Fuckin magnets
How do they work?
this post was submitted on 17 Sep 2024
686 points (98.2% liked)
Greentext
4492 readers
532 users here now
This is a place to share greentexts and witness the confounding life of Anon. If you're new to the Greentext community, think of it as a sort of zoo with Anon as the main attraction.
Be warned:
- Anon is often crazy.
- Anon is often depressed.
- Anon frequently shares thoughts that are immature, offensive, or incomprehensible.
If you find yourself getting angry (or god forbid, agreeing) with something Anon has said, you might be doing it wrong.
founded 1 year ago
MODERATORS
Tide comes in, tide comes out, You can't explain that.
The dumber a civilization is, the more sense God makes.
This pretty accurately describes conservatives.
Gyroscope effect. You ever do the experiment where you spin a bike tire really fast and then try to tilt it? Shit's nuts.
That only causes part of the effect, most of it is the bike's steering countering the momentum of your fall.
You wouldn't be able to balance on a bike with just the wheel spinning, you're too heavy. That is why bikes on those indoor rollers allow the bike to move left and right a bit.
So biking is just falling with style?
Just like orbiting something. Satellites are constantly just falling back to earth, but with enough grace to always miss earth. I bet satellites would be great cyclists!
There is an art, it says, or rather, a knack to flying. The knack lies in learning how to throw yourself at the ground and miss. … Clearly, it is this second part, the missing, which presents the difficulties.
So is walking
load more comments
(1 replies)
load more comments
(2 replies)
Hmmm... Both things involve bicycles... Maybe they're just magic?
The gyroscopic effect of slowly spinning, light bicycle wheels is negligible compared to the weight of the bike and it's rider. If it was what keeps you upright, riding a tiny scooter-thing with skateboard/inliner wheels would be impossible. I mean those without motor, pedals, where you push yourself forward with one foot on the ground), often for kids.
What actually keeps you upright isn't a physical effect, but just training your brain to instinctually keep you upright. While you're moving, turning the handlebar effectively moves the bike below you left and right. So if you start tilting to the right, you turn right (slightly) so the bike/scooter is moving below you to compensate. That's why learning to ride anything that is balancing on 2 wheels takes a relatively long time, but only once. Then your brain knows what to do, and it just works without thinking about it.
The design of the front forks also assists with stability - having some rake and trail means the front wheel has a tendency to self centre (particularly at speed).
load more comments
(2 replies)
Brah just discovered conservation of angular momentum
It's not that. Gyroscopic action exists of course, but it's fairly weak against the weight of your body. Balancing a bicycle is just like balancing an umbrella on your finger, except you can easily move your finger any direction you need. To move the bicycle sideways, you need to already be moving forward.
Track stands! Not a contradiction to your statement at all though: you need to be moving just ever so slightly.
With a fixie it's easy, because you can pedal forwards and backwards in tiny amounts. With a freewheel, it's trickier but you get the hang of it with practice. Ideally you'll have an incline, so you pedal forward to go forward, and ease up to slide back. After some practice I can use the raised reflective paint from e.g. crosswalks as the "incline." This miniscule motion is enough to balance
and like you said, it ain't the angular momentum that does it.
load more comments
(1 replies)
load more comments
(1 replies)
first, and less importantly, your wheels are gyroscopes
second, and much more importantly, at speed you use your steering to compensate for imbalance. You lean a little right? slight steering to the right compensates. When standing still, steering is no longer an option (duh)
load more comments
(3 replies)
It's the central pedal force
my bike doesn’t have a central pedal. how does it stay up right?
Aliens.
load more comments
(3 replies)
Can confirm. Last week, I got home from a ride, stopped in front of the garage, couldn't unclip, and promptly fell over. It turned out one of the bolts fell out from the cleat during the ride, so the cleat just rotated, instead of unclipping. D'oh. Fortunately, I mostly landed in grass, though I did scrape my ankle a bit.
Yeah, I can relate to this...
Same principle as a gyroscope: a turning wheel will tend to stay perpendicular or parallel to the direction of the gravity vector because if it starts tilting away from such orientation there's a force that pushes it back.
Also works better with bigger wheels (if I remember it correctly the effect is related to spinning momentum).
I was pretty surprised when learning Physics and they show us how to derive the formula for that (which I totally forgot since that was over 3 decades ago).
Edit: Actually the gyroscopic effetc is just a part of it. See this article
Actually, it's the bike's geometry rather than a gyroscopic effect. Try rolling a bike backwards rather than forward - it'll topple quickly
Yeah, you're mostly right: Why bycicles stay upright.
There's some gyroscopic effect, but per that article it's not the main reason.
load more comments
(1 replies)
Freestyle BMX riders go in reverse all the time and they don't fall over.
load more comments
(1 replies)
Gyroscopic effect is not even significant. Lock your steering and you will fall over no matter how fast your wheels are spinning. (Which can happen with a badly pitted headset)
Having the pivot point (steering) for the front wheel behind it's axle helps
Yes there are demonstrations on YouTube of bikes just wanting to remain upright. You can role it down a hill and it will self correct. Something to do with physics but I forget the terms.
I'm surprised how much I'm seeing gyro brought up in these comments. It's a factor, but it's practically negligible. It's all in the steering. Start to tip right, and you'll subconsciously steer slightly to the right to correct your balance. Try to ride as slow as you can and you'll find yourself doing these corrections much more frantically and dramatically. The reason for that is because it takes longer for the wheel to roll under your center gravity and "catch" you when you're going slowly so you have to turn in quicker to maintain balance.
Notice that on almost every bike you see, the front axle on the bike is slightly ahead of the neck's axis of rotation. That offset does two things: 1. It stabilizes the steering so that the bike will tend to steer straight and 2. (more important to my point) It makes the balance-correcting effect of steering more immediate and dramatic, making it much easier to ride at slower speeds.
As a counter argument showing why gyro is barely a factor, these exist:
Edit: if you're not seeing the image like I'm not, Google "ski bike".
It's pretty common to bring up gyroscopes for this when people know a little bit about physics. It's all over motorcycle forums, for instance.
As you say, it doesn't work. Experiments have been done where they attach a counter rotating wheel to cancel out the gyroscopic effect, and while it's a little wonky to ride, it works fine.
IIRC, we're not 100% sure how bikes work just yet. Every time somebody comes up with a model that seems to be good, someone finds a counterexample that throws it in the bin. Even your explanation of bike trail isn't all the way there; Razer-type scooters still work without trail on the front wheel.
load more comments
(6 replies)
Dynamic stability
I don’t get it when people (usually chavs) can just sit back with their hands in their pockets - when I try it my handlebars twist out to one side instantly.
load more comments
(2 replies)
What's really hard is getting a 5 year old to understand this before you run out of energy from trying to hold their seat and run at the same time.
That's how I learned it. My dad got tired, let go and stopped.
I noticed it was suddenly much easier to pedal, so I turned around to see him standing 30ft behind me, then I crashed.
load more comments
(2 replies)
load more comments
(1 replies)
If you’ve forgotten high school physics (like me), this is a legitimately strange phenomenon.
Think of this as you inch forward until the green light with a motorcycle behind you. Just stop. Riding at 2 mph is misery.
load more comments
(3 replies)
view more: next ›