What do bikes and bumble bees have in common?

Initialised

Ever wonder how bikes stay up while you're texting in the saddle: So did the boffins and they don't know either.

prj45

My favourite garfield cartoon:

deptfordmarmoset

Whenever I read a sentence like this:

We have found no simple physical explanation equivalent to the mathematical statement that all eigenvalues must have negative real parts

....I need to go for a ride simply to keep my sense of balance

pst88

So what do they have in common? "Scientists" know perfectly well how bees fly.

Confusedboy

All flying creatures do it by falling towards the ground AND MISSING!!! Thank you Terry Pratchett.

bearfraser

it's that mythical !!!!!!!!!!!!!!!!!!! centrifugal force ???

sketchley

Confusedboy wrote:

All flying creatures do it by falling towards the ground AND MISSING!!! Thank you Terry Pratchett.

Ahem - Douglas Adams. HHGTTG part 3.

rhext

Don't know where they found their boffins. Bikes stay upright for the same reason that rolled coins stay upright. It's not gyroscopic stabilisation of the wheels, it's centrifugal forces acting to balance gravity.....

Gravity acts to pull the coin over, so the coin starts to tilt
As it tilts it starts to describe a circle
As it describes a circle, centrifugal forces act on the centre of mass, pushing it upright again.
As it slows down, it needs to describe a tighter and tighter circle in order that centrifugal force continues to balance gravity, until it reaches a point where it's no longer possible and the coin falls over.

Try it!

sketchley

rhext wrote:

Don't know where they found their boffins. Bikes stay upright for the same reason that rolled coins stay upright. It's not gyroscopic stabilisation of the wheels, it's centrifugal forces acting to balance gravity.....

Gravity acts to pull the coin over, so the coin starts to tilt
As it tilts it starts to describe a circle
As it describes a circle, centrifugal forces act on the centre of mass, pushing it upright again.
As it slows down, it needs to describe a tighter and tighter circle in order that centrifugal force continues to balance gravity, until it reaches a point where it's no longer possible and the coin falls over.

Try it!

Make perfect sense that. You need to post that in comments section of the link in the OP.

mudcow007

not connected to bikes but, what type of bees can you get milk from?

Boo bees!!!

rick_chasey

rhext wrote:

Don't know where they found their boffins. Bikes stay upright for the same reason that rolled coins stay upright. It's not gyroscopic stabilisation of the wheels, it's centrifugal forces acting to balance gravity.....

Gravity acts to pull the coin over, so the coin starts to tilt
As it tilts it starts to describe a circle
As it describes a circle, centrifugal forces act on the centre of mass, pushing it upright again.
As it slows down, it needs to describe a tighter and tighter circle in order that centrifugal force continues to balance gravity, until it reaches a point where it's no longer possible and the coin falls over.

Try it!

Don't you mean centripetal?

kelsen

Sketchley wrote:

rhext wrote:

Don't know where they found their boffins. Bikes stay upright for the same reason that rolled coins stay upright. It's not gyroscopic stabilisation of the wheels, it's centrifugal forces acting to balance gravity.....

Gravity acts to pull the coin over, so the coin starts to tilt
As it tilts it starts to describe a circle
As it describes a circle, centrifugal forces act on the centre of mass, pushing it upright again.
As it slows down, it needs to describe a tighter and tighter circle in order that centrifugal force continues to balance gravity, until it reaches a point where it's no longer possible and the coin falls over.

Try it!

Make perfect sense that. You need to post that in comments section of the link in the OP.

Don't do that! You'll destroy any chance of them getting more funding for meaningless experiments.

rhext

Rick Chasey wrote:

rhext wrote:

Don't know where they found their boffins. Bikes stay upright for the same reason that rolled coins stay upright. It's not gyroscopic stabilisation of the wheels, it's centrifugal forces acting to balance gravity.....

Gravity acts to pull the coin over, so the coin starts to tilt
As it tilts it starts to describe a circle
As it describes a circle, centrifugal forces act on the centre of mass, pushing it upright again.
As it slows down, it needs to describe a tighter and tighter circle in order that centrifugal force continues to balance gravity, until it reaches a point where it's no longer possible and the coin falls over.

Try it!

Don't you mean centripetal?

No, I mean centrifugal. Centripetal force is the force you need to exert to hold an object stationary if you're observing from within a rotating reference frame. Centrifugal force is the fictitious force which appears to oppose you while you're trying to do that.....

rick_chasey

Anyway, rhext, your example only covers forces in the vertical direction (i.e. in the direction of gravity), not in the horizontal direction (perpendicular to both gravity and the direction of travel), which is where you need the stability to stop it falling over....

rhext

Rick Chasey wrote:

Anyway, rhext, your example only covers forces in the vertical direction (i.e. in the direction of gravity), not in the horizontal direction (perpendicular to both gravity and the direction of travel), which is where you need the stability to stop it falling over....

Not true: as soon as the coin starts to lean, then a component of the gravitational force will act in the horizontal direction. It's the balancing force exerted by friction on the edge of the coin which causes it to move in a circle in the first place, which in turn leads to the centrifugal force component which balances gravity.

Incidentally, that's why neither coin nor cycle are stable on a frictionless surface....

rhext

Sketchley wrote:

rhext wrote:

Don't know where they found their boffins. Bikes stay upright for the same reason that rolled coins stay upright. It's not gyroscopic stabilisation of the wheels, it's centrifugal forces acting to balance gravity.....

Gravity acts to pull the coin over, so the coin starts to tilt
As it tilts it starts to describe a circle
As it describes a circle, centrifugal forces act on the centre of mass, pushing it upright again.
As it slows down, it needs to describe a tighter and tighter circle in order that centrifugal force continues to balance gravity, until it reaches a point where it's no longer possible and the coin falls over.

Try it!

Make perfect sense that. You need to post that in comments section of the link in the OP.

I'd have to create a login, and I'm not sure I can be bothered. Interesting to note that the 'boffins' are all engineers though. Perhaps they should have asked a Physicist!

rhext

...unless they're trying to answer a subtly different question. Coins are obvious, and it seems intuitive to extrapolate to bicycles. But the centrifugal force explanation doesn't explain why the steering automatically aligns the front wheel exactly with the circle that the bike must describe in order to remain upright.....

shm_uk

Bikes stay upright for exactly the same reason planes stay airborne - the passengers desperately willing the thing to stay upright.

I have not yet managed to create an experiment to prove this though.

In the meantime, you can all pretend it's physics or some such witchcraft.

rjsterry

rhext wrote:

Sketchley wrote:

rhext wrote:

Don't know where they found their boffins. Bikes stay upright for the same reason that rolled coins stay upright. It's not gyroscopic stabilisation of the wheels, it's centrifugal forces acting to balance gravity.....

Gravity acts to pull the coin over, so the coin starts to tilt
As it tilts it starts to describe a circle
As it describes a circle, centrifugal forces act on the centre of mass, pushing it upright again.
As it slows down, it needs to describe a tighter and tighter circle in order that centrifugal force continues to balance gravity, until it reaches a point where it's no longer possible and the coin falls over.

Try it!

Make perfect sense that. You need to post that in comments section of the link in the OP.

I'd have to create a login, and I'm not sure I can be bothered. Interesting to note that the 'boffins' are all engineers though. Perhaps they should have asked a Physicist!

Just a thought, but you don't think they maybe have already considered your explanation, and discounted it for some reason that you may not have considered?

lardboy

Magnets. It's always magnets.

rick_chasey

rhext wrote:

Rick Chasey wrote:

Anyway, rhext, your example only covers forces in the vertical direction (i.e. in the direction of gravity), not in the horizontal direction (perpendicular to both gravity and the direction of travel), which is where you need the stability to stop it falling over....

Not true: as soon as the coin starts to lean, then a component of the gravitational force will act in the horizontal direction. It's the balancing force exerted by friction on the edge of the coin which causes it to move in a circle in the first place, which in turn leads to the centrifugal force component which balances gravity.

Incidentally, that's why neither coin nor cycle are stable on a frictionless surface....

I meant before.

I'm pretty sure it's a centripetal force as soon as it begins to learn - I remember modelling a single motorbike tyre when I studied mechanics and it was pretty straightforward.


Either way, surely anything to do with this explaination is just a form of angular momentum if i remember correctly.

From what I remember learning about one ends up learning about the other anyway.

flimflam_machine

Rick Chasey wrote:

rhext wrote:

Rick Chasey wrote:

Anyway, rhext, your example only covers forces in the vertical direction (i.e. in the direction of gravity), not in the horizontal direction (perpendicular to both gravity and the direction of travel), which is where you need the stability to stop it falling over....

Not true: as soon as the coin starts to lean, then a component of the gravitational force will act in the horizontal direction. It's the balancing force exerted by friction on the edge of the coin which causes it to move in a circle in the first place, which in turn leads to the centrifugal force component which balances gravity.

I meant before.

I'm pretty sure it's a centripetal force as soon as it begins to learn - I remember modelling a single motorbike tyre when I studied mechanics and it was pretty straightforward.

Either way, surely anything to do with this explaination is just a form of angular momentum if i remember correctly.

From what I remember learning about one ends up learning about the other anyway.

Not quite clear on this. Gravity can never act in a horizontal direction since "vertical" is defined as "locally aligned with the gradient of the gravity field, i.e., with the direction of the gravitational force". The reaction force could have a horizontal component but I can't see why it would necessarily have to, it could act entirely vertically through the contact patch.

If a rigid rolling disc leans over why will it start to describe a circle? For a non rigid disc e.g., a wheel with a tyre, one explanation is that the contact patch deforms into a triangle and so it rools like a cone, but a rigid disc like a coin won't deform like that.

Why would a centrifugal force act to push a wheel in a particular direction? Presumably it acts at all points of the rim so it's horizontal component sums to zero.

It's a long time since I've done any physics, christ I feel dim.