Why Do Bycicles Stand Up

[Bryanpoprobson]

Lying here on a sunbed in 37degs, keeping myself amused reading a copy of New Scientist, I have read a comment, referring to a previous article, which I have not referenced. Aparrently scientist are unable to understand the physics behind a Bycicle remaining upright "only" when being riden. Not something I have given much thought to, but it must be something to do with mans bipedal ability to stand upright and the way the brain balances us when walking? I must find the original article and read it! Just wondered if anyone had read it or given it some thought? 

[onebigmonkey]

As a keen cyclist myself, it always amazes me how slowly I can go at traffic lights (the ones I bother to stop at ) and still stay vertical without wobbling.

[bknight]

Lying here on a sunbed in 37degs, keeping myself amused reading a copy of New Scientist, I have read a comment, referring to a previous article, which I have not referenced. Aparrently scientist are unable to understand the physics behind a Bycicle remaining upright "only" when being riden. Not something I have given much thought to, but it must be something to do with mans bipedal ability to stand upright and the way the brain balances us when walking? I must find the original article and read it! Just wondered if anyone had read it or given it some thought? 

A gyroscope phenomena and it shouldn't take much angular motion to observe it.

[Glom]

It's the small, almost imperceptible oscillations in the direction as you cycle that generates the stabilising torque.

Now what happened two weeks ago in Oxhey Park that I'm still showing scars for is something scientists cannot explain. Also, I locked the wheels on gravel.

[smartcooky]

Lying here on a sunbed in 37degs, keeping myself amused reading a copy of New Scientist, I have read a comment, referring to a previous article, which I have not referenced. Apparently scientist are unable to understand the physics behind a Bicycle remaining upright "only" when being ridden. Not something I have given much thought to, but it must be something to do with mans bipedal ability to stand upright and the way the brain balances us when walking? I must find the original article and read it! Just wondered if anyone had read it or given it some thought? 

What???

A scientist doesn't understand the gyroscopic principle? Really? This is the most basic, year 10/10th grade schoolroom physics

ETA;

Here is an excellent video which not only explains that a gyroscope will move at a point 90° around its direction of rotation from where the force is applied, it explains why that happens.

[grmcdorman]

From what I've read, it is not gyroscopic; it's the human correcting balance. If it were truly gyroscopic, then you'd have problems turning which would get worse as you went faster (the turning axis would be equally affected by any gyroscopic effects) - and bicycles without riders would balance. It'd also be easier to balance heavier wheels, and balancing would be much more dependant on speed.

[smartcooky]

From what I've read, it is not gyroscopic; it's the human correcting balance. If it were truly gyroscopic, then you'd have problems turning which would get worse as you went faster (the turning axis would be equally affected by any gyroscopic effects)

Its does get worse as you get faster. Try this experiment.

Ride a bicycle, and once you get some small forward motion, take one hand off and place the other hand on the centre of the handlebars. If you now twist your hand to the right, the bike will veer to the left; this a demonstration of the gyroscopic principle; you are applying a rotational force trying to rotate the wheel to the right, and the wheel reacts 90° in the direction of rotation by tipping to the left.

Cycle faster and you will find you need to apply more force to get the same amount of tipping rection to the left.

- and bicycles without riders would balance. It'd also be easier to balance heavier wheels, and balancing would be much more dependant on speed.

It is easier to balance on heavy wheels, that is part of the reason why a mountain bike is easier to ride than a track racing bike

It is also easier to balance on wheels of a larger diameter when they are spinning and harder when they are not. Again, a clear demonstration that the gyroscopic force is in play.

If you have a nice smooth slope that is, say 15° down, 100m wide (so that there is nothing to hit) and 1000m long, and you give a riderless bike a push down that slope, it will stay upright. It may wobble a bit when the speed is slow, but once the speed builds up, it will stay upright until it hits something or runs out of slope and slows down.

[tikkitakki]

it's the human correcting balance

Human not required.

[smartcooky]

Here is another example of the gyroscopic principle put to work, and when you first see this, it seems counterintuitive.

Anyone who is remotely familiar with helicopters, will know what "cyclic" control sticks are...



..they are the joystick like things in front of each seat that control the roll and and pitch of the helicopter in flight; you push the stick forward, the main rotor tilts forward, and the helicopter tips forward, pulling it back or pushing it left or right tilts the main rotor in the appropriate direction  and the helicopter responds accordingly.

However, what most people do not realise is that the controls are not physically connected that way to the main rotor. On the ground, with the main rotor stationary, if you push and pull the cyclic forwards and backwards, the main rotor will tilt left and right, and likewise if you push the cyclic left and right, the main rotor will tilt forwards and backwards. This is because the cyclic controls are connected 90° out of phase and in advance of the desired resultant force. Also, which way they are connected depends upon which way the main rotor will be rotating, e.g. looking down on the helicopter with the front to the top of the page, if the main rotor rotation is clockwise, and you want to tilt it forwards, the cyclic control must be connected in such a way that when you push it forwards, the control tries to tilt the rotor to the left (tries to push the left side down) so that the resulting gyroscopic force pushes down 90° in the direction of rotation, i.e. the front of the main rotor.

[onebigmonkey]

Interesting.

So would you say that the human correcting balance has more influence on correcting the bike's deviation from a gyroscopic action as we move around in the saddle, shift our weight and generally apply other forces that disrupt it?

[Bryanpoprobson]

Many years ago now I had a bike that had gears in the handlebars I inherited it. I used to challenge people to ride it. It was set up so that if you steered right the wheels would turn left. Even trying to ride 5 meters was impossible for most people. I lost it during one of my house moves but I did manage to master it. There are some street acts that challenge people to ride these bikes for a bet, but I have never found one since I've got the knack ! I live in hope of taking someone's money one day. !

[onebigmonkey]

Many years ago now I had a bike that had gears in the handlebars I inherited it. I used to challenge people to ride it. It was set up so that if you steered right the wheels would turn left. Even trying to ride 5 meters was impossible for most people. I lost it during one of my house moves but I did manage to master it. There are some street acts that challenge people to ride these bikes for a bet, but I have never found one since I've got the knack ! I live in hope of taking someone's money one day. !

Sounds like the famous psychology experiment with the inverted glasses!

[bknight]

It is also easier to balance on wheels of a larger diameter when they are spinning and harder when they are not. Again, a clear demonstration that the gyroscopic force is in play.

Another interesting and informative experiment, take a bicycle wheel and put a handle through the center after spinning the wheel attempt to turn it with you the wheel with your hands and feel the gyroscopic effects resisting changes in attitude

[smartcooky]

Interesting.

So would you say that the human correcting balance has more influence on correcting the bike's deviation from a gyroscopic action as we move around in the saddle, shift our weight and generally apply other forces that disrupt it?

Yes.

Any force that acts on a rotating body in a direction other than along the spin axis will cause a resultant force that will change the direction of the spin axis. That is why the Earth's spin axis rotates through a 25,800 year circle (causing precession of the equinoxes). The gravitational forces of the Moon and Sun exert an uneven force on the Earth due to the fact that it is an oblate spheroid. If the Earth were a perfect sphere, then precession would not happen.