Why is balancing on a stationary bike so much more difficult than on a moving one?
In: 48
[removed]
Because all that energy you put into speeding the bike up helps keep it going straight, and that force fights against little wobbles side to side.
When you are stationary, there’s no forward force to fight the side-to-side wobbles, and so instead you have to move your body weight around to counter them.
So the same small tipping forces that make you wobble are always there. But the momentum of the bike does all the work for you fighting against them when the bike is in motion.
have you ever tried balancing say a chopstick upright on your hand? when the chopsitck starts to fall over you move your hand to compensate and get the bottom under the new center of gravity. on a moving bike you can do something similar. when you start to lean into one direction, say left for example, then you can just stear to the left a bit to get the wheels of the bike under the new center of gravity so you dont fall over. usually only very small adjustments are needed, so you dont really notice it though except when people just start to learn to ride bikes.
on a stationary bike you dont have that option and have to balance using some other machanism which is usually harder.
additionally, when the bike is moving your tires are a rotating mass and the gyroscopic effect helps to stabelize the bike. however, i belief this effect to be not as important than the other one i mentioned.
A bicycle is an inverted pendulum. The normal method for keeping it upright is moving the contact point with the ground left or right to keep it underneath the center of mass, and this requires the bicycle to be moving. When the bicycle is moving, it will self-steer in the direction it is leaning, which will help keep it upright(multiple causes for this self-steering effect, including gyroscopic precession, and the geometry of the steering).
When the bicycle is stopped, you can’t move the contact point with the ground enough to stay balanced, so you have to move the center of mass left and right to keep it above the contact point with the ground, this is very hard because the only way you have to move the center of mass left and right is a torque through the contact point, which necessarily causes rotation, so you have to push that even harder so you go back over center in the other direction enough to pull yourself back upright.
When your wheels are in motion, they have momentum, which creates a kind of resisting force to “sideways falling”. Instead of falling on your side the wheels just lose momentum and slow down, but since you’re in practice always pedalling, you re-generate its momentum and stay balanced indefinitely as long as you can pedal.
There is a more accurate, more complex explanation (angular momenta, gyroscopes, etc.), but generally that’s what’s happening.
In high school physics you should have seen a demonstration of this, where your physics teacher has just the wheel in their hand, they make the wheel spin fast and hang the wheel on a thread that is tied to the axle of the bike wheel. If the bike wheel isn’t spinning it falls from vertical to horizontal in a very intuitive way, but when it’s spinning it just remains vertically upright (in a very unintuitive/surprising way), all because of the momentum described above.
The wheels spinning while moving create a strong gyroscopic effect.
If your bike wheels come off easily, remove one, hold it out in front of you between your arms by the axle so it can spin freely and then spin it really fast. You’ll notice it’s hard to twist or tilt in a different orientation now that it’s spinning.
This is because it’s angular momentum is essentially a pretty strong force in a specific direction around the axle and if you have a strong force moving in a direction then you’ll also need a strong force to change that direction.
While your moving this force helps balance the bike and if you move fast enough you can even take your hands of the handle bars because the angular moment will not only hold you upright but also in a straight line.
As soon as you stop moving the wheels are no longer generate any such force and you’re balancing all by yourself.
I like to play with this force whenever I change my tyres because it feels so weird to have the wheel resist me trying to tilt it.
[Here’s](https://youtu.be/ty9QSiVC2g0?t=55) a great 3 minute video which I’ve timestamped from the correct moment to see a wheel stabilise itself with a better explanation of you can’t do it with your own wheels.
The front wheel is very good at stabilizing the rest of the bike, but it only works if the bike is moving. A well-designed bike will right itself as it moves, since the forward wheel transforms any tilt into a curve, straightening out the bike. With a driver on top who can correct these curves and keep it in movement, it can remain standing for a very long time.
The tires and wheels act like gyroscopes when moving. When spinning, you tires/wheels have angular momentum and do not want to turn or tip over without significant force to make them do so.
Even most of the people who balance on a stopped bike are actually rolling it back and forth a tiny bit to stay upright.
I remember veritasium had a great video on this
[https://www.youtube.com/watch?v=9cNmUNHSBac](https://www.youtube.com/watch?v=ty9QSiVC2g0&t=55s)
Latest Answers