this post was submitted on 17 Sep 2024
695 points (100.0% liked)
Greentext
6193 readers
1241 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 2 years ago
MODERATORS
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)
Which is just regular conservation of momentum plus a force directing it towards some center point it oscillates around, which feels weird because you can hold a lot more of it in your hands than you normally can without that oscillation.
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)
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)
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...
But pedaling on a treadmill make you fall over.
What the hell?
They're called rollers, and they're pretty easy to ride on.
I have heard that it is VERY hard to get started and then very quickly becomes thoughtlessly easy
load more comments
(2 replies)
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.
I figured it was pretty obviously the rider that's making the bike not fall over, not the bike itself.
If the bike's ability to remain upright while moving was a natural feature, then why would you ever need to learn how to ride bikes? You could just sit on it and go if that was the case.
It works on its own. If you push your bike along with a good run and then let go, it'll stay upright until it slows down too much.
Learning to ride a bike is mostly about being confident enough to let the bike work itself out. It gets more stable as it goes faster, but it's natural to be afraid to go faster when it already feels unstable at low speed. Then there's a little bit to learn about countersteering, but most people figure that out without being told it's even a thing.
load more comments
(1 replies)
load more comments
(3 replies)
Dynamic stability
Everyone is wrong. It's the encabulation effect.
Modern bicycles include an isotropic harmonization manifold to achieve the same thing without an encabulator.
load more comments
(3 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)
Real talk, science doesn’t have the answer to this yet.
view more: next ›