Marguerite Vela

Short version: a moving bike stays up because the front wheel steers itself back under the falling mass, and because the rider steers too. Balance is a steering problem, not a spinning problem.

When the bike leans left, two things push the front wheel to steer left. One is trail, the horizontal gap between where the steering axis would meet the ground and where the tyre actually touches, which makes the contact patch behave like a caster on a shopping trolley. The other is that the mass of the fork and wheel sits off the steering axis, so gravity itself turns the bars into the lean. Steering into the lean drags the tyres back under the centre of mass and the bike stands up again.

At zero speed none of that helps, because turning the wheel no longer moves the contact patch anywhere useful. That is the entire difference.

Demo: walk a bike alongside you with no rider, give it a push and a small sideways nudge. It corrects itself and keeps rolling. Then hold the bars rigidly straight and push it again. It falls over almost immediately.

The angular momentum of a bicycle wheel is small compared with the torque of a leaning rider, though. You can check that roughly with a wheel mass and normal speeds. It contributes a little, it is not what is holding you up.

On the moss specifically, set your expectations lower. Moss on a background either establishes in the first couple of months or slowly browns off, and it is very sensitive to how consistently that surface stays damp. If it has not visibly greened up and spread by month three, it probably will not, and a moss slurry applied to an already damp background works better than sheets pinned on dry.

You can watch this with a bottle of water taken slowly below freezing in the freezer door. Tap it and the whole thing goes white in about two seconds. Best nucleation demo available with kitchen equipment.

The heat lamp is doing a lot of the work here too. If your animal does not strictly need a basking bulb, switching to a lower wattage or to a different heat source will flatten the curve considerably. A big daytime swing from a bright hot bulb over a screen is fighting exactly what you are trying to achieve.

There is a normal population cycle too. Springtails boom on the initial flush of decaying material in a new tank, then settle to a much lower steady population once the easy food is gone. Two months is about right for that transition, so some of what you are seeing may just be the tank finding its level rather than anything going wrong.

One extra reason your eyes win: dynamic range and adaptation. Your eye is looking at a small bright thing and adjusting locally, while the camera makes one global decision for the whole frame. That is also why a photo of the moon over a landscape never looks like what you saw. If you want both, you take two exposures and combine them, and every dramatic moon over a building photo you have ever seen was made that way or with a very long lens compressing the scene.

Wind is the other variable people forget. A breeze breaks up the plume before the droplets grow enough to scatter light, so identical conditions look dramatic in a sheltered doorway and invisible in the open. Try exhaling with your back to the wind next time and see if it comes back.

One more consideration for a tall build: get your background and any mounting done before the drainage layer goes in. Working in a 36 inch tall tank with three inches of wet substrate already at the bottom is miserable, and anything you drop lands somewhere you cannot easily reach.