. It also weighs about 2.2 pounds.
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Old 05-02-08, 10:31 AM   #23
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That's not correct. Kilograms are indeed a measure of mass, but pounds are a measure of weight or force.

F = ma

Force is the product of mass and acceleration. Weight is the product of mass and gravitational acceleration.

A mass of 1 kilogram weighs about 9.8 newtons on Earth. It also weighs about 2.2 pounds.
Indeed, as I said earlier, and as you re-stated, Weight = (Mass) * (Acceleration due to gravity). Nothing to argue there.

But by your own statement, you're wrong. Just look at the units for a Newton:

1. Force (in newtons) = Mass (in kg) * Acceleration (in meters per seconds squared)
2. N = (kg - m)/(sec^2)

Nowhere in the measure of units of a "pound" is there mentioned any component of acceleration. So a pound is only a measure of mass, and newtons =! pounds.

Kg is a measure of mass in the metric system, and lbs are a measure of mass in the standard system. It's only in commerce that the measures of mass are used interchangibly with "weight".

NIST Handbook 130 states this very clearly: V. "Mass" and "Weight." [NOTE 1, See page 6]
The mass of an object is a measure of the object’s inertial property, or the amount of matter it contains. The weight of an object is a measure of the force exerted on the object by gravity, or the force needed to support it. The pull of gravity on the earth gives an object a downward acceleration of about 9.8 m/s2. In trade and commerce and everyday use, the term "weight" is often used as a synonym for "mass." The "net mass" or "net weight" declared on a label indicates that the package contains a specific amount of commodity exclusive of wrapping materials. The use of the term "mass" is predominant throughout the world, and is becoming increasingly common in the United States. (Added 1993)
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Old 05-02-08, 10:38 AM   #24
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That's not correct. Kilograms are indeed a measure of mass, but pounds are a measure of weight or force.

F = ma

Force is the product of mass and acceleration. Weight is the product of mass and gravitational acceleration.

A mass of 1 kilogram weighs about 9.8 newtons on Earth. It also weighs about 2.2 pounds.
Here's the wiki link to the definition of a pound, in case you're not tracking that.

Weights and Measures Act 1963 (UK).

...the kilogram shall be the unit of measurement of mass by reference to which any measurement involving a measurement of length or mass shall be made in the United Kingdom; and... (b) the pound shall be 0453 592 37 kilogram exactly.


http://en.wikipedia.org/wiki/Pound_%28mass%29
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Old 05-02-08, 10:39 AM   #25
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I think the fact that you as a rider have mass and therefore inertia would compensate for the lack of rotational weight in the wheels. The bike would still be structurally holding you up so it might be a bit unwieldy when not riding (you would need to carry it as opposed rolling it with one hand) but when riding I think it would just be the same as if you had lost 15-20 pounds. You might get some extra vibration descending since there would be no mass in the frame to stabalize vibrations.
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