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  1. #176
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    Great stuff. Thanks for that bit of history.
    Casey Greene - Cartographer - Adventure Cycling Association
    http://greenecasey.blogspot.com

  2. #177
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    Quote Originally Posted by smilinsteve View Post
    Graham,
    I'm starting to see some of what I had missed earlier. I think the term "torque reaction" was throwing me off, but if a force acts away from the center of gravity, it creates a moment.
    Hi Steve, I like the drawing, it will definitely help to clarify the nature of the problem. I would have gone onto your technique of taking the sum of the moments acting on the CoG but thought is important to define the nature of torque reactions first. An alternate way of analysing the problem is by working out the sum of the vertical vector components and the horizontal vector components.

    The force that acts on the bike below the center of gravity does indeed create a moment but only when drive forces try to accelerate the CoG. These are what I call inertia forces/reaction forces but I believe that they are more commonly called weight transfer or load transfer forces.
    Weight transfer - Wikipedia, the free encyclopedia

    Weight transfer forces are similar but distinct from torque reaction forces in that they are only present in cases of acceleration or deceleration. Therefore, they do not apply to a Segway when it is climbing at a constant velocity. Torque reaction however, occurs whenever torque is present. For instance if you clamped the rear wheel of an electric bicycle to the floor and then started the motor in a low gear the front wheel would lift into the air even if the bicycle does not move forwards.



    Quote Originally Posted by smilinsteve View Post
    In my drawing, the front wheel is just starting to lift, so it has a normal force of zero. The rear tire contact patch is the fulcrum around which the COG is rotating.
    B is the vertical distance from the COg to the fulcrum and A is the horizontal distance to the fulcrum.
    F is the forward driving force from the tire/ground force, which we can say is acting at the COG.
    Mg is gravitation force acting on the center of mass, which I have broken into Mgx and Mgy (rather than throwing around sines and cosines )


    The sum of moments around the tire contact patch are zero at the time right before front tire lift, so
    M clockwise = M counterclockwise

    The clockwise moment is:

    Mgy (A)

    The counterclockwise moment is the sum of the moment caused by the drive force and that of gravity pulling the weight at the COG backward:

    Mgx (B) + F(B)

    The point of all this is to see what happens if you move the COG upward. distance A stays the same and distance B becomes greater at COG 2. So the counterclockwise moment becomes greater, and the wheel is more likely to lift.

    The only way to counter that lift from the higher COG is to also move it forward, so that the clockwise moment again balances the counterclockwise moment.

    One issue we need to agree on before we proceed, is the location of the fulcrum that the bike rotates around when the front wheel lifts off the ground. You have Identified it as the rear tire contact patch but may I suggest that it is in fact the rear axle. The reason being is that front lifts off the ground the rear tire does not rotate backwards but caries on moving forward. Wheel axles have a unique property in that unless they fall sideways they cannot be forced nearer to the ground. Also a tire surface rotating makes for a complicated form of fulcrum.

  3. #178
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    Quote Originally Posted by GrahamWallace View Post


    One issue we need to agree on before we proceed, is the location of the fulcrum that the bike rotates around when the front wheel lifts off the ground. You have Identified it as the rear tire contact patch but may I suggest that it is in fact the rear axle. The reason being is that front lifts off the ground the rear tire does not rotate backwards but caries on moving forward. Wheel axles have a unique property in that unless they fall sideways they cannot be forced nearer to the ground. Also a tire surface rotating makes for a complicated form of fulcrum.
    Yes I was pondering that very point. I have seen the analysis done both ways, and I'm not sure which is more correct. I can see the argument for using the rear axle rather than the tire contact patch as the fulcrum. Doing it this way, I don't think anything changes in the analysis I posted. Distance B becomes shorter (by the radius of the wheel), and distance A stays the same.

  4. #179
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    Quote Originally Posted by meltingfeather View Post
    I don't get why you are splitting the force out of the torque or what the justification for doing so. Equal and opposite means the torque reaction is the same as the applied torque...
    If the torque is say coming from a motor that is driving a wheel. And the casing of the motor is anchored to a lever, then the measurement of the torque reaction will depend on where along the lever you measure it. Only if you measure it at a point along the lever which is equal to the radius of the wheel will it be of the same magnitude.

    [QUOTE=meltingfeather;9737919
    Again, in your own example of COG at infinity the bike tips immediately upon input and you acknowledge this. How is that not a direct contradiction to your argument?
    [/QUOTE]
    I did indeed acknowledge that the inertia of the CoG at infinity would cause the bike to tip.
    (See Weight transfer - Wikipedia, the free encyclopedia for the reason why?)
    But in theory if the CoG was neither accelerating nor decelerating but traveling at a constant velocity there would be no force present to tip it. Of course traveling at a constant velocity on a bicycle up a steep hill is impossible, because of the pulsed nature of the drivetrain.


    [QUOTE=meltingfeather;9737919
    It started for me when you said that raising COG equalizes weight distribution between the wheels, something I still dispute and which is very easily proven false.
    I don't think we're going to get anywhere, but it's been a pleasure. [/QUOTE]

    For my part I am gaining insights and understanding that I would have not without having this discussion.

    Namely that what I refer to as CoG inertia more commonly known to motorsport enthusiasts as "axle weight-shift" is not the same phenomenon to torque reaction.

    On a bicycle weight shift is only caused by acceleration and deceleration.
    "So you can avoid the issues it creates by keeping your speed steady".

    Torque reaction is created whenever there is torque present in a system.
    It is unavoidable even in constant velocity situations.

    Therefore an electric powered mountain bike should be able to climb steeper slopes because of its smooth power delivery and ability to travel with constant velocity.
    Moving the center of mass upwards on such a machine would reduce the upwards leverage of the torque reaction trying to lift the front wheel, without raking any weight off the rear wheel.

    The next question is could a pedaled bicycle be made that had a torque delivery as smooth as an electric motor? Because if it could be made, such a bike should be able to climb slopes as steep as the Segway.

  5. #180
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    Quote Originally Posted by GrahamWallace View Post
    ...
    One issue we need to agree on before we proceed, is the location of the fulcrum that the bike rotates around when the front wheel lifts off the ground. You have Identified it as the rear tire contact patch but may I suggest that it is in fact the rear axle. The reason being is that front lifts off the ground the rear tire does not rotate backwards but caries on moving forward. Wheel axles have a unique property in that unless they fall sideways they cannot be forced nearer to the ground. Also a tire surface rotating makes for a complicated form of fulcrum.
    If I could butt in here with two questions...

    What happens when your COG falls in front of the rear axle, but behind the tyre contact patch?

    Assuming a constant pedaling speed, what happens to the forward velocity of the rear wheel once the bike starts rotating backwards?

    I believe that, in a simple model, the fulcrum is the tyre contact patch.
    Last edited by sbitw; 10-01-2012 at 10:34 PM. Reason: Clarification

  6. #181
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    Quote Originally Posted by GrahamWallace View Post
    If the torque is say coming from a motor that is driving a wheel. And the casing of the motor is anchored to a lever, then the measurement of the torque reaction will depend on where along the lever you measure it. Only if you measure it at a point along the lever which is equal to the radius of the wheel will it be of the same magnitude.
    I get more of what you're saying after thinking about it a bit more.
    However, you are saying "equal and opposite" and then turning around and saying the torque reaction depends on distance from the pivot. It does not. Equal and opposite is valid, the mechanism by which the force component of the torque reaction is reduced is the lengthening of the lever arm, which multiplies the force from a torque perspective. Since the mass stays the same in this case, I can see what you are talking about, but think the effect is negligible. You have been talking about torque reactions at constant velocity, which requires only enough torque to counter drag. Weight shift, especially on grade and with a pulsed drive, I think is much more of a driver, and raising the COG is detrimental in that case.
    Quote Originally Posted by GrahamWallace View Post
    For my part I am gaining insights and understanding that I would have not without having this discussion.
    Me too. I thought we had reached an impasse, which I didn't understand, since you seem to be a logical and educated fellow, so I gave it a bit more thought and I think I was looking past torque reactions to what I think is more of an effect.

    Quote Originally Posted by GrahamWallace View Post
    Namely that what I refer to as CoG inertia more commonly known to motorsport enthusiasts as "axle weight-shift" is not the same phenomenon to torque reaction.
    I get it now.

    Quote Originally Posted by GrahamWallace View Post
    On a bicycle weight shift is only caused by acceleration and deceleration.
    "So you can avoid the issues it creates by keeping your speed steady".
    It is also caused by grade. Changing the angle of incline of the bike has the same effect as summing the vertical weight vector with the horizontal one that results from acceleration on level ground.

    Quote Originally Posted by GrahamWallace View Post
    Torque reaction is created whenever there is torque present in a system.
    It is unavoidable even in constant velocity situations.
    I agree.

    Quote Originally Posted by GrahamWallace View Post
    Therefore an electric powered mountain bike should be able to climb steeper slopes because of its smooth power delivery and ability to travel with constant velocity.
    Moving the center of mass upwards on such a machine would reduce the upwards leverage of the torque reaction trying to lift the front wheel, without raking any weight off the rear wheel.
    This is impossible. The sum of the ground reactions at the two contact patches must equal the mass of the bike+rider.
    Like a weight distributing trailer hitch, the introduction of the moment causes a skew in the distribution, but not a difference in the sum of the ground reactions.
    Quote Originally Posted by GrahamWallace View Post
    The next question is could a pedaled bicycle be made that had a torque delivery as smooth as an electric motor? Because if it could be made, such a bike should be able to climb slopes as steep as the Segway.
    Sure... pedal it with a robot.
    Last edited by meltingfeather; 10-01-2012 at 09:00 PM.
    Quote Originally Posted by pvd
    Time to stop believing the hype and start doing some science.
    29er Tire Weight Database

  7. #182
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    Wow the numbers and calculations in this thread are too much. You can spin it any way you want but the modern 700c Mt. Bike was based on the advent of the "tire". It created a market for high volume, low pressure tires that has gained an enormous following, won World Cups and Olympic Gold Medals as well as use on thousands of bikes that just plain old people ride in all sorts of ways and places all over the world. Not just some boggy glen in the British Isles.

    Here is a photo of a bike with Hakkapaleta's on it:

    Cleland: The original big wheeled off-road bicycle?-image.jpg


    While it may be close to the same height it lacks the volume and that folks is what made me subscribe back in 99'.

    For some reason my iPad won't allow me to post multiple pics as I was going to insert one of a "tire" for reference but just go look at what you have on your bike. Not a huge difference but big enough to make a difference.

    I would venture to say that the new Knard tire is an equal step above and I can't wait to give them a go. Life is incremental and that is what keeps it interesting. Innovation is key, not mucking about trying to figure out which came first, the chicken or the egg.
    A bike by any other name is still a bike.

  8. #183
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    Cleland: The original big wheeled off-road bicycle?-image.jpg
    A bike by any other name is still a bike.

  9. #184
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    Quote Originally Posted by sbitw View Post
    If I could butt in here with two questions...

    What happens when your COG falls in front of the rear axle, but behind the tyre contact patch?
    Hi sbitw,

    That's an interesting question. In my logic it depends where you believe the fulcrum is. If it is the axle then the CoG is still creating a small downwards moment of rotation even though it is directly above the contact point. If the contact point is the fulcrum then there will be no moment of rotation so the front wheel must lift. This will happen even when the bike is moving forward at a constant speed and there is no forces pushing the CoG backwards as the torque reaction alone will lift the front wheel. The front wheel accelerates as it lifts, the energy required for this is stolen from the torque of the rear wheel. But not enough energy will be required to stop the rear wheel from rotating forwards. If pedaling continues then the bike will continue to accelerate in its rotation around the axle but with gravity now assisting the back flip where earlier on it was resisting it.

    For the rear contact patch to be acting as the fulcrum the wheel would have to rotate backwards whilst its brake was applied.

    Quote Originally Posted by sbitw View Post
    Assuming a constant pedaling speed, what happens to the forward velocity of the rear wheel once the bike starts rotating backwards?
    The torque of the rear will be split between moving the bike forward and lifting the front end so the rear wheel must lose some forwards velocity.

    Quote Originally Posted by sbitw View Post
    I believe that, in a simple model, the fulcrum is the tyre contact patch.
    There may be an error in my reasoning,
    If there is, I am hoping that someone will spot it and point it out.

  10. #185
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    Quote Originally Posted by Bigwheel View Post
    Click image for larger version. 

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    Tucson Mountain Park?

  11. #186
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    Quote Originally Posted by GrahamWallace View Post
    1999 WTB Nanoraptor dimensions: Otherwise known as "the tire"

    700x52c (marked size)
    A 700c rim diameter is 622mm add 52mm x 2 for the additional diameter of the tire to get an overall diameter of 726mm or 28.5826771653852 inches.

    So it appears that the worlds first 29er tire only measures 29inches when rounded up to the next integer.

    In Comparison:
    Nokia Hakkapeliitta snow tire dimensions
    (The tire used by Geoff Apps on his 1981 700c rimmed Cleland)

    700x47c (marked size)
    A 700c rim diameter is 622mm add 47mm x 2 for the additional diameter of the tire to get an overall diameter of 716mm or 28.188976377983202 inches.

    That makes the Nokia 10mm or 1.4% smaller in diameter

    A crucial difference?

    From the Cleland viewpoint it means 5mm more mud clearance.

    Quote Originally Posted by Bigwheel View Post
    WYou can spin it any way you want but the modern 700c Mt. Bike was based on the advent of the "tire". It created a market for high volume, low pressure tires that has gained an enormous following, won World Cups and Olympic Gold Medals as well as use on thousands of bikes that just plain old people ride in all sorts of ways and places all over the world. Not just some boggy glen in the British Isles.
    But there were a string of events that led to the "tire",
    Cleland: The original big wheeled off-road bicycle?-hakkapeliitta014.jpg

    Quote Originally Posted by Bigwheel View Post
    While it may be close to the same height it lacks the volume and that folks is what made me subscribe back in 99'.
    I agree.

    Quote Originally Posted by Bigwheel View Post
    For some reason my iPad won't allow me to post multiple pics as I was going to insert one of a "tire" for reference but just go look at what you have on your bike. Not a huge difference but big enough to make a difference.
    The picture you show is not a 700x47c Nokia Hakkaoeliitta. Here is picture of one like those Geoff Apps exported to the US in the 1980's:
    Cleland: The original big wheeled off-road bicycle?-1981-cleland-aventura-700c-x-47-hakkapelliita-tires-finland.jpg
    And Here is a picture of a 1988 Bruce Gordon 700c "Rock N Road" tire. The tire that inspired Wes Williams, who with Garry Fisher commissioned the Nano-raptor. Notice that the tread pattern was copied from the Hakkapeliitta.
    Cleland: The original big wheeled off-road bicycle?-1988-bruce-gordon-rock-n-road-tire.jpg

  12. #187
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    Quote Originally Posted by GrahamWallace View Post
    The force that acts on the bike below the center of gravity does indeed create a moment but only when drive forces try to accelerate the CoG. These are what I call inertia forces/reaction forces but I believe that they are more commonly called weight transfer or load transfer forces.
    Weight transfer - Wikipedia, the free encyclopedia
    I think the torque reaction you keep talking about is the moment caused by the force pushing the bike forward. At constant velocity, this force is balanced with gravity and friction holding it back. Balanced forces, no net moment. When accelerating this force is larger than the counteracting forces. This creates a total moment about the COG. I don't think there is any other torque.

    Weight transfer forces are similar but distinct from torque reaction forces in that they are only present in cases of acceleration or deceleration. Therefore, they do not apply to a Segway when it is climbing at a constant velocity. Torque reaction however, occurs whenever torque is present. For instance if you clamped the rear wheel of an electric bicycle to the floor and then started the motor in a low gear the front wheel would lift into the air even if the bicycle does not move forwards.
    I can't picture the configuration of your electric bike, but if I clamp the rear wheel of a regular bike and step on the crank, the front end will not rise.

    Why does the bike have to be electric, and how does that change things? If an electric motor shaft is attached directly to the bottom bracket spindle, motor torque is converted to chain tension. Chain tension is converted to force on the rear cog. Since the wheel is clamped, there is no motion. No torque can be transmitted from the wheel to frame because the wheel is attached to the frame only by the axle with ball bearings. Only linear force can transfer from wheel to frame. You can't transfer a torque through a pivot point.

    When I went to school, the free body diagram would identify all forces and moments in the system. This torque reaction you are talking about seems to be something not identified in the drawing I made? Then where does it come from, where is it applied, and where is the force that generates it?
    Last edited by smilinsteve; 10-02-2012 at 11:38 AM.

  13. #188
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    Quote Originally Posted by Originally Posted by GrahamWallace
    Torque reaction is created whenever there is torque present in a system.
    It is unavoidable even in constant velocity situations.
    Quote Originally Posted by Meltingfeather
    I agree.

    I disagree. Is this the heart of the matter here?

    Newtons third law does not state that every torque creates an equal and opposite torque.

    Torque is just a force that creates rotational motion. That force could have a reaction that creates no rotational motion.

    Example:

    Force from your leg > torque at bottom bracket > Tension on chain > torque at wheel hub > force from tire on ground > equal and opposite reaction is linear force on wheel axle pushing bike forward.

    See how forces convert to torques which convert back to linear force?
    Forces have reactions. Forces can cause torque, or not. Torque can be converted to linear force with no equal and opposite torque.

    Example 2:

    Take your bike as above. Pin one end of the chain to your chainring. The other end of the chain is not attached to your wheel, but to the center of a wooden box sitting on the road.
    Push down on the crank;

    Force from leg > torque on bottom bracket > tension in chain > Linear motion of box.

    Example 3

    Same as example 2 but chain is attached to the top of a tall skinny box with high coefficient of friction between the box and the ground;

    Force from leg > torque on BB > tension on chain > torque on box, causing it to fall over.

    The difference between example 2 and 3 is whether or not the force from the chain acts through the COG. In example 3 it doesn't, and creates a torque.


    I guess what I'm getting at here Graham, is that if there is a "torque reaction" at the center of gravity of the rider, then it is caused by some force acting a distance away from the COG.

    I see the torque from pedaling creating a ground force below the COG that creates a moment about it.
    You seem to think there is another source for torque around the COG, but I don't see it.

  14. #189
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    Quote Originally Posted by smilinsteve View Post
    I think the torque reaction you keep talking about is the moment caused by the force pushing the bike forward. At constant velocity, this force is balanced with gravity and friction holding it back. Balanced forces, no net moment. When accelerating this force is larger than the counteracting forces. This creates a total moment about the COG. I don't think there is any other torque.

    Anything that rotates clockwise will create an anti-clockwise reaction. If you sit in a revolving chair, hold your arms outwards and then move them quickly clockwise, your body and the chair will rotate anti-clockwise as a reaction to the torque generated by the moving arms. Likewise if a bicycle wheel rotates clockwise there will be an anti-clockwise reaction in the frame.

    Quote Originally Posted by smilinsteve View Post
    I can't picture the configuration of your electric bike, but if I clamp the rear wheel of a regular bike and step on the crank, the front end will not rise.
    It may if you put it in a low gear, and definitely would if you placed the bike on a steep incline.

    Quote Originally Posted by smilinsteve View Post
    Why does the bike have to be electric, and how does that change things? If an electric motor shaft is attached directly to the bottom bracket spindle, motor torque is converted to chain tension. Chain tension is converted to force on the rear cog. Since the wheel is clamped, there is no motion. No torque can be transmitted from the wheel to frame because the wheel is attached to the frame only by the axle with ball bearings. Only linear force can transfer from wheel to frame. You can't transfer a torque through a pivot point.
    There is also an axle and ball bearing connection between a revolving chair and its base but it can still be made to rotate without you touching anything around you.

    Quote Originally Posted by smilinsteve View Post
    When I went to school, the free body diagram would identify all forces and moments in the system. This torque reaction you are talking about seems to be something not identified in the drawing I made? Then where does it come from, where is it applied, and where is the force that generates it?
    1/ It comes from the rear wheel torque.
    2/ It is applied to anything that stops it from moving freely.
    3/ My legs and feet and then the mechanical advantage is increased via low gearing.

  15. #190
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    Quote Originally Posted by smilinsteve View Post
    I disagree. Is this the heart of the matter here?
    I'm not sure.
    Quote Originally Posted by smilinsteve View Post
    Newtons third law does not state that every torque creates an equal and opposite torque.
    But they do. This is the basis for the sum of moments analytical tool in statics.

    Quote Originally Posted by smilinsteve View Post
    Torque is just a force that creates rotational motion. That force could have a reaction that creates no rotational motion.
    I do not believe it can.

    Quote Originally Posted by smilinsteve View Post
    Example:

    Force from your leg > torque at bottom bracket > Tension on chain > torque at wheel hub > force from tire on ground > equal and opposite reaction is linear force on wheel axle pushing bike forward.

    See how forces convert to torques which convert back to linear force?
    Forces have reactions. Forces can cause torque, or not. Torque can be converted to linear force with no equal and opposite torque.
    You took one force and translated it through at least four different bodies to arrive at your conclusion, which I'd say is a little larger in scope than what Newton intended.
    The reactions are between the individual bodies, not translated through a machine. The equal and opposite force from tire on ground is ground on tire. Likewise for every piece in your example.
    Quote Originally Posted by pvd
    Time to stop believing the hype and start doing some science.
    29er Tire Weight Database

  16. #191
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    I will try and explain torque reaction a different way.

    If you constrain a large force it will try and find anyway it can to break free.

    If you constrain the torque force in a rear wheel by giving it a large amount of resistance from the ground, then it will look for other places to escape. It could break the chain for instance, or it could cause the front wheel to lift off the ground. And the bicycle doesn't even need to move for this to happen.

    Newtons third Law refers to forces. All forces.

    They can be restrained and not visible like the tension in a chain.
    The same is true for reaction forces. But sometimes they find ways to unexpectedly break free.

    If torque reaction does not exist why invent "Torque Reaction Arms" ?
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    BMF Torque Wrench Co. - Model SD Wrenches
    Last edited by GrahamWallace; 10-02-2012 at 12:36 PM. Reason: Typos & add picture

  17. #192
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    Quote Originally Posted by meltingfeather
    You took one force and translated it through at least four different bodies to arrive at your conclusion, which I'd say is a little larger in scope than what Newton intended.
    The reactions are between the individual bodies, not translated through a machine. The equal and opposite force from tire on ground is ground on tire. Likewise for every piece in your example.
    Well, I'm thinking the action reaction pairs newton talked about are forces. Forces can create torque or not. So in my example, how would you break down the action reaction pairs?

    Force on pedal creates an opposite force from pedal to foot!
    In this case, it doesn't matter if that force from foot to pedal creates a torque or doesn't, but it does.

    In my example of the chain attached to the top of the box, the reaction to the force on the box by the chain is the force on the chain by the box. the chain creates a moment that topples the box, but what is the "torque reaction?" there doesn't need to be an equal and opposite torque, only an equal and opposite force.

  18. #193
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    Originally Posted by smilinsteve
    Newtons third law does not state that every torque creates an equal and opposite torque.
    Quote Originally Posted by meltingfeather
    But they do. This is the basis for the sum of moments analytical tool in statics.
    In statics, if a body isn't rotating, you know there is no net moment on it.

    But what does that have to do with bodys that are rotating? If I am in outer space and push on one end of an asteroid floting freely, the equal and opposite reaction to my push on the asteroid is a force against my hand. So I move backwards, and the asteroid starts rotating. So my push created a torque, but the equal and opposite reaction was a linear force against me causing me to move, not rotate.

  19. #194
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    This is going to be my last post to you Graham but let me say this. Stick to the things you know about what led Geoff to using 700c "off trail" and don't pretend to know what led Wes to his part in the "tire" or Gary Fisher either because you obviously don't.

    And btw, that pic of the tacoed wheel in your reply to my last post was probably not the best way to illustrate your point.
    A bike by any other name is still a bike.

  20. #195
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    Quote Originally Posted by smilinsteve View Post
    In statics, if a body isn't rotating, you know there is no net moment on it.

    But what does that have to do with bodys that are rotating? If I am in outer space and push on one end of an asteroid floting freely, the equal and opposite reaction to my push on the asteroid is a force against my hand. So I move backwards, and the asteroid starts rotating. So my push created a torque, but the equal and opposite reaction was a linear force against me causing me to move, not rotate.
    You could also push the asteroid in away that makes you rotate.It depends on where in your body the push originates relative to your center of mass.

  21. #196
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    There is also an axle and ball bearing connection between a revolving chair and its base but it can still be made to rotate without you touching anything around you
    In your swivel chair example the chair is analagous to the wheel and the base of the chair is analagous to the frame. You can spin that chair all you want, but you aren't going to transmit any torque to the base.

    It may if you put it in a low gear, and definitely would if you placed the bike on a steep incline.
    Your bike with the clamped wheel is an easy experiment to do at home, so lets do that and see what happens. I am sure you can not lift the front end of the bike. Draw a free body diagram and show the force that lifts the bike. ?
    If the rear wheel is clamped, say by a rear disc brake, the force on the crank creates internal forces in the frame transmitted from crank to chain to axle, and from brake rotor to caliper to frame, etc. There is no force between the bike and ground.
    Internal forces can not cause motion. Its like trying to grab the arms of your chair and lifting yourself off the ground while you are sitting it

  22. #197
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    If torque reaction does not exist why invent "Torque Reaction Arms" ?
    I already mentioned nut drivers as one example of a torque reaction. I don't see the analogy to a rider pedaling uphill.

    Again, a free body diagram, like I posted, is the way you analyse the forces and moments in a system.
    The way to do this problem is to evaluate the moments at the point of tire lift. I already showed the effect of moving the COG upward.

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    Quote Originally Posted by Bigwheel View Post
    This is going to be my last post to you Graham but let me say this. Stick to the things you know about what led Geoff to using 700c "off trail" and don't pretend to know what led Wes to his part in the "tire" or Gary Fisher either because you obviously don't.
    But I would like to know where I have gone wrong?

    Quote Originally Posted by Bigwheel View Post
    And btw, that pic of the tacoed wheel in your reply to my last post was probably not the best way to illustrate your point.
    Is a prototype that is 30years before its time not allowed a few teething troubles?

    Here is an independent view of 29er history:
    Guitar Ted Productions: The Beginnings Of The Modern 29"er: A History
    Last edited by GrahamWallace; 10-02-2012 at 02:58 PM. Reason: To add a link

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    Quote Originally Posted by GrahamWallace View Post
    You could also push the asteroid in away that makes you rotate.It depends on where in your body the push originates relative to your center of mass.
    Agreed, but I am trying to disprove what you said, that any system with a torque must have a torque reaction.

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    Quote Originally Posted by smilinsteve View Post
    Agreed, but I am trying to disprove what you said, that any system with a torque must have a torque reaction.
    And you have, and are right in pointing out that a force can be turned into a torque and a torque into a force.

    Now you need to find a stationary swivel chair, lift your feet off the floor, introduce some torque by waving your arms and legs and see if the chair rotates.

    Or failing that explain why a hovering helicopter needs a tail rotor?

    Or failing that research the difference between a torque reaction arm and a nut driver.

    Or drill a hole in a wall and see if the electric drill tries to rotate the opposite way to the bit.

    If Newton had meant that only a linear force has an equal and opposite reaction. Would not he have said so?

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