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Comment by jakedata | Hacker News Reader

While the monkey bars/climbing frame provided exercise and adventure in my elementary school playground, there was also this rotating hoop called a witch's hat which taught early lessons in conservation of momentum and unbalanced mass rotation.

I still remember the ringing sound of steel as someone on the opposite side lost their grip and was flung outwards, causing the person on the opposite side to crash into the pole.

See slide 15 for an illustration: https://honey.nine.com.au/parenting/retro-dangerous-playgrou...

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Example: https://everwas.com/2009/11/old-school-playground/

> there was also this rotating hoop called a witch's hat which taught early lessons in conservation of momentum and unbalanced mass rotation.

I loved that thing. Back in kindergarten we'd get the young student teachers to spin us as fast as they could and then the brazen of us would let go for our first experiences with flight. I'm incredibly grateful to have been part of the last class at Edwards Elementary that had access to that deathtrap, it was removed at the end of that year.

Hell, thinking about it now makes me want to weld up an adult version for my friends and I. Though, I think our increased mass might limit our fun; it'd probably "good" idea to power the rotation.

Every playground in the largely "health and safety"-free UK had those, until about the late 1980s when they all seemed to get cut away and scrapped almost simultaneously. While technically it's not actually illegal to crush small children with 300kg of scaff poles and keyclamps, it turns out that it *is* in fact frowned upon, and some sort of rule was introduced.

Well, there was also (at least here in Italy) what I call the great pavement revolution.

In the old times these structures were installed everywhere, if you were lucky it was grass or dirt, but gravel, concrete or asphalt were all common (roughly in ascending order of seriousness of bruises[1]).

Then, around the late '90's came out some new norms that imposed soft pavements and playgrounds were updated with these new floors (and new structures), UNI/BS EN 1176 and 1177.

[1] personally I have very few photos as a kid without one or both knees bruised, though riding the bycicle was another common cause

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