This bizarre density toy just got an upgrade

I have the 'original' polydensity kit from Ed Inn (now Flinn, blech), and it's a fascinating toy.

Two insoluble liquids and two types of beads - pony and UV - which make for some fascinating behavior when the bottle is shaken and allowed to settle and separate.

In today's video, Steve Mould attempts to make a similar bottle with three insoluble liquids and four polymer beads.

He does achieve his desired result by the end, but the beads he uses look to be a little tougher to source.

Sadly so...

Pop-Pop Boats Are Weirder Than You Think

I've never heard of a Pop-Pop Boat before, so it's really not any weirder than I thought it was because I'd never thought of it at all.

Turns out the science of a pop-pop boat isn't all that different from the drinking bird. There's a contained amount of gas that is warmer than another amount of gas. That warmness causes the gas to expand and pushes liquid blocking that gas. In the case of the drinking bird, that unbalances the bird and makes it tip over. In the case of the pop-pop boat that liquid pushes the boat forward in a halting way.

Steve Mould's see-through model of the pop-pop boat doesn't, sadly, make the same pop-pop sound because there's no metal to snap back and forth, but it is a great way to see the inner workings of the boat.

The Engineering of the Drinking Bird

I would make a Darkman reference, but I'm guessing nobody would get it.

Maybe a Simpsons reference would be better.

This video goes through the liquid evaporating on the head of the bird...causing cooling in the head...causing a decrease in pressure in the head...causing the lower bulb's greater pressure to push the liquid into the head...causing the center of gravity of the bird to shift slightly forward...causing the liquid in the base to drop below the level of the inner tube...causing the vapor from the bottom bulb to flow through the tube and equalize pressure between the two bulbs and liquid to shift back down...the process repeats as long as the bird'd beak can 'drink' to stay wet and - as Bill points out - the humidity is low enough to allow evaporation.

This is also how hand boilers work.

I'd never heard the temperature difference's connection to heat engines (referenced previously on the blog). That's a nice connection there, Bill.

Color magic barbie

It's weird how frequently interesting chemistry can be found when you're open to finding it in the wild. Take, for example, this post from Katydid, a former student of mine. The color-changing nature immediately made me think of acid-base indicators, and the note toward the end of the ad copy, "make new solutions with vinegar or baking soda" pretty well locked down my assumptions.

I'm not sure what non-toxic, color-safe indicators are being used (pink to yellow, blue to pink, other color combos), but I'm feeling safe with my indicator assumption.