Nodding to the ancient but elegant hour glass that drops fine sand through the canonical “hourglass” shape, awaglass streams bubbles up through the hourglass. It’s kind of a cool effect, and certainly fascinating in an analog way.
You can’t actually keep time with this device, the physics of bubbles is much more complicated than (tiny) falling rocks. It is easy to see that the bubbles are not all the same size. It is visible but less obvious that there is a complex exchange of heavier fluid falling that forces lighter bubbles to rise, and they have to pass each other in the narrow neck of the hourglass. This fluid dynamic system is certainly complicated and likely chaotic. Not so good for timekeeping.
This piece made me think a little. Why does the sand-based hourglass work and the bubble-based one fail? Both are powered by gravity. Both are exchanging two materials of different densities, via a constrained opening that restricts the flow. One of the materials is invisible and the other is visually compelling, though both are actually keeping time. But one is solid+gas and the other is liquid+gas, and thereby hangs a tale.
Geometry is important. The size of the sand particles matters (and they must be pretty uniform). The size of the bubbles matters, and it isn’t easy to control that. For that matter, they tend to change size in funny ways as they split and merge.
Friction is important. The sand is relatively slippery, the grains do not clump. The bubbles are definitely clumpy.
Both are powered by gravity, which makes me realize that the sand hourglass will not work on the space station, and will run slow (or even stop) on the moon. I had never thought about this, but it makes that little kitchen timer a real “Earthy” thing. Cool!
Finally, awaglass makes me wonder what it would take to actually keep time with bubbles. Can we great bubbles that are uniform and slippery enough to keep time? Perhaps the notorious microbeads would work?
On another tack, could we build one that used icecubes floating in (supercooled?) water? Tiny, Icegrains? Snowflakes! (Obviously, this icy hourglass only works if it is kept cold.)
Obviously, this isn’t practical technology, but it sure made me think. I love it.