1. Oh, you don’t remember these things? They were great. They were little rubber domes maybe the diameter of a quarter or so, and you turned them inside out and put them on the ground, and they would sit there for a little bit, then snap back to their dome-shape and fling themselves into the air.

  2. Jon says: “XKCD has a page explaining it. ”

    Thanks for the reminder about Explain XKCD. It’s a useful resource when XKCD has you stumped.

    I don’t know much about their relationship, but from the history at https://www.explainxkcd.com/wiki/index.php/explain_xkcd I get the idea the Explain site is mostly independent, so that it’s a little off to say “XKCD has a page explaining it. “

  3. I didn’t experience these personally, but I gather 90’s kids would set these up in various places and leave them to pop up randomly and catch their parents unaware. I have no idea how they all mysteriously vanished.

  4. The metal ones are bimetallic, so it’s two layers of metals with dissimilar expansion rates, in a convex shape, with a flat outer rim.

    You ‘set’ them by heating them up by rubbing them between your fingers, then flex them so the center is concave, and place them down on a hard surface. As they cool, at some point, the different expansion of the metals will cause it to spring back to it’s original convex shape, flipping a few feet into the air in the process.

    Edmunds Scientific used to sell some that had a sticker that made it look like a quarter.

    The ones that look plastic are a kind of rubber that also eventually returns to it’s original convex shape.

  5. I deliberately didn’t look at ExplainXKCD, since then we would never have the pleasure of having XKCD here. 😉

  6. There’s no air seal involved, in any case. It’s more a matter of the shape having a nonlinear response to inverting.

  7. Thanks for all the explanations of the mechanism!
    I was thinking about “air seal” because I’ve been dealing with a “shower caddy” that is supposed to affix to tile by suction cups; but always fails after a while.

  8. There’s no air seal, provided that the popper is used the way it’s supposed to be used.

    However, back in the 1980s, I (and I’m sure a lot of other children) discovered that you could push the poppers onto your bare skin and have them stay there. The suction due to the air seal formed between the rubber popper and your skin was enough to keep the popper in place for at least a few minutes.

    After which, when they fell off, you’d have a visible hickey for the next couple of days.

  9. Did those have a surge int the 90s because they’ve been around a lot longer than that. I played with them in 75. And does anyone think those are a thing to quintessentially define 90s childhood? (They certainly did not define 70’s childhood.)

  10. I’m with Daniel J. Drazen on this one; it’s a new spin (see what I did there?) on the old propeller beanies. I used to have one, or rather a propeller baseball cap. The support for the prop was a little plastic Marvin the Martian, and it had a K-9 patch on the front. None of which is relevant to the joke but I knew you would all be fascinated by the info.

  11. Oh, and yes, I was an adult when I got it, and I wore it in public. I have no pride, I have no shame.

  12. In the late 1950s (when I was born) there was a cartoon on TV called “Beany & Cecil”. Beany was a kid who wore a propeller beanie, and Cecil was “the Seasick Sea Serpent”. In 1961 when I was four years old, I came down with chicken pox. My dad got me a “Beany Copter” to keep me entertained and get my mind off the itching. This was a plastic hat with a windup propeller. After winding, you pulled a string and the prop flew off to the ceiling. I wore that thing out!

  13. In completely unrelated stuff except that it involves weird hats called “beanies” and tangentially geek stuff — comics, in this case — do you know what Jughead’s “crown” is supposed to be? I mean, now it’s a crown, because the original hat type is lost to time — but at the time that the Archie comics were created, there was this thing were you would take an old fedora, turn it inside out, and cut the brim into triangles. Then you could, optionally, stick the triangles up with collectable pins and/or buttons. This was associated with teenagers, especially, but not exclusively, juvenile delinquents. Another culturally significant beanie-by-that-definition wearer was Encyclopedia Brown’s nemesis Bugs Meany.

    After reading that thing, I attempted to make a jughead hat out of an old fedora I had after it wore out. It… didn’t work. I THINK I know what I did wrong, and I might try it again in ten or twenty years when my current fedora wears out.


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