Bicycle

https://www.youtube.com/watch?v=9cNmUNHSBac

https://en.m.wikipedia.org/wiki/Target_fixation

Any practical outcomes for hobby wheelbuilders with conventional parts (like some sort of novel lacing pattern or something like that)?

I was shopping for a kids carrying bikes, called bakfiets[1] (I think) in the Netherlands. The salesperson offered me a trial ride, his advice is something I still remember. Don't bother about the front wheels (they are far out in front), just look where you want to go and your hands will take care of steering and balancing.

[1] https://www.bakfiets.com

Edit: fixed thanks to the correction by “isoprophlex”!

Higher the velocity, the larger the arc required.

I forget completely where I might have read or heard this, but I love it so much I'm going to keep telling it. Can anyone confirm?

The way I try to avoid this is to remind myself that knowing the name of something is not knowing about something, only about the existence of that something.

There are lots of things I know the names of, but relatively few things I actually know about.

The classic example is asking people to describe the process that causes the phases of the moon. Most (myself included the first time) describe an eclipse, which is wrong.

At one stage Klein had a problem with the chainstays separating at the bottom bracket and a number of people rode those bikes after breaking them... almost exactly the "missing chainstay" problem above.

I've built some very weird bicycles and broken both those and conventional bicycles. I have at least some idea of what works... I'd be willing to build as many of those renders as someone was willing to pay for.

Random things off the top of my head: Some time ago they built a self-propelled helicopter, which also used bike technology (gears etc). I vaguely recall that people did state that rowing is what you should use to get the most energy out of a human body - it is (or can be) a full-body motion, including the large muscles in the back and legs and the smaller ones in the arms, while cycling mainly uses the legs. But the mechanism to translate rowing energy into the propellers was too heavy, or something like that.

Actually it might have been a HN thread. Here's one from 10 years ago, and it just so happens that I had made my account by then so this was probably it: https://news.ycombinator.com/item?id=6028326

See:

https://en.wikipedia.org/wiki/MacCready_Gossamer_Condor https://en.wikipedia.org/wiki/MacCready_Gossamer_Albatross https://en.wikipedia.org/wiki/MIT_Daedalus https://en.wikipedia.org/wiki/AeroVelo_Atlas https://en.wikipedia.org/wiki/Hydrocycle

Riding a bike is most efficient at a certain speed and becomes less efficient very quickly as you get faster. So when I mean 9-10 times more efficient, I mean a person walking at a comfortable speed vs cyclist riding at a comfortable speed (on relatively level asphalt road).

https://www.youtube.com/watch?v=ob_GX50Za6c

https://www.themarginalian.org/2011/12/21/steve-jobs-bicycle...

(And internal combustion engines; how are you going to distribute them around the Roman Empire by the tens of millions without trucks or ships?)

The invention of the bicycle came at a similar time like engine driven vehicles. Before those became popular, the direct competitor for bicycles (one person transportation) were horses.

There might have literally not been a need to invent a bicycle as horses fulfilled the same purpose and had the advantage that they fared better on the back then nearly non-existent infrastructure.

Also: a single person transportation vehicle was not something a lot of people needed in their lives. You needed something to move stuff, but the demand to move single people daily came into existence with the dawn of big cities.

Yeah they could produce small items - but to make the steel of the quality needed for bicycles is pretty new - the past 150-200 years with the Bessemer process

A bike at any other point in human history would have been completely useless trying to traverse natural terrain.

Very strange. I get that we take things for granted if they've been around forever (ie. since before we were born). But I never considered bicycles "primitive". What makes you think that? Is it because they don't need electronics? What is a non-primitive transport technology?

He settles on general economic and cultural factors. Experimentation requires there to be enough people with spare time and resources to play around with things with no immediately obvious payback.

https://en.wikipedia.org/wiki/Countersteering

There should be a central repo for all subjects where topics can be looked up to find a guide like this one - and the prompt is public, with revision edit logs (like wikipedia) such that a standard agreed upon response can be adopted by acedmia for explaining a particle concept.

Let the acedemics expand upon, tangent from, deep dive into the sub components of each topic.

The University.ai

I am not saying people don't countersteer, only that it isn't necessary to make a turn.

Also, bicycles aren't motorcycles where the weight ratio between rider and vehicle is swapped.

If you don't feel like clamping your handlebars so they only turn one direction, try this: coast along a straight line (and outdoor basketball court is great). Then pick a direction and just lean that way. You can absolutely keep your wheels on the line until you turn in the direction you picked, with no countersteering necessary.

This "fact" came about with a video of low skill riders who can't manipulate a bike very well, or don't know what it is they're doing when they do it.

If the cyclist is vegan or even an average diet, yes. If the cyclist is paleo, a Prius with 2-person occupancy may actually be more carbon-efficient:

https://keith.seas.harvard.edu/blog/climate-impacts-biking-v...

...On flat smooth surfaces. On any natural environment or terrain they are nowhere near as efficient as walking.

Forces don't "split" that way. 100% of the force goes into creating linear acceleration, and 100% of the force goes into creating torque.

> This would appear to violate the conservation of energy.

It's not. The off-center force does more work, putting more energy into rotation.

First, there is no splitting between linear momentum and angular momentum per se. They have different units, you can't add them, and it makes no sense to say "this is 30% linear momentum and 70% angular momentum". But you can calculate how much energy is stored in linear motion and how much is stored in angular motion, and (at least at non-relativistic speeds), you can indeed add them. So you are on to something here.

But Newton's Laws don't lie. If you apply a force F, then a=m/F, and the fact that the object is spinning doesn't change the acceleration. Yet applying the force off-center does indeed seem to add more energy to the object: you're accelerating it just as much as if you applied the force on-center and you're also spinning it.

So how do you resolve this? A piece of general advice in physics (and math, and many other fields) is to state your assumptions and your questions precisely and unambiguously. The question is: if you apply an equal force to two objects of equal mass, and there are no other external forces involved, how can one accelerate faster? But just because the forces are equal doesn't mean that the work (energy applied) is the same. In fact:

W (work) = F (force) * d (distance)

Divide by a small unit of time:

P (power, which is work per unit time) = F * v (velocity, which is distance per unit time)

And that's the velocity of the point that receives the force. And if you look at the animation, you will see that the off-center force on the rotating box is applied to a (variable) spot on the box that is moving to the right. So the power needed to apply the force is larger, and more work is done.

(In fact, the excess velocity is ωr, so the excess power is Fωr = ωτ (angular velocity times torque), which is exactly the power needed to produce angular acceleration. So energy is conserved and all is well.)

Some of its wisdom:

  “The gross and net result of it is that people who spent most of their natural lives riding iron bicycles over the rocky roadsteads of this parish get their personalities mixed up with the personalities of their bicycle as a result of the interchanging of the atoms of each of them and you would be surprised at the number of people in these parts who are nearly half people and half bicycles...when a man lets things go so far that he is more than half a bicycle, you will not see him so much because he spends a lot of his time leaning with one elbow on walls or standing propped by one foot at kerbstones.”

He has some hints on wheel adjustment (after describing building)

https://www.sheldonbrown.com/wheelbuild.html

sometimes local bike shops have wheel building classes.

I don't know the answer but will toss out a guess.

I'd speculate one of the biggest differences is how each bike is used and its intended design based on that use case. Centrifugal forces combined with traction of tire to surface will be very different between road bike tires at high speed on pavement versus mountain bike tire and low/moderate speeds on dirt. Beyond that, a mountain bike is often rode through technical terrain that requires dynamic balance by the rider (rider strategically shifts weight over bike) - whereas road bikes appear to be rode with a more "static" balance between rider and bike.

2. Has to do with geometry and thickness of the tires.

To generalize the article even more, the way a bike turns is like this: for a given speed and radius through a corner, there is a necessary lean angle. That lean angle determines the camber thrust of the tires, which is the centripetal force that makes the bike turn. However, you also have to make the bike yaw, which means the front has to generate a greater sideways force than the rear. This is accomplished through adding steering angle to the front tire. The longer the bike is, the greater the difference that is needed between front and rear sideways forces.

Furthermore, the steering angle of the front tire is affected by the head angle (90-rake angle), and geometric trail (caster effect). The greater the geometric trail is, the more the tire wants to resist turning. The greater the speed, the higher this effect. Conversely, the slacker the head angle is (lower in value, greater rake angle), the more the front tire wants to turn into the turn (because the wheel axle lower in height with increasing steering angle).

The reason why you generally lean the mountain bikes under you are 2 fold. First, the bikes are longer, so naturally you need the greater difference, which means you need more force from the front. You would exceed the max slip angle of the front tire if you stayed upright, especially on looser dirt. So instead, you lean the bike more to engage camber thrust. Secondly, the tires on mountainbikes are designed with side knobs specifically for cornering, so you want to engage those knobs.

The opposite problem exists on street motorcycles, where the bikes need to be low enough to the ground to not backflip on acceleration, which limits the available bike lean angle. So instead, riders learn to hang off the bike. This in turn requires the front end to be turned more. As a consequence of this, bikes understeer or oversteer behavior is greatly depends on the front end geometry (rake and trail). The trail forces are magnified at the higher speeds, so you need careful tuning of things like fork offsets (which control trail), and rake angle, both of which are affected by suspension moving up and down.

Yet, on supermoto bikes (i.e dirtbikes with street tires, popular in europe), you don't have the ground clearance problem, so you can actually corner them either like street bikes with knee down, or dirt bike style while leaning the bike under you.

I used to do this until recently. It is now a bad habit of mine. On a mountain descent you'll want to steer that road bike how you would a mountain bike by leaning the bike and counter leaning your body. The more gradual the turn and lower thd speed, the less it will matter.