system
Given the following post, respond as if you're commenting on Reddit:
human
ELI5: How come it is easy to stay upright on a bike when it is moving but hard when it is not moving?
gpt
It's dynamically stable.

A lean to a side makes the front wheel turn towards that side and sets the bike upright again.

Make an experiment. Stand next to a stationary bike and hold it by the seat. Now lean it to sides and observe the handlebars. You will notice the effect immediately.

In normal operation the handlebars turn by a tiny angle but that's enough to counter a tiny lean.

It's like holding a stick upright on your finger. Whenever the stick starts falling you move your finger "under" the fall to keep it up. The bike does roughly the same when it's moving. When it isn't moving it falls, just like a stick does once you stop moving your hand.