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Ding ding ding! We still don't know how bikes work, we have a pretty good but incomplete model for lift on airplanes, and no one has the faintest why Tylenol wo
by local_issues 3y ago
Ding ding ding! We still don't know how bikes work, we have a pretty good but incomplete model for lift on airplanes, and no one has the faintest why Tylenol works.
We should figure that out! But we can definitely keep using all the applications until then. (Except for Tylenol, we keep learning how bad that stuff is)
EDIT: It won't let me post more, so here's the answers to responses.
For sure!
https://www.cbc.ca/news/science/science-of-cycling-still-mysterious-1.3699012 https://www.cbc.ca/news/science/science-of-cycling-still-mys...
http://www3.eng.cam.ac.uk/~hemh1/gyrobike.htm http://www3.eng.cam.ac.uk/~hemh1/gyrobike.htm
https://www.newscientist.com/article/mg22730370-400-how-does-a-bicycle-stay-upright/ https://www.newscientist.com/article/mg22730370-400-how-does...
It's a fun little fact. We know a ton about BUILDING bikes, which is a more useful tool anyway
- mthomasmw 3y agoDo you have a link handy for "we don't know how bikes work" ?
- prasadjoglekar 3y ago[flagged]
- post-it 3y agoI'm not super interested in watching Joe Rogan and RFK, is there a particular bit where they talk about bikes?
- CSMastermind 3y agoThere's nothing about bicycles in the video he linked.
- post-it 3y agoA classic Freudian clip.
- mensetmanusman 3y agoAmazing choice of word. Always check your clipboard links before pushing send.
- Guthur 3y agoIs it RFKs voice? I find it a little difficult to listen to as well.
- riversflow 3y agoI think that is the wrong link?
- SkyBelow 3y agoI'm assuming they mean the balance mechanism, and specifically what allows us to balance. How much is it the rider shifting their weight, how much is micro steering adjusts as we move forward, how much is the gyroscopic forces of the wheels, how much of it has to do with the angle of the handle bars to the wheel verse the center of weight. That said, I'm guessing this one is well understood by experts, but more complex than someone would assume at first glance, and many who have some understanding likely have an incorrect or at least incomplete understanding of how balancing works.
- BizarroLand 3y agoI wonder what learning the specific system by which bikes are balanced would teach us about the world or human beings? It's such a banal thing to be so fascinating.
- hinkley 3y agoWe don't know until we know. The smart phone is the culmination of understanding a million facts about materials sciences (applied and theoretical), some of which were obvious, some of which were non-obvious. Starting from a transistor you could see from across the room down to ones you can't even see with a magnifying glass.
- doctorwho42 3y agoIt's the reason I got a degree in physics, if you have good professors - discussions like this cause you to break down the problem quite quickly in your head in a working model. Think force diagrams, but with a ton more math backing it up. I actually find the ice skate a better example than a bike. We have all the physics solved for bikes, it's a complicated system but so is everything in motion. Hence we assume a spherical cow for the sake of the problem. But ice skates... Now that's a funky one. Why do ice skates works? Ice skates aren't sharp bladed, they actually have flats. Ice is not slippery, it's when something is on ice in between our shoes and the ice that cause it to be slippery. Some people think it's the localized pressure of the blade that causes ice to locally melt. Hard to really wrap your head around. But it works :)
- hughw 3y agoe.g. What keeps bicycles balanced with or without a rider is still an active area of research, and even the seemingly basic idea that, for a bicycle to be self-stable, it needs to turn the handlebars into the fall, has not yet been proven. [*]https://ciechanow.ski/bicycle/ https://ciechanow.ski/bicycle/
- IshKebab 3y ago"Active area of research" is quite different to "we don't know how they work". We know how they work. We might not have fully characterised the stability conditions, but that's not the same thing.
- hughw 3y agoCmon, man
- salty_biscuits 3y agoYou can write out the equations of motion for a bicycle that will very accurately predict the dynamics. You can put these equations into a numerical simulation and predict motion very accurately. You can change the parameters of the model and do simulations with high confidence. Just because there isn't some neat little equation that says exactly what each parameter change is going to do (without doing the simulation) doesn't mean that we don't understand bicycle physics. It's a silly line of reasoning. Those articles are hyperbolic.
- ddalex 3y agoYou are contradicting yourself: > You can write out the equations of motion for a bicycle > there isn't some neat little equation that says exactly what each parameter change is going to do I mean, if you have the equations you can see what each parameter is doing !
- salty_biscuits 3y ago
- hinkley 3y agoAs a bit of an aside, most people don't know how bicycle wheels work. There's a whole section in https://en.wikipedia.org/wiki/The_Bicycle_Wheel https://en.wikipedia.org/wiki/The_Bicycle_Wheel that talks about how they actually work. It's not tension at the top, it's compression on the bottom.
- denimnerd42 3y agowhat do you mean it's not tension at the top? did you misspeak? bicycle spokes are solely under tensile forces. they can't support compressive forces at all. i'm a hobbyist wheel builder and a once upon a time professional bicycle mechanic during hs & college. if you want to test this take nearly all the pretension out of your spokes and sit on your bike. feel which ones are taught and which ones are completely loose. or just go to walmart. those bikes hardly have any pretension in their wheels.
- bradyd 3y agoThey even make spokes that are rope https://berdspokes.com/pages/technology https://berdspokes.com/pages/technology
- hinkley 3y agoI wonder if those have less or more breakin issues compared to spokes. With a spoke you have to reset the angle of the bend to the shortest distance between the hub and the rim. But with cables they have to settle in along their entire length. Doesn’t change the answer. They’re still compressing. They’re just pretensioned.
- denimnerd42 3y agoyou sound highly confused, what is compressing? the rim? the spoke?
- hinkley 3y ago
- hatsunearu 3y agoYeah, that's complete crap. Bike dynamics is well researched and the instability and stability mechanisms are numerous but well understood.
- ummonk 3y agoNonsense. There's nothing incomplete about our model for lift on airplanes.
- aeternum 3y agoOh really, so why do the Navier-Stokes equations work?
- dkqmduems 3y agoConservation of momentum?
- bandrami 3y agoThere's no a priori reason conservation of momentum would apply; for that matter in 0-angle-of-attack aviation it doesn't. Maybe to put it differently, the "Newtonian" model of flight comes out of assuming CoM applies, which we know isn't universally true. EDITING: of course it always "applies" in the sense that there is a definable system in which total momentum will be unchanged, the point being that there is no guarantee that's a system in which the plane gets lift greater than its weight
- coderenegade 3y agoA symmetrical airfoil at zero angle of attack doesn't generate lift because it doesn't turn the fluid. A non symmetrical airfoil will generate lift even at zero AOA because air has viscosity and the lack of symmetry causes it to turn around the shape. When you bend fluid flow, COM comes into play.
- ummonk 3y agoIf you're asking how to apply the Navier-Stokes equations: apply boundary conditions If you're asking how to derive the Navier-Stokes equations, use continuum / conservation principles.
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- intrasight 3y agoWe don't know how photosynthesis works but we know a ton about GROWING things. And life as we know it depends on photosynthesis.
- MVissers 3y agoI thought we had a pretty good understanding of this up until the molecular and electron level. Am I missing something?
- intrasight 3y agoMy daughter did her research in this field while an undergrad, and explained to me that photosynthesis is not yet well understood. Some of the theories of the mechanism are discussed here: https://physicsworld.com/a/is-photosynthesis-quantum-ish/ https://physicsworld.com/a/is-photosynthesis-quantum-ish/
- dotnet00 3y agoHow photosynthesis works at a cell machinery level is high school level biology.
- intrasight 3y agoThat's not an understanding of how it works
- dotnet00 3y agoI disagree. It very much is an understanding of how photosynthesis works, it isn't a complete understanding sure, but an understanding nonetheless. Unless you're going to argue that we don't know how an MRI works because we don't fully understand the physics behind superconductivity.