Killjoy comment obviated
Snopes says the bit about it being fur (not fir, as the Richard got the urban legend wrong...) is debunked...
This is merely a diversion, but a delightful one nonetheless: a mechanical engineer has answered a question posed on Quora, “What qualities would the glass in Cinderella's slippers need to have in order for her to walk and dance comfortably (and hold her weight)?” In the kind of what-if that probably has Randall Munroe over at …
Snopes says that glass is not a mistranslation from French to English because the French source for the English version of the story uses verre not vair. The word vair was no longer in use when the story was transcripted from oral accounts, so whoever told the story to Perrault probably said verre. Going back to the oldest know version of Cinderella (from China), the slippers were gold. Somehow during translation and being passed by word of mouth, gold became glass. I am sure the slippers were made from many different materials before verre. Perhaps vair was one of them.
“glass” is merely a confusion in translation, and the original slipper was probably fir.
I wood have thought it was fur not fir but then that just goes to show that the story survived all those centuries without a spell chequer.
Wikipedia has some interesting things to say about the story including:
"It is thought that the slipper was made of vair (a russian squirrel, petit-gris) rather than glass. Many tales are relayed by word of mouth then translated. It is likely that the word "vair" which sounds like "verre" in French, was taken to mean glass rather than fur. The text in French below explains the posible confusion between "verre" and "vair"."
So that's the squirrel fur the prince was interested in - not beaver!
Try reading the link in the first post.
In terms of engineering, this needs to be looked at in terms of low probability high impact event (LPHI) in that failure of the slipper would sends shards of glass deep into the wearers foot, particularly up the heel. Unlike today where idiots abound taking stupid risks because they believe modern medicine will save them from arbitrarily bad injuries, in the Middle Ages a chunk of glass 10cm up your heel would easily prove crippling for life, if not outright fatal. Hence the need to have very large margins in the glass slipper design.
"in that failure of the slipper would sends shards of glass deep into the wearers foot"
No, because (if you read the article) the design involves thermally hardend glass. The failure mode of this (aka toughened glass) is regularly demonstrated when cars crash, yobbos kick phone booth windows in and the like. All you get is a multitude of tiny fragments. Certainly enough to cause cuts when stood on, but specifically not long sharp edged shards that can cause serious injury.
Cooking, cleaning, and *abused*... Her figure would have been more along the lines of the modern cheesegrater-models, which incidentally was *not* the ideal of beauty at the time, since your average maid looked like that. The real pretty girls were "rubentian" in build, signifying affluence and health. Given that people were shorter on average as well, 50kg may well be on the heavy side.
Mind.. the slippers could easily have been "glass", if heavily decorated with beads, especially venetian glass, which was at least good enough for several dresses of Elisabeth I, who by all accounts was *very* keen on the principle "dress to Impress".
Thus when standing still there would be ~250N on the slipper.
When walking this would increase to well above 500N, as there are impact forces to consider, as well as a failure mode that didn't amputate the wearer's foot, so toughened glass would clearly be a minimum requirement.
Perhaps he made the hidden starting assumption that she'd already had a terrible accident with a previous design of glass slipper?
OK, first the slippers were"magic" because it was a fairy godmother that whipped them up, so even though the original story probably had the slippers as something other than glass. lets say for the argument, that they were a transparent glass like substance like Aluminium oxynitride or AlON. this is often called Transparent aluminum. (not kidding, look it up yourself and ignore the Star Trek references) this substance seems to be quite capable of doing the job. is't very expensive, but hey the Fairy Godmother had invested wisely...
once you let the thought outside of the box , it can go anywhere!
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